All living things are composed of cells.  This concept leads to the development of the contemporary cell theory, which incorporates several basic concepts: 

     1. Cells are the structural “building blocks” of all plants and animals 

    2. Cells are developed by the division of preexisting cells 

   3. Cells are the smallest units that perform all vital functions.

The body contains two cell types: sex cells (germ cells or reproductive cells) and somatic cells (or body cells). Sex cells are either the sperm of males or the oocytes of females. Somatic cells are all the other cells in the body.

Cytology is the study of the structure and function of individual cells. The two most common methods used to study cell tissue structure are light microscopy and electron microscopy. Light microscopy uses light to permit magnification and viewing of cellular structures up to 1000 times their natural size. Electron microscopy uses a focused beam of electrons to magnify cell structure up to 1000 times what is possible by light microscopy.

Cellular Anatomy

A cell is surrounded by a thin layer of extracellular fluid. The cell's outer boundary is the cell membrane (or plasma membrane).It is extremely thin and delicate, and has a complex structure composed of phospholipids, proteins, glycolipids, and cholesterol. The cell membrane is called a phospholipid bilayer because its phospholipids form two distinct layers. 

There are two general types of membrane proteins. Peripheral proteins are attached to either the inner or the outer membrane surface. Integral proteins are embedded in the phospholipid bilayer of the membrane. Some of the integral proteins form channels that allow water molecules, ions, and small water-soluble compounds into or out of the cell. Some channels are called gated channels because they can open or close to regulate the passage of materials. 

The general functions of the cell membrane are:

1.      Physical isolation: The lipid bilayer of the cell membrane forms a physical barrier that separates the inside of the cell from the surrounding extracellular fluid

2.      Regulation of exchange with the environment: The cell membrane controls the entry of ions and nutrients, the elimination of wastes, and the release of secretory products.

3.      Sensitivity: The cell membrane is the first part of the cell affected by changes in the extracellular fluid. It also contains a variety of receptors that allow the cell to recognize and respond to specific molecules in its environment, and to communicate with other cells.

     4.      Structural support: Specialized connections between cell membranes or between membranes and extracellular materials give tissues a stable structure. 

The permeability of a membrane is a property that determines it effectiveness as a barrier. The greater the permeability, the easier it is for substances to cross the membrane. If nothing can cross a membrane, it is described as impermeable. If any substance can cross without difficulty, the membrane is freely permeable. Cell membranes are selectively permeable, that is they permit the free passage of some materials.
Diffusion is the net movement of material from an area where its concentration is high to an area where its concentration is lower. The difference between the high and low concentrations represents a concentration gradient.  Diffusion occurs until the concentration gradient is eliminated. When the concentration gradient has been eliminated, equilibrium exists. 
Diffusion of water across a membrane from a region of high water concentration to a region of low water concentration is called osmosis.

Facilitated diffusion is a passive transport process that requires the presence of carrier proteins. The molecule to be transported first binds to a receptor site on an integral membrane protein. It is then moved to the inside of the cell membrane and released into the cytoplasm.

All active membrane processes require energy in the form of adenosine triphosphate (or ATP). Two important active processes are active transport and endocytosis.

Active transport mechanisms consume ATP and are not dependent on concentration gradients. All living cells show active transport of sodium, potassium, calcium, and magnesium. Specialized cells can transport additional ions such as iodide or iron. Many of these carrier mechanisms, known as ion pumps, move a specific cation or anion in one direction, either into or out of the cell. If one ion moves in one direction while another moves in the opposite direction, the carrier is called an exchange pump. 

Endocytosis is movement into a cell and is an active process that occurs in one of three forms: pinocytosis (cell drinking), phagocytosis (cell eating), or receptor-mediated endocytosis (selective movement).
The formation of pinosomes, or vesicles filled with extracellular fluid, is the result of a process called pinocytosis. In this process, a deep groove or pocket forms in the cell membrane and then pinches off. Nutrients such as lipids, sugars, and amino acids, then enter the cytoplasm by diffusion or active transport from the enclosed fluid. The membrane of the pinosome then returns to the cell surface.

Solid objects are taken into cells and enclosed within vesicles by phagocytosis. Cytoplasmic extensions called pseudopodia surround the object, and their membranes fuse to form a vesicle known as a phagosome. The phagosome may then fuse with a lysosome, where its contents are digested by lysosomal enzymes. 

Receptor-mediated endocytosis is a process that resembles pinocytosis, but is far more sensitive. Pinocytosis produces pinosomes filled with extracellular fluid; receptor-mediated endocytosis produces coated vesicles that contain a specific target molecule in high concentrations. The target substances, called ligands, are bound to receptors on the membrane surface. 

The Cytoplasm

 
The cytoplasm contains cytosol, an intracellular fluid that surrounds structures that perform specific functions, called organelles.

Cytosol is significantly different from extracellular fluid. Three important differences are:

1.      The cytosol contains a high concentration of potassium ions, whereas extracellular fluid contains a high concentration of sodium ions. 

2.      The cytosol contains a relatively high concentration of dissolved and suspended proteins. 

3.      The cytosol contains relatively small quantities of carbohydrates and large reserves of amino acids and lipids. 

The cytosol of cells contains masses of insoluble materials known as inclusions, or inclusion bodies. 

Organelles are found in all body cells. Cellular organelles can be divided into two categories: nonmembranous organelles and membranous organelles. No membranous organelles are not enclosed in membranes, and are always in contact with the cytosol. These include the cytoskeleton, microvilli, centrioles, cilia, flagella, and ribosomes. Membranous organelles are surrounded by membranes that isolate their contents from the cytosol, just as the cell membrane isolates the cytosol from the extracellular fluid.

Nonmembranous Organelles

The cytoskeleton is an internal protein network that gives the cytoplasm strength and flexibility. It has four components: microfilaments, intermediate filaments, thick filaments, and microtubules.

 

Microfiliments have two major functions:

1.      They anchor the cytoskeleton to integral proteins of the cell membrane

2.      Actin microfilaments can interact with microfilaments or larger structures composed of the protein myosin.

Intermediate filaments:

1.      Provide strength

2.      Stabilize the position of organelles

3.      Transport materials within the cytoplasm

Specialized intermediate filaments, called neurofilaments, are found in neurons, where they provide structural support within axons, long cellular processes that may be up to a meter in length.

 Thick filaments are relatively massive filaments composed of myosin protein subunits. They are abundant in muscle cells, where they interact with actin filaments to produce powerful contractions.

All cells possess hollow tubes called microtubules, which are built from the global protein tubulin. Microtubules have a variety of functions:

1.      Microtubules from the primary components of the cytoskeleton, giving the cell strength and rigidity and anchoring the positions of major organelles.

2.      The assembly and/or disassembly of microtubules provides a mechanism for changing the shape of the cell, perhaps assisting in cell movement.

3.      Microtubules can attach to organelles and other intracellular materials and move them around within the cell.

4.      During cell division, microtubules form the spindle apparatus that distributes the duplicated chromosomes to opposite ends of the dividing cell. 

5.      Microtubules form structural components of organelles such as centrioles, cilia, and flagella. 

Microvilli are small, fingerlike projections of the cell membrane that increase the surface area exposed to the extracellular environment. A network of microfilaments stiffens each  microvillus and anchors it to the terminal web, a dense supporting network within the underlying cytoskeleton. Interactions between these microfilaments and the cytoskeleton can produce a waving or bending action. Their movements help circulate fluid around the microvilli, bringing dissolved nutrients into contact with receptors on the membrane surface.

Centriloes are small, microtubule-containing cylinders that direct the movement of chromosomes during cell division. Cells that do not divide, such as mature red blood cells and skeletal muscle cells, lack centrioles. The centrosome is the region of the cytoplasm surrounding this pair of centrioles. It directs the organization of the microtubules of the cytoskeleton.

Cilia, anchored by a basal body, are microtubules containing hairlike projections from the cell surface that beat rhythmically to move fluids or secretions across the cell surface.

A whiplike flagellum moves a cell through surrounding fluid, rather than moving the fluid past a stationary cell. The sperm cell is the only human cell that has a flagellum.

Ribosomes are intracellular factories consisting of small and large subunits, together they manufacture proteins. Two types of ribosomes, free (within the cytosol) and fixed (bound to the endoplasmic reticulum) are found in cells.

Membranous organelles are surrounded by lipid membranes that isolate them from the cytosol. They include: mitochondria, the nucleus, the endoplasmic reticulum (rough and smooth), the Golgi apparatus, lysosomes, and peroxisomes.

Mitochondria are responsible for producing 95% of the ATP within a typical cell. They are organelles that have an unusual double membrane. An outer membrane surrounds the entire organelle, and a second, inner membrane contains numerous folds called cristae. Cristae increase the surface area exposed to the fluid contents (or matrix) of the mitochondrion. The matrix contains metabolic enzymes that perform the reactions that provide energy for cellular functions.

The nucleus is the control center for cellular operations. It is surrounded by a nuclear envelope, through which it communicates with the cytosol through nuclear pores.  The nuclear envelope is a double membrane enclosing a narrow perinuclear space. The term nucleoplasm refers to the fluid contents of the nucleus.

 The nucleus contains 23 pairs of chromosomes. Each chromosome contains DNA strands bound to special proteins called histones. At intervals the DNA strands wind around the histones, forming the complex known as a nucleosome. The chromosomes have direct control over the synthesis of RNA. Most nuclei contain one to four dark-staining areas called nucleoli. Nucleoli are nuclear organelles that synthesize the components of ribosomes. 

 The endoplasmic reticulum (ER) is a network of intracellular membranes involved in synthesis, storage, transport, and detoxification. The ER forms hollow tubes, flattened sheets, and rounded chambers called cisternae. There are two types of ER, rough and smooth. Rough endoplasmic reticulum (RER) has attached ribosomes; smooth endoplasmic reticulum (SER) does not. 

The ER has four major functions:

1.      Synthesis: The membrane of the ER contains enzymes that manufacture carbohydrates and lipids; areas with fixed ribosomes synthesize proteins. These manufactured proteins are stored in the cisternae of the ER.

2.      Storage: The ER can hold synthesized molecules or substances absorbed from the cytosol without affecting the other cellular operations.

3.      Transport: Substances can travel from place to place within the cell inside the ER.

4.      Detoxification: Cellular toxins can be absorbed by the ER and neutralized by enzymes found on its membrane.

 

The Golgi apparatus consists of flattened membrane discs called cisternae. The major functions of the Golgi apparatus are:

1.      Synthesis and packaging of secretions, such as mucins or enzymes

2.      Packaging of special enzymes for use in the cytosol

3.      Renewal or modification of the cell membrane.

Material moves between cisternae by means of small transfer vesicles. Vesicles contain secretions that will be discharged from the cell are called secretory vesicles. Secretory products are discharged from the cell through the process of exocytosis.

Lysosomes are vesicles filled with digestive enzymes. Primary lysosomes contain inactive enzymes. Activation occurs when the lysosome fuses with the membranes of damaged organelles, such as mitochondria or fragments of the ER. This fusion creates a secondary lysosome, which contains active enzymes. These enzymes then break down the lysosomal contents. The process of endocytosis is important in ridding the cell of bacteria and debris. The endocytic vesicle fuses with a lysosome, resulting in the digestion of its contents.

Peroxisomes carry enzymes used to break down organic molecules and neutralize toxins. (That’s all I have to say about that). 

 Membrane Flow

There is a continuous movement of membrane among the nuclear envelope, Golgi apparatus, endoplasmic reticulum, vesicles, and the cell membrane. This is called membrane flow. It provides a mechanism for cells to change the characteristics of their cell membranes as they grow, mature, or respond to a specific environmental stimulus.

 

Intercellular Attachment

Cells attach to other cells or to extracellular protein fibers by three different types of cell junctions: tight junctions, gap junctions, and desmosomes. Cells in some areas of the body are linked by combinations of cell junctions.

At a tight junction, bands of interlocking membrane proteins bind together the adjoining cell membranes; these are the strongest intercellular connections.

In a gap junction, two cells are held together by interlocking membrane proteins called connexons. These are channel proteins, which form a narrow passageway.

A desosome has a very thin proteoglycan layer between the cell membranes, reinforced by a network of cytokeratin filaments. Button desmosomes are small discs connected to bands of intermediate fibers. A hemidesmosome attaches a cell to extracellular filaments and fibers. (Check out page 43 Figure 2.19 for a good picture of cell attachments).

The Cell Life Cycle

Cell division is the reproduction of cells. Reproductive cells produce gametes (sperm or oocytes) through the process of meiosis. In a dividing cell, an interphase or growth period alternates with a nuclear division phase, termed mitosis.

Most somatic cells spend most of their time in interphase, a time of growth. Interphase can be divided into G1, S and G2 phases. (Check out page 44 Figure 2.20 for a good picture of The Cell Life Cycle.)

 Mitosis refers to the nuclear division of somatic cells.

 Mitosis proceeds in four distinct, continuous stages: prophase, metaphase, anaphase and telophase.

 Prophase begins when the chromosomes coil so tightly they become visible as individual structures. Metaphase is when spindle fibers pass among the chromosomes, and the kinetochore of each chromatid becomes attached to a spindle fiber called a chromosomal microtubule. Anaphase is when the chromatid pairs separate, and the daughter chromosomes move toward opposite ends of the cells. Anaphase ends as the daughter chromosomes arrive near the centrioles at opposite ends of the dividing cells. Telophase is where the nuclear membranes form and the nuclei enlarge as the chromosomes gradually uncoil. Once the chromosomes disappear, nucleoli reappear and the nuclei resemble those of interphase cells. 

 During cytokinesis, the last step in cell division the cytoplasm is divided between the two daughter cells. 

 In general, the longer the life expectancy of a cell type, the slower the mitotic rate. Stem cells undergo frequent mitosis to replace other, more specialized cells. 

I found this to be a really fun chapter (and also wicked quick, it’s only like 15 pages), so this blog is going to be a little short. Anyway, on to Human Development!

Development is the gradual modification of physical and physiological characteristics from conception to maturity. The creation of different cell types during development is called differentiation. Differentiation occurs through selective changes in genetic activity. A basic appreciation of human development provides a framework for enhancing the understanding of anatomical structures. (Although I guess they’re assuming we have a basic appreciation for Anatomy in the first place…)

An Overview of Development

 Development involves:

1. the division and differentiation of cells
2. reorganization of those cell types to produce or modify anatomical structures

 
Development is a continuum that begins at fertilization (or conception) and can be separated into periods characterized by specific anatomical changes. Prenatal development occurs in the period from conception to delivery. Embryology refers to the study of the developmental events that occur during prenatal development. Postnatal development commences at birth and continues to maturity (although some of us reach a more mature level than others…)

 
Prenatal development can actually be subdivided further. Pre-embryonic development begins at fertilization and continues through cleavage (an initial series of cell divisions) and implantation (the movement of the pre-embryo into the uterine lining).

Pre-embryonic development is followed by embryonic development, which extends from implantation, typically occurring on the ninth or tenth day after fertilization, to the end of the eight developmental week. Fetal development begins at the start of the ninth developmental week and continues up to the time of birth.

Fertilization

Fertilization normally occurs in the ampulla of the uterine tube within a day after ovulation. Sperm cannot fertilize an egg until they have undergone capacitation. Around 200 million sperm are ejaculated into the vagina, and only around 100 will reach the ampulla. A man with fewer than 20 million sperm per milliliter is functionally sterile.

The Oocyte at Ovulation (look at Figure 28.1b)

Ovulation occurs before the completion of oocyte maturation, and the secondary oocyte leaving the follicle is in metaphase of the second meiotic division (or meiosis II). Metabolic operations have also been discontinued, and the secondary oocyte drifts in a sort of suspended animation, awaiting the stimulus for further development. If fertilization does not occur, it will disintegrate without completing meiosis. The acrosomal caps of the spermatozoa release hyluronidase, an enzyme that separates cells of the corona radiate and exposes the oocyte membrane. When a single spermatozoon contacts that membrane, fertilization occurs and oocyte activation follows.

During activation the secondary oocyte completes meiosis. The female pronucleus then fuses with the male pronucleus, a process called amphimixis.

Prenatal Development

The nine-month gestation period can be divided into three trimesters, each three months in duration.

The first trimester is the period of embryonic and early fetal development. During this period the rudiments of all the major organs systems appear

In the second trimester the organs and organ systems complete most of their development. The body proportions change, and by the end of the second trimester the fetus looks distinctively human.

The third trimester is characterized by rapid fetal growth. Early in the third trimester most of the major organ systems become fully functional.
 

Let’s look at these trimesters a little more closely…

The first trimester is the most critical period in prenatal life. There are four general processes that occur during this trimester.

1. Cleavage subdivides the cytoplasm of the zygote in a series of mitotic divisions; the zygote becomes a blastocyst.
2. During implantation the blastocyst burrows into the uterine endometrium and continues as the blastocyst invades the uterine wall.
3. Placentation occurs as blood vessels form around the blastocyst and the placenta appears. The placenta provides the link between maternal and embryonic systems; it provides respiratory and nutritional support essential for further prenatal development.
4. Embryogenesis is the formation of a viable embryo. This process forms the body of the embryo and its internal organs.

Cleavage is a series of cell divisions that subdivides the cytoplasm of the zygote into smaller cells called blastomeres. The blastomeres then form a hollow ball, the blastocyst with an inner cavity known as the blastocoele. The blastocyst consists of an outer trophoblast and an inner cell mass.

Implantation begins as the surface of the blastocyst closest to the inner cell mass touches and adheres to the uterine lining. The trophoblast next to the endometrium undergoes changes and becomes a synctial trophoblast, which then erodes a path through the uterine epithelium. As the trophoblast enlarges and spreads, maternal blood flows through trophoblastic channels, or lacunae. The blastocyst organizes into layers and becomes a blastodisc.

After gastrulation the blastodisc contains an embryo composed of endoderm, ectoderm, and an intervening mesoderm. These germ layers help form four extraembryonic membranes; the yolk sac (endoderm and mesoderm), amnion (which is ectoderm and mesoderm), allantois (endoderm and mesoderm), and chorion (mesoderm and trophoblast). These membranes support embryonic and fetal development by maintaining a consistent, stable environment and by providing access to the oxygen and nutrients carried by the maternal bloodstream.

The yolk sac, the first of the extraembryonic membranes, is an important site of blood cell formation. The amnion encloses amniotic fluid that surrounds and cushions the developing embryo. The base of the allantiois layer gives rise to the urinary bladder. Circulation within the vessels of the chorion provides a rapid-transit system linking the embryo with the trophoblast.

Placentation

The appearance of blood vessels in the chorion is the first step in the formation of a functional placenta. Chorionic villi extend outward into the maternal tissues, forming an intricate, branching network through which maternal blood flows. The body stalk and the yolk stalk connect the embryo with the chorion and the yolk sac, respectively. As development proceeds, the umbilical cord connects the fetus to the placenta. Blood flow occurs through the umbilical arteries and the umbilical vein, and exchange occurs at the chorionic villi. The placenta synthesizes HCG, estrogens, progestins, HPL, and relaxin.

Embryogenesis

The embryo, which has a head fold and a tail fold, will undergo critical changes in the first trimester. Events in the first 12 weeks establish the basis for organogenesis (organ formation).

In the second trimester, the organ systems near functional completion and the fetus grows rapidly. During the third trimester, the organ systems become functional and the fetus undergoes its largest weight gain. By the end of gestation, the uterus will be about 12 inches long and contain almost 5 liters of fluid.

 
Labor and Delivery

The goal of true labor is parturition, the forcible expulsion of the fetus. God, that sounds horrible.

Labor can be divided into three stages: dilation stage, expulsion stage, and placental stage. The dilation stage, in which the cervix dilates, usually lasts eight or more hours (ouch). The expulsion stage involved the birth (delivery) of the fetus. Ok, so speaking of ouch: If the vaginal canal is too small to permit the passage of the fetus, and there is acute danger of perineal tearing, the passageway may be temporarily enlarged by making an incision through the perineal musculature (called an episiotomy). And we all know how they “temporarily enlarge” the passageway.

During the placental stage of labor, the muscle tension builds in the walls of the partially empty uterus, and the organ gradually decreases in size. The uterine contraction tears the connections between the endometrium and the placenta. Usually within one hour after delivery, the placental stage ends with the ejection of the placenta, or afterbirth. (yuck)

Premature Labor

Premature labor occurs before the fetus has completely developed. An infant born weighing less than 400g will not survive, however if the newborn weighs over 1kg, its chances range from fair to excellent, depending on the individual circumstances.

The neonatal period extends from birth to one month of age. Here’s a quick summary of the transition from fetus to neonate:

1. The lungs at birth are collapsed and filled with fluid, and filling them with air involves a massive and powerful inhalation
2. When the lungs expand, the pattern of cardiovascular circulation changes because of alterations in blood pressure and flow rates.
3. Typical heart rates of 120-140 beats/minute and respiratory rates of 30 breaths/minute in neonates are normal, and considerably higher than those of adults.
4. Prior to birth, the digestive system remains relatively inactive, although it does accumulate a mixture of bile secretions, mucus, and epithelial cells. This collection of debris is excreted in the first few days of life.
5. As waste products build up in the arterial blood, they are filtered into the urine at the kidneys. Glomerular filtration is normal, but the urine cannot be concentrated to any significant degree. As a result, urinary water losses are high, and neonatal fluid requirements are much greater than those in adults.
6. The neonate has little ability to control body temperature, particularly in the first few days of delivery. As the infant grows larger and increase the thickness of its insulating subcutaneous adipose “blanket”, its metabolic rate also rises.

So, ya, that’s it. Good luck on the exam everyone! And don't forget the practical!

The human reproductive system produces, stores, nourishes, and transports functional gametes (reproductive cells). Fertilization is the fusion of a sperm from the male and an immature ovum from the female. Fertilization produces a zygote, which is a single cell whose growth, development, and repeated divisions, will, in about nine months, produce a baby.

Organization of the Reproductive System

 The reproductive system includes:

1. Reproductive organs (or gonads) which produce gametes and hormones
2. A reproductive tract, consisting of ducts that receive, store, and transport the gametes
3. Accessory glands and organs that secret fluids into the ducts of the reproductive system or into other excretory ducts
4. Perineal structures associated with the reproductive system, collectively known as the external genitalia.

 
In the male, the testes produce sperm, which are expelled from the body in semen during ejaculation. The ovaries of a sexually mature female produce an egg that travels along uterine tubes to reach the uterus. The vagina connects the uterus with the exterior.

 
This is how babies are made, according to our book:
During intercourse, male ejaculation introduces semen into the vagina, and the sperm cells may ascend the female reproductive tract, where they may encounter an oocyte and begin the process of fertilization.

So, if/when you have kids, and they finally ask you how babies are made, just tell them that!

 
Anatomy of the Male Reproductive System

 
The spermatozoa (which are sperm cells) travel along the epididymis, the ductus deferens (or vas deferens), the ejaculatory duct, and the urethra before leaving the body. Accessory organs (notably the seminal vesicles, prostate gland, and bulbourethreal glands) secrete into the ejaculatory ducts and urethra. The external genitalia include the scrotum (which encloses the testes) and the penis (which is an erectile organ through which the distal portion of the urethra passes).

The Testes

 
The testes hang within the scrotum, and each measures about 2 in long and 1 inch in diameter.

The descent of the testes through the inguinal canals occurs during development. Before this time, the testes are held in place by the gubernaculum testis, which is a cord of connective tissue and muscle fibers that extends from the inferior part of each testis to the posterior wall of a small, inferior pocket of the peritoneum. During the seventh developmental month, differential growth and contraction of the gubernaculums testis causes the testes to descend.

 
Layers of fascia, connective tissue, and muscle collectively form a sheath, the spermatic cord, which encloses the ductus deferens, the testicular artery and vein, the pampiniform plexus, and the ilioinguinal and genitofemoral nerves.

The testes remain connected to the abdominal cavity through the spermatic cords. Each spermatic cord contains the ductus deferens, the testicular artery, the pampiniform plexus of the testicular vein, and the ilioinguinal and genitofermoral nerves from the lumbar plexus.

 
The Scrotum and the Position of the Testes

The scrotum is divided internally into two separate chambers. The perineal raphe marks the boundary between the two chambers in the scrotum. Each testis lies in its own scrotal cavity.

Concentration of the dartos muscle gives the scrotum a wrinkled appearance; the cremaster muscle pulls the testes closer to the body. The tunica vaginalis is a serous membrane that covers the tunica albuginea, the fibrous capsule that surrounds each testis.

 
Structure of the Testes

Septa extend from the tunica albuginea to the mediastinum, creating a series of lobules. Seminiferous tubules within each lobule are the sites of sperm production. From there, sperm pass through a straight tubule to the rete testis. Efferent ducts connect the rete testis to the epididymis. Between the seminiferous tubules, interstitial cells secrete male sex hormones called androgens (remember those?)

 
Testosterone is the most important androgen. It functions to:

1. Stimulate spermatogenesis
2. Promote the physical and functional maturation of spermatozoa
3. Maintain the accessory organs of the male reproductive tract
4. Cause development of secondary sexual characteristics by influencing the development and maturation of nonreproductive structures such as the distribution of facial hair and adipose tissue, muscle mass, and total body size
5. Stimulate growth and metabolism throughout the body
6. Influence brain development by stimulating sexual behaviors and sexual drive.

Spermatogenesis and Meiosis

Seminiferous tubules contain spermatogonia, stem cells involved in spermatogenesis (the production of sperm). The spermatogonia produce primary spermatocytes, diploid cells ready to undergo meiosis.

 
Meiosis is a special form of cell division that produces gametes. Mitosis and meiosis differ significantly in terms of the nuclear events. In mitosis, a single division produces two identical daughter cells, each containing 23 pairs of chromosomes. In meiosis a pair of divisions produces four different, haploid gametes, each containing 23 individual chromosomes.

Four spermatids are produced for every primary spermatocyte that enters meiosis. The spermatids remain embedded within sustentacular cells while they mature into a spermatozoon, a process called spermiogenesis.

The sustentacular cells have five important functions:

1. Maintenance of the blood-testis barrier
2. Support of spermatogenesis: Spermatogenesis depends on the stimulation of sustentacular cells by circulating FSH and testosterone
3. Support of  spermiogenesis
4. Secretion of inhibin which depresses the pituitary production of FSH and GnRH. The faster the rate of sperm production, the greater the amount of inhibin secreted.
5.  Secretion of androgen-binding protein (ABP), which binds androgens in the fluid contents of the seminiferous tubules.

Anatomy of a Spermatozoon

Each spermatozoon has a head, neck, middle piece, and a tail.

-         The head is a flattened oval containing densely packed chromosomes. The tip of the head contains the acrosomal cap.

-         A short neck attaches the head to the middle piece, and contains both centrioles of the original spermatid.

        -         The tail is the only example of a flagellum in the human body. A flagellum moves a cell from one place to another.

 Lacking most intracellular structures (endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, inclusions, etc.), the spermatozoon must absorb nutrients from the environment.

 
The Male Reproductive Tract

After detaching from the sustentacular cells, the spermatozoa are carried along fluid currents into the epididymis, an elongate tubule with head, body, and tail regions. The superior head of the epididymis receives spermatozoa via the efferent ducts of the mediastinum of the testis. The body begins distal to the last efferent duct and extends inferiorly along the posterior margin of the testis. Finally, near the inferior border of the testis, the number of convolutions decreases, marking the start of the tail.

The epididymis has three major functions:

1. It monitors and adjusts the composition of the fluid produced by the seminiferous tubules
2. It serves as a recycling center for damaged spermatozoa
3. It stores spermatozoa, and facilitates their functional maturation (a process called capacitation).

 
The Ductus Deferens

The ductus deferens (or vas deferens as you probably know it) begins at the end of the tail of the epididymis and passes through the inguinal canal as one component of the spermatic cord. Near the prostate, it enlarges to form the ampulla. The junction of the base of the seminal vesicle and the ampulla creates the ejaculatory ducts, which empties into the urethra. The ductus deferens functions to transport and store spermatozoa.

The Urethra

The urethra extends from the urinary bladder to the tip of the penis. It can be divided into three regions; the prostatic urethra, membranous urethra, and spongy urethra. The urethra in the male is a passageway used by both the urinary and reproductive systems. (I know, it’s completely natural, but that’s still kinda gross).

The Accessory Glands

 
The accessory glands function to activate and provide nutrients to the spermatozoa and to produce buffers to neutralize the acidity of the urethra and vagina.

Each seminal vesicle is an active secretory gland that contributes about 60 percent of the volume of semen; its secretions are high in fructose, which is easily used to produce ATP by spermatozoa. The spermatozoa become highly active after mixing with the secretions of the seminal vesicles

The prostate gland secretes a weakly acidic fluid (prostatic fluid) that accounts for 20-30 percent of the volume of semen. These secretions contain an antibiotic, seminalplasmin, which may help prevent urinary tract infections in men. (I want to know why we women don’t get to have it).

The paired bulbourethreal glands are located at the base of the penis, covered by the fascia of the urogenital diaphragm. The alkaline mucus secreted by the bulbourethreal glands has lubricating properties.

Semen

A typical ejaculation releases 2-5 ml of semen. The volume of fluid, called an ejaculate, contains:

1. Spermatozoa: A normal a sperm count of 20 to 100 million sperm per milliliter.

2. Seminal fluid:  The seminal fluid is a specific mixture of secretions of the accessory glands and contains important enzymes

3. Enzymes: Several important enzymes are present in the fluid including a protease that may help dissolve mucous secretions in the vagina and seminalplasmin, an antibiotic enzyme that kills a variety of bacteria.

The Penis

The penis is a tubular organ that contains the distal portion of the urethra. The penis can be divided into a root, body (shaft) and glans.

-         The root of the penis is the fixed portion that attaches the penis to the rami of the ischia. This connection occurs  within the urogenital triangle immediately inferior to the pubic symphysis

-         The body (shaft) of the penis is the tubular, movable portion. Masses of erectile tissue are found within the body.

-         The glans of the penis is the expanded distal end that surrounds the external urethral orifice.

The skin overlying the penis resembles that of the scrotum. The prepuce (foreskin) surrounds the tip of the penis. Preputial glands on the inner surface of the prepuce secrete a waxy material known as smegma.

 Most of the body of the penis consists of three masses of erectile tissue. Beneath the superficial fascia, there are two corpora cavernosa and a single corpus spongiosum that surrounds the urethra. When the smooth muscles in the arterial walls relax, the erectile tissue becomes engorged with blood, producing an erection.

Anatomy of the Female Reproductive System

A woman’s reproductive system must produce functional gametes, protect and support a developing embryo, and nourish the newborn infant (we have to do a lot!). Principal structures of the female reproductive system include the ovaries, uterine tubes, uterus, vagina, and external genitalia.
 

The ovaries, uterine tubes, and uterus are enclosed within the broad ligament (an extensive mesentery). The mesovarium supports and stabilized each ovary.

The Ovaries

The ovaries are small, paired organs located near the lateral walls of the pelvic cavity. They are held in position by the ovarian ligament and the suspensory ligament. The ovarian artery and vein enter the ovary at the ovarian hilum. Each ovary is covered by a tunica albuginea (a dense layer of connective tissue).

The Ovarian Cycle and Oogenesis

The production of female gametes, a process called oogenesis, usually occurs on a monthly basis, as part of the ovarian cycle. Here are the steps of the cycle:

1. Formation of Primary Follicles
2. Formation of Secondary Follicles
3. Formation of a Tertiary Follicle
4. Ovulation (stimulation of ovulation is a sudden rise in LH levels)
5. Formation of the Corpus Luteum (which is used to produce progestins)
6. Formation of the Corpus Albicans

The decline in progesterone and estrogen triggers the secretion of GnRH, which in turn triggers a rise in FSH and LH production, and the entire cycle begins again. (There’s a really good picture of this on page 727, figure 27.12).

The hormone estradoil is the most important estrogen, and it is the dominant hormone prior to ovulation. Estrogens have several important functions, including:

1. Stimulating bone and muscle growth
2. Maintaining female secondary sex characteristics
3. Affecting CNS activity, including sex-related behaviors and drives
4. Maintaining the function of the reproductive glands and organs
5. Initiating the repair and growth of the uterine lining

The Uterine Tube

Each uterine tube has four regions:

1. The infundibulum: The end closest to the ovary forms an expanded funnel (or infundibulum), with numerous fingerlike projections that extend into the pelvic cavity.
2. The ampulla: The ampulla is the intermediate portion of the uterine tube
3. The isthmus: The ampulla leads to the isthmus, which is a short segment adjacent to the uterine wall
4. The intramural part: A 1-cm long portion within the wall of the uterus.

Histology of the Uterine Tube

The uterine tube is lined with ciliated and nonciliated simple columnar epithelia cells, which aid in the transport of materials. For fertilization to occur, the ovum must encounter spermatozoa during the first 12-24 hours of its passage from the infundibulum to the uterus. The uterine tube also provides a rich, nutritive environment containing lipids and glycogen.

The Uterus

The uterus provides mechanical protection and nutritional support to the developing embryo.  Normally the uterus bends anteriorally near its base, which is called anteflexion. If the uterus bends backward toward the sacrum, the condition is called retroflexion (which apparently has no clinical significance).

 
The uterus is stabilized by the broad ligament, uterosacral ligaments, round ligaments, and the cardinal ligaments.

The uterine body, or corpus, is the largest region of the uterus. The fundus is the rounded portion of the body superior to the attachment of the uterine tubes. The body ends at a constriction called the isthmus. The cervix is the inferior portion that extends from the isthmus to the vagina. The external os leads to the cervical canal, which leads to the uterine cavity and internal os. The uterine wall can be divided into an inner endometrium, a muscular myometrium, and a superficial perimetrium.

Blood Supply to the Uterus
 

The uterus receives blood from the uterine arteries, which then branch and form extensive interconnections.

The Uterine Cycle

A typical 28-day uterine cycle (or menstrual cycle) begins with the onset of menses and the destruction of the functional zone of the endometrium. This process of menstruation continues from one to seven days. The three phases of the uterine cycle are menses, the proliferative phase, and the secretory phase.

After menses, the proliferative phase begins and the functional zone undergoes repair and thickens. Menstrual activity begins at menarche and continues until menopause.

The Vagina

The vagina is an elastic, muscular tube extending between the uterus and the vestibule, which is a space bounded by the external genitalia. The vagina has three major functions:

1. It serves as a passageway for the elimination of menstrual fluids,
2. receives the penis during sexual intercourse and holds spermatozoa before they pass into the uterus
3. In childbirth, it forms the lower portion of the birth canal.

A thin epithelial fold, the hymen, partially blocks the entrance to the vagina. The vagina is lined by a stratified squamous epithelium which, when relaxed, forms rugae (folds).

The structures of the vulva (pudendum) include the vestibule, labia minora, clitoris, prepuce (hood) and labia majora. The lesser and greater vestibular glands keep the area moistened in and around the vestibule. The fatty mons pubis creates the outer limit of the vulva.

The Mammary Glands

The mammary glands lie in the subcutaneous layer beneath the skin of the chest and are the site of milk production, or lactation. The glandular tissue of the breast consists of secretory lobules. Ducts leaving the lobules converge into a single lactiferous duct and expand near the nipple, forming a lactiferous sinus. The ducts of underlying mammary glands open onto the body surfaces at the nipple. Branches of the internal thoracic artery supply blood to each breast. 

Development of the Mammary Glands during Pregnancy

Mammary glands develop during pregnancy under the influence of PRL and GH from the anterior pituitary, as well as human placental lactogen (HPL) from the placenta.

Pregnancy and the Female Reproductive System

If fertilization occurs, the zygote (fertilized egg) undergoes a series of cell divisions, forming a hollow ball of cells known as a blastocyst. Implantation of the blastocyst occurs in the endometrial wall. The placenta that develops functions as a temporary endocrine organ, producing several important hormones. Human chorionic gonadotropin (HCG) maintains the corpus luteum for several months. By the time the corpus luteum degenerates, the placenta is actively secreting both estrogen and progesterone. The placenta also produces relaxin, which is important for delivery, and human placental lactogen (HPL).

Aging and the Reproductive System

Menopause

Menopause (the time when ovulation and menstruation cease) typically occurs around ages 45-55. Premature menopause occurs before age 40. Production of GnRH, FSH, and LH rises, while circulating concentrations of estrogen and progestins decline. The reduced estrogen concentrations have also been linked to the development of osteoporosis, and a variety of cardiovascular and neural effects, including “hot flashes”, anxiety and depression.

The Male Climacteric

The male climacteric, which occurs between ages 50 and 60, involves a decline in circulating testosterone levels and a rise in FSH and LH levels. Although sperm production continues (men can father children well into their eighties), there is a gradual reduction in sexual activity in older men, which may be linked to declining testosterone levels.

Wow, I did it without making any smart ass comments! Ok, the next chapter is the last one on the exam, and it will be posted soon!!

So, this chapter really doesn’t seem that bad (it’s only like 20 pages) so hopefully the blog will be a little easier to deal with than the last two. Anyway, on to the urinary system!

 
The functions of the urinary system include:

1. Regulating plasma concentrations of sodium, potassium, chloride, calcium and other ions by controlling the quantities lost in the urine

2. Regulating blood volume and pressure by adjusting the volume of water lost and releasing erythropoietin and renin

3. Helping stabilize blood pH

4. Conserving valuable nutrients by preventing their excretion in the urine

5. Eliminating organic waste products, especially nitrogenous wastes such as urea and uric acid, toxic substances, and drugs

6. Synthesizing calcitriol, a hormone derivative of vitamin D3 that stimulates calcium ion absorption by the intestinal epithelium

7. Assisting the liver in detoxifying poisons and, during starvation, deaminating amino acids so that other tissues can break them down

 
The urinary system includes the kidneys, the ureters, the urinary bladder, and the urethra. The kidneys produce urine (a fluid containing water, ions, and soluble compounds); during urination (micturition) urine is forced out of the body.

 
The Kidneys

The kidneys are located on either side of the vertebral column between the last thoracic and third lumbar vertebrae.

The position of the kidneys in the abdominal cavity is maintained by

1. the overlying peritoneum

2. contact with adjacent visceral organs

3. supporting connective tissues.

 
The three concentric layers of connective tissue are:

 - The renal capsule, which covers the outer surface of the organ. It maintains the shape of the kidney and provides mechanical protection.

 - The adipose capsule, which surrounds the renal capsule

 - The renal fascia, which anchors the kidney to surrounding structures. A layer of pararenal fat separates the posterior and lateral portions of the renal fascia from the body wall.

 
The ureter and renal blood vessels are attached to the hilus of the kidney. The inner layer of the renal capsule lines the renal sinus, which is an internal cavity within the kidney.

The kidney is divided into an outer renal cortex, a central renal medulla, and an inner renal sinus. The medulla contains 6-18 renal pyramids, whose tips, or renal papillae, project into the renal sinus. Renal columns composed of cortex separate adjacent pyramids. A renal lobe contains a renal pyramid, the overlying area of renal cortex, and adjacent tissues of the renal columns.

 The kidneys are highly vascularized; they receive 20-25 percent of the total cardiac output. The vasculature of the kidneys includes the renal, segmental, interlobar, arcuate, and interlobular arteries to the afferent arterioles that supply the nephrons. From the nephrons, blood flows into the interlobular, arcuate, interlobar, and renal veins.

Urine production in the kidneys is regulated in part through autoregulation, which involves reflexive changes in the diameters of the arterioles supplying the nephrons. The kidneys and ureters are innervated by renal nerves. Sympathetic activation regulates glomerular blood flow and pressure, stimulates renin release, and accelerates sodium ion and water reabsorption.

The nephron (the basic functional unit in the kidney) consists of a renal tubule that empties into the collecting system. There is an awesome diagram on page 694 on the Anatomy of the Nephron. From the renal corpuscle, the tubular fluid travels through the proximal convoluted tubule (PCT), the loop of Henle (nephron loop), and the distal convoluted tubule (DCT). It then flows through the connecting tubule, collecting duct, and papillary duct to reach the renal minor calyx. Check out page 692 Figure 26.4c, it explains it pretty well.

Roughly 85 percent of the nephrons are cortical nephrons found within the cortex (hence the name cortical nephrons). The loops of Henle are short and the efferent arteriole provides blood to the peritubular capillaries that surround the renal tubules. The juxtamedullary nephrons are closer to the medulla, with their loops of Henle extending deep into the renal pyramids.

 
Nephrons are responsible for

1. production of filtrate

2. reabsorption of organic nutrients

3. reabsorption of water and ions.

 
The parietal epithelium lines the outer wall of the renal corpuscle. Blood arrives via the relatively large afferent arteriole and departs in the relatively small efferent arteriole (back to afferent and efferent again!).

The renal corpuscle contains the capillary knot of the glomerulus and Bowman’s capsule (glomerular capsule). At the glomerulus, podocytes of the visceral epithelium wrap their “feet” around the capillaries. The pedicles of the podocytes are separated by narrow filtration slits. The capsular space separates the parietal and visceral epithelia. The glomerular capillaries are fenestrated capillaries (remember fenestrated capillaries?).

The lamina densa of the basial lamina is unusually thick. Blood arrives at the vascular pole of the renal corpuscle via the afferent arteriole and departs in the efferent arteriole. From the efferent arteriole blood enters the peritubular capillaries and the vasa recta that follow the loops of Henle in the medulla.

Filtration occurs as blood pressure forces fluid and dissolved solutes out of the glomerulus and into the capsular space. The filtration process involves passage across three physical barriers:

1. The capillary endothelium: The glomerular capillaries are fenestrated capillaries, whose openings are small enough to prevent the passage of blood cells, but they are too large to restrict the diffusion of solutes.
2. The basal lamina: The basal lamina that surrounds the capillary endothelium has a lamina densa several times the density and thickness of a typical basal lamina. The lamina densa of the glomerulus restricts the passage of the larger plasma proteins but permits the movement of smaller plasma proteins, nutrients, and ions.
3. The glomerular epithelium: The podocytes have long cellular processes that wrap around the outer surfaces of the basal lamina.

The Proximal Convoluted Tubule

The proximal convoluted tubule (PCT) actively reabsorbs nutrients, ions, plasma proteins, and electrolytes from the tubular fluid.

 
The Loop of Henle

The loop of Henle includes a descending limb and an ascending limb; each limb contains a thick segment and a thin segment. The ascending limb delivers fluid to the distal convoluted tubule (DCT), which actively secretes ions and reabsorbs sodium ions from the urine. Reabsorption in the PCT and the loop of Henle reclaims all of the organic nutrients, 85 percent of the water, and more than 90 percent of the Na and Cl ions.

The Distal Convoluted Tubule

The distal convoluted tubule is an important site for the secretion of ions and other materials and the reabsorption of sodium ions.

The juxtaglomerular appatus is composed of the macula densa, juxta-glomerular cells, and the extraglomerular mesangial cells. The juxtaglomerular apparatus secretes the hormones renin and erythropoietin.

The Collecting System

The DCT opens into the collecting system. The collecting system consists of connecting tubules, collecting ducts, and papillary ducts. In addition to transporting fluid from the nephron to the renal pelvis, the collecting system adjusts the osmotic concentrations and volume.

In a sectional view, the DCT differs from the PCT in these ways:

1. The DCT has a smaller diameter
2. The epithelial cells of the DCT lack microvilli
3. The boundaries between the epithelial cells in the DCT are distinct

Structures for Urine Transport, Storage, and Elimination

Tubular fluid modification and urine production end when the fluid enters the minor calyx in the renal sinus. The rest of the urinary system (the ureters, urinary bladder, and the urethra) is responsible for transporting, storing, and eliminating the urine.

The Ureters

The ureters extend from the renal pelvis to the urinary bladder and are responsible for transporting urine to the bladder. The wall of each ureter consists of an inner mucosal layer, a middle muscular layer, and an outer connective tissue layer. The ureters penetrate the posterior wall of the urinary bladder without entering the peritoneal cavity. They pass through the bladder wall at an oblique angle, and the ureteral opening is slitlike rather than rounded. This shape helps prevent backflow of urine toward the ureter and kidneys when the urinary bladder contracts.

The Urinary Bladder

The urinary bladder is a hollow muscular organ that serves as a temporary storage reservoir for urine. The bladder is stabilized by the median umbilical ligament or urachus and the lateral umbilical ligaments. Internal features include the trigone, the neck, and the internal urethral sphincter. The mucosal lining contains prominent rugae (folds). Contraction of the detrusor muscle compresses the urinary bladder and expels the urine into the urethra.

The Urethra

The urethra extends from the neck of the urinary bladder to the exterior. In the female, the urethra is short and ends in the external urethral orifice (external urethral opening), and in the male, the urethra has prostatic, membranous, and penile sections; the spongy urethra ends at the external urethral orifice. In both sexes, as the urethra passes through the urogenital diaphragm, a circular band of skeletal muscles forms the external urethral sphincter, which is under voluntary control.

 
Histology of the Urethra

The female urethral lining is usually a transitional epithelium near the urinary bladder; the rest is usually a stratified squamous epithelium. The urethral lining of males varies from a transitional epithelium at the urinary bladder, to a stratified, columnar or a pseudostratified epithelium, and then to a stratified squamous epithelium near the external urethral orifice.

 
The Micturition Reflex and Urination

The process of urination is coordinated by the micturition reflex, which is initiated by stretch receptors in the bladder wall. The stretch receptors in the wall of the urinary bladder are stimulated as it fills with urine. Voluntary urination involves coupling this reflex with the voluntary relaxation of the external urethral sphincter.

 
Aging and the Urinary System

 Aging is usually associated with increased kidney problems. Age-related changes in the urinary system include:

1. A declining number of functional nephrons

2. A reduction in glomerular filtration

3. Reduced sensitivity to ADH- Less reabsorption of water and sodium ions occurs as a result; urination becomes more frequent, and daily fluid requirements increase.

4. Problems with the micturition reflex – Several factors are involved in this problem:

a. The sphincter muscles lose muscle tone and become less effective at voluntarily retaining urine. This loss of tone leads to incontinence (which is a slow leakage of urine

b. The ability to control micturition is often lost after a stroke, Alzheimer’s disease, or other CNS problems affecting the cerebral cortex or hypothalamus

c. In males, urinary retention may develop secondary to chronic inflammation of the prostate gland. In this condition swelling and distortion of prostatic tissues compress the prostatic urethra, restricting or preventing the backflow of urine.

 
Ok, so that was actually pretty straightforward. I wish every chapter was that quick!!

The digestive system consists of the muscular tube (called the digestive tract) and various accessory organs. The digestive tract is made up of the oral cavity (mouth), pharynx, esophagus, stomach, small intestine, and large intestine. The accessory organs are the teeth, tongue, and various glandular organs (such as the salivary glands, liver, and pancreas).

 
The digestive functions include:

 1.  Ingestion, which is when foods and liquids enter the digestive tract via the mouth.

2. Mechanical processing ex: squashing ingested solids with the tongue and tearing and crushing with the teeth.

3. Digestion which is the chemical and enzymatic breakdown of complex sugars, lipids, and proteins into small organic molecules.

4. Secretion- digestion usually involves the action of acids, enzymes, and buffers produced by active secretion. Some of these secretions are produced by the lining of the digestive tract, but most are provided by the accessory organs, such as the pancreas.

5. Absorption which is the movement of organic molecules, electrolytes, vitamins, and water across the digestive epithelium and into the interstitial fluid of the digestive tract.

6. Excretion: Waste products are secreted into the digestive tract, primarily by the accessory glands (especially the liver).

7. Compaction: Compaction is the progressive dehydration of indigestible materials and organic wastes prior to elimination from the body. The compacted material is called feces, and the elimination of feces from the body is defecation.

 
The lining of the digestive tract also plays a defensive role by protecting surrounding tissues against:

1. the corrosive effects of digestive acids and enzymes

2. mechanical stresses, such as abrasion

3. pathogens that are either swallowed with food or residing within the digestive tract.

Histological Organization of the Digestive Tract

 
The major layers of the digestive tract include the mucosa, the submucosa, the muscularis externa and the serosa.

 
The inner lining, or mucosa, of the digestive tract is an example of a mucous membrane. The mucosal epithelium may be simple or stratified, depending on the location and stresses involved. The underlying layer of areolar tissue, called the lamina propria, contains blood vessels, sensory nerve endings, lymphatic vessels, smooth muscle fibers, and scattered areas of lymphoid tissue. The lining of the digestive tract contains pleats that allow for expansion.

 The submucosa is a layer of areolar tissue that surrounds the muscularis mucosae. The submucosal plexus innervates the mucosa; it contains sensory neurons, parasympathetic ganglia, and sympathetic postganglionic fibers.

The muscularis externa, which surrounds the submucosa, is a region dominated by smooth muscle fibers. The smooth muscle cells of the digestive tract are capable of plasticity, which is the ability to tolerate extreme stretching. The digestive system contains visceral smooth muscle tissue, in which the muscle cells are arranged in sheets and contain no motor innervation. The presence of pacesetter cells allows for rhythmic waves of contraction that spread through the entire muscular sheet. Pacesetter cells are found in both the muscularis mucosae and muscularis externa.

 The muscularis externa propels materials through the digestive tract through the contractions of peristalsis. Peristalsis consists of waves of muscular contractions that move a bolus (a small oval mass of food) along the length of the digestive tract. (I want to know at what point food becomes a bolus).  

 Most areas of the small intestine and some regions of the large intestine undergo contractions that produce segmentation. These movements churn and fragment the digestive materials, mixing the contents with intestinal secretions. They do not produce net movement in any particular direction.

Both segmentation and peristalsis may be triggered by pacesetter cells, hormones, chemicals, and physical stimulation.

The Peritoneum

The serosa, also known as the visceral peritoneum, is continuous with the parietal peritoneum that lines the inner surfaces of the body wall. Organs of the abdominal cavity may have a variety of relationships with the peritoneum, including intraperitoneal, retroperitoneal, and secondarily retroperitoneal.

Intraperitoneal organs lie within the peritoneal cavity, in that they are covered on all sides by the visceral peritoneum. Examples are the stomach, liver, and ileum.

Retroperitoneal organs are covered by the visceral peritoneum on their anterior surface only, and the organ per se lies outside the peritoneal cavity. Examples include the kidneys, ureters, and abdominal aorta.

Secondarily retroperitoneal organs are organs of the digestive tract that form as intraperitoneal organs but then become retroperitoneal organs. Examples include the pancreas and much of the duodenum.

 
Mesenteries

Fused double sheets of peritoneal membrane called mesenteries suspend portions of the digestive tract. Important mesenteries include the greater omentum, lesser omentum, mesentery proper, transverse mesentery, and sigmoid mesocolon. The ascending colon, descending colon, duodenum, and pancreas are attached to the posterior wall of the abdominopelvic cavity, they are retroperitoneal.

The Oral Cavity

 The functions of the oral cavity include:

1. analysis of potential foods

2. mechanical processing using the teeth, tongue, and palatal surfaces

3. lubrication by mixing with mucus and salivary secretions

4. digestion by salivary enzymes.

 
Structures of the oral cavity include the tongue, salivary glands, and teeth.

Anatomy of the Oral Cavity

I’m not going to go into this one too much, because I think we all pretty much know where our lips and cheeks are, but I’ll go into it a little bit.

The buccal cavity (oral cavity) is lined by the oral mucosa, which is a stratified squamous epithelium. The hard and soft palates form the roof of the oral cavity. The posterior margin of the soft palate supports the dangling uvula and two pairs of muscular pharyngeal arches.

1. The palatoglossal arches extend between the soft palate and the base of the tongue. Each arch consists of a mucous membrane and the underlying palatoglossus muscle and associated tissues.
2. The palatopharyngeal arches extend from the soft palate to the side of the pharynx.

The tongue aids in mechanical processing and manipulation of food as well as sensory analysis. The superior surface (dorsum) of the body of the tongue is covered with papillae. The inferior portion of the tongue contains a thin fold of mucous membrane called the linguinal frenulum, which connects the body of the tongue to the mucosa of the oral floor.  Intrinsic and extrinsic tongue muscles are controlled by the hypoglossal nerve.

There are three types of salivary glands- parotid, sublingual, and submandibular salivary glands:  

 The parotid salivary glands discharge their secretions into the oral cavity. They are the largest salivary glands, irregularly shaped, and their secretions are drained by a parotid duct, which empties into the vestibule at the level of the second upper molar. The parotid salivary glands release salivary amylase, which begins the breakdown of carbohydrates.

 The sublingual salivary glands are covered by the mucous membrane of the floor of the mouth. Sublingual ducts open along either side of the lingual frenulum.

 The submandibular salivary glands are found in the floor of the mouth along the medial surfaces of the mandible inferior to the mylohyoid line. The submandibular ducts open into the mouth on either side of the lingual frenulum immediately posterior to the teeth.

Saliva lubricates the mouth, solubilizes food, dissolves chemicals, flushes the oral surfaces, and helps control bacteria. Salivation is usually controlled by the autonomic nervous system.

The Teeth

 Ok, I have to say it. I hate teeth. Absolutely hate them. I cannot stand to see someone pull out a tooth, or in the movie Cast Away when Tom Hanks had to take out his tooth using an ice skate. That scarred me for life. But, because I’m so dedicated, I’m gonna write about teeth (that, and I want to pass the exam).

Dentin forms the basic structure of a tooth. The crown is coated with enamel, and the root with cementum. The neck marks the boundary between the root and the crown. The periodontal ligament anchors the tooth in an alveolar socket. Mastication (chewing) occurs through the contact of the opposing occlusal surfaces of the teeth.

 
There are four types of teeth, each with specific functions:

1. Incisors are blade-shaped teeth found at the front of the mouth. They’re used for clipping or cutting.
2. The cuspids (or canines) are conical with a sharp ridgeline and a pointed tip. They are used for tearing or slashing.
3. Bicuspids (or premolars) have one or two roots. They have flattened crowns with prominent ridges and are used for crushing, mashing, and grinding.
4. Molars have very large flattened crowns with prominent ridges and typically have three or more roots.

 The first set of teeth to appear are called deciduous teeth (primary, milk, or baby teeth). There are usually 20 deciduous teeth, five on each side of the upper and lower jaws. These teeth then will be replaced with the adult secondary dentition (permanent dentition).

 The upper rows of teeth form a dental arcade with labial, palatal (upper teeth) or lingual (lower teeth), mesial and distal surfaces.

 
Mastication forces the food across the surfaces of the teeth until it forms a bolus that can be swallowed easily.

 
The Pharynx

Skeletal muscles involved with swallowing include the pharyngeal constrictor muscles and the palatopharyngeus, stylopharyngeus, and palatal muscles.

 
Swallowing Process

Deglutition (swallowing) has three phases. The buccal phase begins with the compaction of a bolus and its movement into the pharynx. The pharyngeal phase involves the elevation of the larynx, reflection of the epiglottis, and closure of the glottis. Finally, the esophageal phase involves the opening of the upper esophageal sphincter and peristalsis moving the bolus down the esophagus to the lower esophageal sphincter. Check out page 660 Figure 25.8 for a good diagram on this.

 
The Esophagus

The esophagus is a hollow muscular tube that transports food and liquid to the stomach, through the esophageal hiatus, and opening in the diaphragm. The wall of the esophagus is formed by mucosa, submucosa, muscularis, and adventitia layers.

There is an extremely long list of distinctive features of the esophageal wall on page 661 for anyone interested.

The Stomach

 The stomach has three major functions:

1. bulk storage of ingested matter

2. mechanical breakdown of resistant materials

3. chemical digestion through the disruption of chemical bonds using acids and enzymes.

 
The stomach is divided into four regions: the cardia, the fundus, the body, and the pylorus.

1. The cardia is where the esophagus contacts the medial surface of the stomach. I think it’s neat that it’s named “cardia” because of its proximity to the heart.
2. The region of the stomach superior to the gastroesophageal junction is the fundus, which contacts the inferior and posterior surface of the diaphragm.
3. The area between the fundus and the curve of the J is the body of the stomach. The body is the largest region, and it functions as a mixing tank for ingested food and gastric secretions.
4. The pylorus is the curve of the J. The pylorus is divided into the pyloric antrum (which is connected to the body of the stomach) and the pyloric canal (which is connected to the duodenum). A muscular pyloric sphincter regulates the release of chime from the pyloric orifice into the duodenum.

The mucosa and submucosa are thrown into longitudinal folds, called rugae. The muscularis layer is formed of three bands of smooth muscle; a longitudinal layer, a circular layer, and an inner oblique layer.

 
The mesenteries of the stomach are the greater omentum, which hangs from the greater curvature, and the lesser omentum, which is attached to the lesser curvature.

 
Three branches of the celiac trunk supply blood to the stomach; the left gastric artery, splenic artery, and the common hepatic artery.

1. The left gastric artery supplies blood to the lesser curvature and cardia.
2. The splenic artery supplies the fundus directly, and the greater curvature through the left gastroepiploic artery.
3. The common hepatic artery supplies blood to the lesser and greater curvatures of the pylorus through the right gastric artery, the right gastroepiploic artery, and the gastroduodenal artery. Gastric and gastroepiploic veins drain blood from the stomach into the hepatic portal vein.

 
Simple columnar epithelia line all portions of the stomach. Shallow depressions, called gastric pits, contain the gastric glands of the fundus and body. Parietal cells secrete intrinsic factor and hydrochloric acid. Chief cells secret pepsinogen, which acids in the gastric lumen convert to the enzyme pepsin. G cells of the stomach secret the hormone gastrin.

 The production and secretion of gastric juices are directly controlled by the CNS (the Vagus nerve parasympathetic innervation) and the celiac plexus (sympathetic innervation). The release of the local hormones secretin and cholecystokinin inhibits gastric secretion but stimulates secretion by the pancreas and liver.

The Small Intestine

The small intestine, which includes the duodenum, the jejunum and the ileum, plays the primary role in the digestion and absorption of nutrients. The intestinal lining bears a series of transverse folds called plicae circlares.

The duodenum is the shortest and widest segment of the small intestine. It is connected to the pylorus of the stomach, and the interconnection is guarded by the pyloric sphincter. It is considered a “mixing bowl” that receives chime from the stomach and digestive secretions from the pancreas and liver.

 The duodenojejunal flexure marks the boundary between the duodenum and jejunum (fancy that). The bulk of chemical digestion and nutrient absorption occurs in the jejunum.

The ileum is the third, last, and longest segment of the small intestine. The ileum ends at a sphincter, the ileocecal valve, which controls the flow of materials from the ileum and into the cecum of the large intestine.

The superior mesenteric artery and superior mesenteric vein supply numerous branches to the segments of the small intestine. The mesentery proper supports the branches of the superior mesenteric artery and vein, lymphatics, and nerves that supply the jejunum and ileum.

 The mucosa of the small intestine forms small projections, called intestinal villi, which increase the surface area for absorption. Each villus contains a terminal lymphatic called a lacteal. Pockets called intestinal glands house enteroendocrine, goblet, and stem cells.

The regions of the small intestine have histological specializations that determine their primary functions. The duodenum contains duodenal (Brunner’s) glands that aid in producing mucus. Also, it receives the secretions of the common bile duct and pancreatic duct. The jejunum and ileum contain large groups of aggregated lymphoid nodules (Peyer’s patches) within the lamina propria.

 
Hormonal and CNS controls regulate the secretory output of the small intestine and accessory glands. The secretions of the small intestine are collectively called intestinal juice.

The Large Intestine

 The large intestine (large bowel) begins as a pouch inferior to the terminal portion of the ileum and ends at the anus. The main functions of the large intestine are to

1. reabsorb water and electrolytes and compaction of the intestinal contents into feces

2. absorb vitamins produced by bacterial action

3. store fecal material prior to defecation.

 
The large intestine is divided into three parts: the cecum, the colon, and the rectum.

The cecum collects and stores materials arriving from the ileum. The ileum opens into the cecum at the ileal papilla, with muscles encircling the opening forming the ileocecal valve. A band of mesentery, the mesoappendix, connects the appendix to the ileum and cecum. The appendix functions as part of the lymphatic system.

 
The colon has a larger diameter and a thinner wall than the small intestine. There are several distinctive features of the colon:

1. The wall of the colon forms a series of pouches (or haustra) that permit considerable distention and elongation.
2. Three separate longitudinal ribbons of smooth muscle, the taeniae coli, are visible on the outer surfaces of the colon just beneath the serosa.
3. The serosa of the colon contains numerous teardrop-shaped sacs of fat, called the fatty appendices of the colon, or epiploic appendages.

The colon is subdivided into four regions; ascending, transverse, descending, and sigmoid.

The ascending colon begins at the superior border of the cecum and ascends along the right lateral and posterior wall of the peritoneal cavity to the inferior surface of the liver.

The transverse colon begins at the right colic flexure. It curves anteriorly and crosses the abdomen from right to left. The gastrocolic ligament attaches the transverse colon to the greater curvature of the stomach. Near the spleen, the colon makes a right-angle bend, called the left colic flexure (or splenic flexure) and then proceeds caudally.

The descending colon is firmly attached to the abdominal wall. At the iliac fossa, the descending colon enters an S-shaped segment (the sigmoid colon) at the sigmoid flexure.

 The sigmoid colon is an S-shaped segment of the large intestine that curves posterior to the urinary bladder and is suspended by the sigmoid mesocolon. It then empties into the rectum.

The Rectum

The rectum is an expandable organ for the temporary storage of fecal material. The rectum terminates in the anal canal leading to the anus. Internal and external anal sphincters control the passage of fecal material to the anus. Distention of the rectal wall triggers the defecation reflex.

The major histological features of the large intestine are lack of villi, abundance of goblet cells, and distinctive mucus-secreting intestinal glands. There’s a lot more, it’s on page 673 (this blog is getting to be too long already).

Movement from the cecum to the transverse colon occurs slowly via peristalsis and haustral churning. Movement from the transverse to the sigmoid colon occurs several times each day via mass movements. (Ok, this stuff is just gross. I’m trying really hard not to comment on it, and just type what the book says.)

Distention of the rectal wall from a mass movement may stimulate the conscious desire to relax internal and external anal sphincters to defecate. (I know, if we’re all going to be medical professionals, we have to be mature about this stuff, but ewwwwwwwwwwwwwww!!!)

 
The Liver

The liver is the largest visceral organ, and it is also one of the most versatile organs in the body. The liver is responsible for three major services

1. Metabolic regulation: The liver represents the central clearinghouse for metabolic regulation in the body
2. Hematological regulation: The liver is the largest blood reservoir in the body, and it receives about 25 percent of the cardiac output
3. Synthesis and secretion of bile: Bile is synthesized by liver cells, stored in the gallbladder, and excreted into the lumen of the duodenum. Bile consists of mostly water, with minor amounts of ions, bilirubin, and an assortment of lipids collectively known as bile salts.

This is actually cool: To date, more than 200 different functions have been assigned to the liver. Look at Table 25.1 on page 675 for some of them.

The classic topographical description of the liver has the organ divided into four lobes; the left, right, quadrate and caudate. The gallbladder is located in a fossa within the posterior surface of the right lobe.

The hepatic artery proper and hepatic portal vein supply blood to the liver. Hepatic veins drain blood from the liver and return it to the systemic circuit via the inferior vena cava.

 Liver cells are specialized epithelial cells, called hepatocytes, and in a liver lobule they form a series of irregular plates arranged like the spokes of a wheel.  Kupffer cells (stellate reticuloendothelial cells), are phagocytic cells that reside in the sinusoidal lining.

 The liver lobule is the basic functional unit of the liver. Each lobule is hexagonal in cross section and contains six portal areas, or hepatic triads. A portal area consists of a branch of the hepatic portal vein, a branch of the hepatic artery proper, and a branch of the hepatic (bile) duct. Bile canaliculi (small passageways) carry bile to bile ductules that lead to portal areas. The bile ducts from each lobule unite to from the left and right hepatic ducts, which merge to form the common hepatic duct.

The Gallbladder

The gallbladder is a hollow muscular organ that stores and concentrates bile before excretion in the small intestine. The gallbladder has two major functions, bile storage and bile modification. Bile salts break apart large drops of lipids and make them accessible to digestive enzymes. Bile ejection occurs under stimulation of cholecytstokinin (CCK).

The gallbladder is divided into three regions, the fundus, body, and neck. The cystic duct leads from the gallbladder to merge with the common hepatic duct to form the common bile duct.

Ok, here’s a question for everyone (like one of those critical thinking questions at the end of the chapters). I don’t have a gallbladder, so how does my body deal with bile storage and bile modification? (The answer is actually in the book).

 
The Pancreas

The pancreas lies posterior to the stomach, extending laterally from the duodenum toward the spleen. It is divided into head, body, and tail regions. The pancreatic duct penetrates the wall of the duodenum. Within each lobule, ducts branch repeatedly before ending in the pancreatic acini (blind pockets).

Pancreatic tissue consists of exocrine and endocrine portions. The bulk of the organ is exocrine in function, as the pancreatic acini secret water, ions, and digestive enzymes into the small intestine.

Pancreatic enzymes include lipases, carbohydrases, nucleases, and proteolytic enzymes. Lipases digest lipids, carbohydrases (like pancreatic amylase) digest sugar and starches, nucleases attack nucleic acids, and proteolytic enzymes break proteins apart.

The major hormones produced by the endocrine portion are insulin and glucagons.

 
Aging and the Digestive System

Normal digestion and absorption occur in elderly individuals; however changes in the digestive system reflect age-related changes in other body systems. The changes are:

1. The rate of epithelial stem cell division declines
2. Smooth muscle tone decreases
3. The effects of cumulative damage become apparent (one of the obvious changes is the gradual loss of teeth due to decay or gingivitis).
4. Cancer rates increase
5. Changes in other systems have direct or indirect effects on the digestive system

 
So I tried really hard not to make any comments in this blog, because I figured if I started, I’d make really immature jokes. I’m going to try very hard to be this mature for the reproductive system, but I’m not making any promises…

I’d like to start out by saying I hope everyone had a wonderful Thanksgiving and you’re enjoying your break! Make sure you don’t do TOO much studying, but incase you decide you feel inspired to do some Anatomy, here’s a blog on the respiratory system!!

 
The respiratory system is made up of the nose, nasal cavity and sinuses, pharynx, larynx (which is your voice box), trachea (your windpipe) and conducting passageways leading to the exchange surfaces of the lungs.

 
The respiratory tract consists of the airways that carry air to and from these surfaces. The respiratory tract can be divided into a conducting portion, which extends from the entrance to the nasal cavity to the bronchioles, and a respiratory portion, which includes the respiratory bronchioles and the alveoli. (Alveoli is my new favorite word).

The upper respiratory system consists of the nose, nasal cavity, paranasal sinuses, and pharynx. Ok, this comes up a lot, so know that these passageways filter, warm, and humidify the air, protecting the more delicate conduction and exchange surfaces of the lower respiratory system from debris, pathogens, and environmental extremes.

 The lower respiratory system includes the larynx, trachea, lungs, bronchi, and alveoli. Yes. That was exciting.

Functions of the Respiratory System

 The respiratory system does all of the following:

1. Provides an extensive area for gas exchange between air and circulating blood
2. Moves air to and from exchange surfaces of the lungs
3. Protects respiratory surfaces from dehydration, temperature changes, and other environmental variations
4. Defends the respiratory system and other tissues from pathogens
5. Permits vocal communication
6. Assisting in the regulation of blood volume, blood pressure, and the control of body fluid pH

The respiratory system needs help to do all this stuff. It relies on cooperation of the cardiovascular and lymphatic systems, selected skeletal muscles, and the nervous system.

The respiratory epithelium lines the conducting portions of the respiratory system down to the level of the smallest bronchioles. The respiratory epithelium consists of pseudostratified, ciliated, columnar epithelium with numerous goblet cells. (Ok, seriously, what was up with that sentence?)  The respiratory epithelium produces mucus that traps incoming particles. In the nasal cavity, cilia sweep any debris trapped in mucus or microorganisms toward the pharynx, where it will be swallowed and exposed to the acids and enzymes of the stomach. (The debris just doesn’t stand a chance).

The respiratory defense system includes the mucus escalator (which washes particles toward the stomach), alveolar macrophages, hairs, and cilia.

 The book is saying it again, so I’ll say it again. Filtration, warming and humidification of inhaled air occurs throughout the conducting portion of the respiratory system, but the greatest changes occur within the nasal cavity.

 
The Nose and Nasal Cavity

 
The nose is the primary passageway for air entering the respiratory system. Air normally enters the respiratory system via the paired external nares, which open into the nasal cavity. The nasal vestibule (entryway) of the nose is guarded by hairs that screen out large particles (even bugs! Look, it says it on page 626).

 
The nasal septum separates the right and left portions of the nasal cavity. The bony portion of the nasal septum is formed by the fusion of the perpendicular plate of the ethmoid and the plate of the vomer. The anterior portion of the nasal septum is formed of hyaline cartilage. This cartilaginous (anyone play Scrabble? Can you use that as a word?)  plate supports the bridge (or dorsum of the nose) and apex (or tip) of the nose.

Incoming air flows through the superior, middle, or inferior meatuses (which are actually narrow grooves instead of open passageways) and the incoming air bounces off the conchal surfaces and churns around “like water flowing over rapids”. The book can be so poetic sometimes.

 The bony hard palate, formed by the maxillary and palatine bones, forms the floor of the nasal cavity and separates the oral and nasal cavity. The fleshy soft palate extends posterior to the hard palate, and separates the superior nasopharynx and the rest of the pharynx. The connections between the nasal cavity and nasopharynx represent the internal nares.

 
The Pharynx

The nose, mouth, and throat connect to each other by a common passageway or chamber, which is known as the pharynx. The pharynx is shared by the digestive and respiratory systems. The pharynx is divided into three regions, the nasopharynx, the oropharynx, and the laryngopharynx.

The nasopharynx is the superior portion of the pharynx. The pharyngeal tonsil is located on the posterior wall of the nasopharynx; the lateral walls contain the openings of the auditory tubes.

 The oropharynx extends between the soft palate and the base of the tongue at the level of the hyoid bone. The posterior margin of the soft palate supports the dangling uvula and two pairs of muscular pharyngeal arches. On either side a palatine tonsil lies between an anterior palatoglossal arch and a posterior palatopharyngeal arch. A curving line that connects the palatoglossal arches and uvula forms the boundaries of the fauces, which is the passageway between the oral cavity and the oropharynx.

 The laryngopharynx includes the narrow zone between the hyoid and the entrance to the esophagus. The laryngopharynx is the most inferior part of the pharynx, and (like the oropharynx) it is lined by a stratified squamous epithelium that can resist mechanical abrasion, chemical attack, and pathogenic invasion.

The Larynx

 Inhaled air passes through the glottis en route to the lungs; the larynx surrounds and protects the glottis. There are three large unpaired cartilages that form the body of the larynx, the thyroid cartilage, the cricoid cartilage, and the epiglottis.

 
The thyroid cartilage is the largest laryngeal cartilage. The anterior surface of the cartilage has a thick ridge called the laryngeal prominence. The thyroid cartilage is also referred to as the Adam’s apple.

 The cricoid cartilage is a complete ring whose posterior portion is greatly expanded, providing support in the absence of the thyroid cartilage. The cricoid and thyroid cartilages protect the glottis and the entrance to the trachea, and their broad surfaces provide sites for the attachment of important laryngeal muscles and ligaments.

 The epiglottis projects into the pharynx. During swallowing, the larynx is elevated, and the epiglottis folds back over the glottis, preventing the entry of liquids or solid food into the respiratory passageways.

 
The larynx also contains three pairs of smaller cartilages; the arytenoids, corniculate, and cuneiform cartilages.

The paired arytenoid cartilages articulate with the superior border of the enlarged portion of the cricoid cartilage.

 The corniculate cartilages articulate with the arytenoid cartilages. The corniculate and arytenoid cartilages are involved with the opening and closing of the glottis and the production of sound.

Cuneiform cartilages lie within the aryepiglottic fold that extends between the lateral aspect of each arytenoids cartilage and the epiglottis.

 A series of intrinsic ligaments binds all nine cartilages together to form the larynx. Extrinsic ligaments attach the thyroid cartilage to the hyoid bone and the cricoid cartilage to the trachea.

 
Two pairs of folds span the glottal opening; the relatively inelastic vestibular folds and the more delicate and highly elastic vocal folds. Air passing through the glottis vibrates the vocal folds and produces sound waves. The intrinsic laryngeal muscles regulate tension in the vocal folds and open and close the glottis. The extrinsic laryngeal musculature positions and stabilizes the larynx. During swallowing, both sets of muscles help to prevent particles from entering the glottis. Check out page 630 for a cool description of swallowing.
 

The Trachea

The trachea (windpipe) extends from the sixth cervical vertebra to the fifth thoracic vertebra, where it branches to form the right and left primary bronchi. The lining of the trachea consists of respiratory epithelium overlying a layer of loose connective tissue called the lamina propria.

A thick layer of connective tissue, known as the submucosa, surrounds the mucosa. It contains C-shaped tracheal cartilages that stiffen the tracheal walls and protect the airway. The posterior tracheal wall can distort to permit large masses of food to move along the esophagus.

 
The Primary Bronchi

 The trachea branches within the mediastinum to form the right and left primary bronchi. The left and right primary bronchi are outside the lungs and are called extrapulmonary bronchi. An internal ridge, the carina, lies between the entrances to the two primary bronchi.

The right primary bronchus supplies the right lung, and the left supplies the left lung. The right primary bronchus has a larger diameter than the left, and it descends toward the lung at a steeper angle. Because of this, foreign objects that enter the trachea usually become lodged in the right bronchus instead of the left one. The primary bronchi and their branches form the bronchial tree. Each bronchus enters a lung at the hilus. The root of the lung is a connective tissue mass including the bronchus, pulmonary vessels, and nerves.

 
The Lungs

The left and right lungs are situated in the left and right pleural cavities. Each lung is a blunt cone with the tip, or apex, pointing superiorly. The apex on each side extends into the base of the neck above the first rib. The broad, concave inferior portion, or base, of each lung rests on the superior surface of the diaphragm.

 
The lobes of the lungs are separated by fissures.  The right lung has three lobes; superior, middle, and inferior. The left lung only has two lobes, superior and inferior. There is a great picture of this on page 633. The right lung is broader than the left because most of the heart and great vessels project into the left pleural cavity. However, the left lung is longer than the right lung, because the diaphragm rises on the right side to accommodate the mass of the liver.

 
The costal surface of the lung follows the inner contours of the rib cage. The mediastinal surface contains a hilus, and the left lung bears the cardiac impression. In an anterior view, the medial margin of the right lung forms a vertical line, whereas the medial margin of the left lung bears a concavity, called the cardiac notch.

The connective tissues of the root extend into the parenchyma of the lung as a series of trabeculae (partitions). These branches form septa that divide the lung into lobules, each supplied by tributaries of the pulmonary arteries, pulmonary veins, and respiratory passageways.

Extrapulmonary bronchi (left and right primary bronchi) are outside the lung tissue. Intrapulmonary bronchi (branches within the lung) are surrounded by bands of smooth muscle. The smooth muscle can contract to constrict size and limit air. Each primary bronchus divides to form secondary bronchi (AKA lobular bronchi). Secondary bronchi then branch to form tertiary bronchi, or segmental bronchi.

 Each lung is further divided into smaller units called bronchopulmonary segments. These segments are named according to the associated tertiary bronchi. The right lung contains 10 and the left lung usually contains 8-9 bronchopulmonary segments.

 Within the bronchopulmonary segments each tertiary bronchus ultimately gives rise to 50-80 terminal bronchioles that supply individual lobules.

Alveolar Ducts and Alveoli

The respiratory bronchioles open into alveolar ducts; many alveoli are interconnected at each duct. These passageways end at alveolar sacs, which are common chambers connected to several individual alveoli. The respiratory membrane (alveolar lining) consists of a simple squamous epithelium of squamous alveolar cells (Type I cells). These cells are unusually thin and delicate.  Septal cells (Type II cells) scattered in it produce an oily secretion (known as surfactant) that keeps the alveoli from collapsing. Alveolar macrophages (dust cells) patrol the epithelium and engulf foreign particles.

The Blood Supply to the Lungs

 The respiratory-exchange surfaces are extensively connected to the circulatory system via the vessels of the pulmonary circuit. Check out page 637 for more on the blood supply.

 
The Pleural Cavities and Pleural Membranes

Each lung occupies a single pleural cavity lined by pleura (which is a serous membrane).  The pleural membrane consists of two continuous layers. The parietal pleura covers the inner surface of the thoracic wall and extends over the diaphragm and mediastinum. The visceral pleura covers the outer surfaces of the lungs, extending into the fissures between the lobes. Pleural fluid is secreted by both pleural membranes. Pleural fluid gives a moist, slippery coating that provides lubrication, thereby reducing friction between the parietal and visceral surfaces during breathing.

 
Pulmonary ventilation (or breathing) is the movement of air into and out of the lungs. The function of pulmonary ventilation is to maintain adequate alveolar ventilation, the movement of air into and out of the alveoli. Alveolar ventilation prevents the buildup of carbon dioxide in the alveoli and ensures a continual supply of oxygen that keeps pace with absorption by the bloodstream.

Respiratory Muscles

 
The most important respiratory muscles are the diaphragm and the external and internal intercostals muscles. Contraction of the diaphragm increases the volume of the thoracic cavity; the external intercostals may assist in respiration by elevating the ribs; the internal intercostals depress the ribs and reduce the width of the thoracic cavity, thereby contributing to expiration. The accessory respiratory muscles become active when the depth and frequency of respiration must be increased markedly (I like that word. Markedly). Accessory muscles include the sternocleidomastoid, serratus anterior, transverus thoracis, scalene, pectoralis minor, oblique and rectus abdominus muscles.

 
Respiratory Movements

Respiratory movements can be classified as either eupnea or hyperpnea (depending on whether expiration is passive or active).

In eupnea (or quiet breathing), inspiration involved muscular contractions, but expiration is a passive process. During quiet breathing, expansion of the lungs stretches their elastic fibers. Eupnea may involve diaphragmatic breathing or costal breathing.

During diaphragmatic breathing (or deep breathing), contraction of the diaphragm provides the necessary change in thoracic volume. In costal breathing (or shallow breathing) the thoracic volume changes because the rib cage changes shape.

 Hyperpnea (or forced breathing) involves active inspiratory and expiratory movements.

Respiratory Changes at Birth

I don’t usually go into what happens before birth, but I thought this was pretty cool:
Before delivery the fetal lungs are fluid-filled and collapsed. At the first breath, the lungs inflate and never collapse completely thereafter.

The respiratory centers are three pairs of nuclei in the reticular formation of the pons and medulla oblongata. These nuclei regulate the activities of the respiratory muscles by adjusting the frequency and depth of pulmonary ventilation.

The respiratory rhythmicity center sets the pace for respiration. It can be subdivided into dorsal respiratory group (DRG) and a ventral respiratory group (VRG).

The apneustic center causes strong, sustained inspiratory movements, and the pneumotaxic center inhibits the apneustic center and the inspiratory center in the medulla oblongata.

Normal breathing occurs automatically, without conscious control. Three different reflexes are involved in the regulation of respiration:

1. Mechanoreceptor reflexes respond to changes in the volume of the lungs or to changes in arterial blood pressure
2. Chemoreceptor reflexes respond to changes in the PCO2, pH and P02 of the blood and cerebrospinal fluid
3. Protective reflexes respond to physical injury or irritation of the respiratory tract

 
Conscious and unconscious thought processes can also control respiratory activity by affecting the respiratory centers or controlling the respiratory muscles.

 Aging and the Respiratory System

 The respiratory system is generally less efficient in the elderly because

1. With increasing age, elastic tissue deteriorates though the body. This deterioration reduces the lungs’ ability to inflate and deflate.
2. Movements of the chest cage are restricted by arthritic changes and decreased flexibility of costal cartilages.
3.  Some degree of emphysema is normally found in individuals aged 50-70. On average, roughly 1 square foot of respiratory membrane is lost each year after age 30. However, the extent varies widely depending on lifetime exposure to cigarette smoke and other respiratory irritants.

Well, there it is, the respiratory system. The next chapter is going to be even more fun…

The Lymphatic System

The cells, tissues, and organs of the lymphatic system play a central role in the body's defenses against viruses, bacteria, and other microorganisms.

The lymphatic system includes a network of lymphatic vessels that carry lymph. Lymphatic vessels originate in peripheral tissues and deliver lymph into the venous system.

Lymph consists of:

1. Interstitial fluid, which resembles blood plasma, but with a lower concentration of proteins
2. Lymphocytes, which are cells responsible for the immune response
3. Macrophages of various types.

Functions of the Lymphatic System

The primary functions of the lymphatic system are:

1. Producing, maintaining, and distributing lymphocytes. Lymphocytes are cells that attack invading pathogens, abnormal cells, and foreign proteins.

2. Maintain blood volume and eliminate local variations in the composition of the interstitial fluid.

3. Providing an alternate route for the transport of hormones, nutrients, and waste products.

Structure of Lymphatic Vessels

Lymphatic Capillaries

Lymphatic vessels, or lymphatics, carry lymph from peripheral tissues to the venous system.

Lymphatic capillaries differ from vascular capillaries in several ways:

1. They are larger both in diameter and in sectional view
2. They have thinner walls because their endothelial cells lack a continuous basal lamina.
3. They often have a flat or irregular outline, in part because the walls are too thin to hold their shape when the already low lymph pressure disappears entirely.
4. Their endothelial cells overlap instead of being tightly bound to one another.

The endothelial cells of a lymphatic capillary overlap to act as one-way valve preventing fluid from returning to the intercellular spaces.

Valves of Lymphatic Vessels

Lymphatics contain numerous internal valves to prevent backflow of lymph.

If a lymphatic vessel is compressed or blocked or its valves are damaged, lymph drainage slows or ceases in the affected area. When fluid continues to leave the vascular capillaries in that region but the lymphatic system is no longer able to remove it, the interstitial fluid volume and pressure gradually increase. The affected tissues become distended and swollen, and this is called lymphedema.

Major Lymph-Collecting Vessels

Two sets of lymphatic vessels collect blood from the lymphatic capillaries: the superficial lymphatics and the deep lymphatics.

Superficial lymphatics travel with superficial veins and are found in the following locations:

1. The subcutaneous layer next to the skin
2. The loose connective tissues of the mucous membranes lining the digestive, respiratory, urinary, and reproductive tracts
3. The loose, connective tissues of the serous membranes lining the pleural, pericardial, and peritoneal cavities

Deep lymphatics are large lymphatic vessels that accompany the deep arteries and veins. These lymphatic vessels collect lymph from skeletal muscles and other organs of the neck, limbs, and trunk, as well as visceral organs in the thoracic and abdominopelvic cavities.

Within the trunk, superficial and deep lymphatics converge to form the larger vessels called lymphatic trunks. The lymphatic trunks are:

1. Lumbar trunks
2. Intestinal trunks
3. Bronchomediastinal trunks
4. Subclavian trunks
5. Jugular trunks

The lymphatic trunks in turn empty into two large collecting vessels, the lymphatic ducts, that deliver lymph into the thoracic duct and the right lymphatic duct.

Lymphocytes

Lymphocytes are the primary cells of the lymphatic system, and they are responsible for specific immunity. They respond to the presence of invading organisms (such as bacteria and viruses), abnormal body cells (such as virus-infected cells or cancer cells) and foreign proteins (like the toxins released by some bacteria. Lymphocytes attempt to eliminate these threats or render them harmless by a combination of physical and chemical attack

Types of Lymphocytes

There are three different classes of lymphocytes:
T cells (thymus-dependent)
B cells (bone marrow-derived)
NK cells (natural killer)

Cytotoxic T cells attack foreign cells or body cells infected by viruses; they provide cell-mediated immunity. Regulatory T cells (helper and suppressor) regulate and coordinate the immune response while memory T cells remain "on reserve". They are called memory T cells because they only become activated if the same antigen appears in the body at a later date.

B cells can differentiate into plasma cells which produce and secrete antibodies that react with specific chemical targets or antigens. Antigens are usually associated with pathogens, parts or products of pathogens, or other foreign compounds. Antibodies in body fluids are called immunoglobulins. B cells are responsible for antibody-mediated immunity (or humoral immunity).

NK cells (AKA large granular lymphocytes) attack foreign cells, normal cells infected with viruses, and cancer cells. They provide immunological surveillance by continually policing peripheral tissues.

Lymphocytes and the Immune Response

The goal of the immune response is the destruction or inactivation of pathogens, abnormal cells, and foreign molecules such as toxins.

The body has two different ways of doing this:

1. Direct attack by activated T cells (cell-mediated immunity)
2. Attack by circulating antibodies released by the plasma cells derived from activated B cells (antibody-mediated immunity)

Antigens are engulfed by macrophages, which then present the antigen to T cells so they can begin differentiating. The millions of different lymphocytes, which retain the ability to divide, allow the body to be prepared for any antigen. The ability to recognize antigens is called immunocompetence.

Lymphopoiesis: Lymphocyte Production

Lymphopoiesis occurs in the bone marrow and the thymus.

Hemocytoblasts in the bone marrow produce lymphocytic stem cells with two distinct fates (that sounds so dramatic). One group remains in the bone marrow. These stem cells divide to produce NK cells and B cells, which gain immunocompetence and migrate into peripheral tissues. The second group of stem cells migrates to the thymus. Under the influence of the thymic hormones these stem cells divide repeatedly, producing daughter cells that undergo functional maturation into T cells.

Lymphocytes continually migrate in and out of the blood through the lymphoid tissues and organs and, in general, have relatively long life spans.

Lymphoid Tissues

Lymphoid tissues are connective tissues dominated by lymphocytes. In a lymphoid nodule, the lymphocytes are densely packed in an area of loose connective tissue of the mucous membranes lining the respiratory, digestive, urinary, and reproductive tracts.

The digestive tract has an extensive array of lymphoid nodules collectively known as the mucosa-associated lymphatic tissue (MALT).

Large nodules in the wall of the pharynx are called tonsils. The lymphocytes aggregated in tonsils gather and remove pathogens that enter the pharynx in either inspired air or food. There are usually five tonsils:

1. a single pharyngeal tonsil (often called adenoids) located in the posterior superior wall of the nasopharynx.

2. a pair of palatine tonsil, located at the posterior margin of the oral cavity along the boundary of the pharynx to the soft palate

3. a pair of lingual tonsil, which are not visible because they are located at the base of the tongue

Important lymphoid nodules are aggregated lymphoid nodules beneath the lining of the intestine, the appendix, and the tonsils in the walls of the pharynx.

Lymphoid Organs

Important lymphoid organs include the lymph nodes, the thymus, and the spleen.

Lymph Nodes

Lymph nodes are encapsulated masses of lymphoid tissues. The shape of a typical lymph node resembles a lima bean (yum). Blood vessels and nerves attach to the lymph node at the indentation, or hilus.

The deep cortex is dominated by T cells; the outer cortex and medulla contain B cells arranged in medullary cords. Lymph glands are the largest lymph nodes found where peripheral lymphatics connect with the trunk.

The Distribution of Lymphoid Tissues and Lymph Nodes

Lymphoid tissues and nodes are located in areas particularly susceptible to injury or invasion by microorganisms.

- The cervical lymph nodes monitor lymph originating in the head and neck.
- The axillary lymph nodes filter lymph arriving at the trunk from the upper limbs (for us women, the axillary nodes also drain lymph from the mammary glands).
- The popliteal lymph nodes filter lymph after arriving at the thigh from the leg.
- The inguinal lymph nodes monitor lymph arriving at the trunk from the lower limbs.
- The thoracic lymph nodes receive lymph from the lungs, respiratory passageways, and mediastinal structures.
- The abdominal lymph nodes filter lymph arriving from the urinary and reproductive systems.
- The intestinal lymph nodes (the lymphoid tissue of Peyer's patches) and mesenterial lymph nodes receive lymph originating from the digestive tract.

The Thymus

The thymus lies posterior to the manubrium in the superior mediastinum. The capsule that covers the thymus divides it into two thymic lobes. Fibrous partitions (or septa) extend from the capsule to divide the lobes into lobules. Each lobe consists of a dense outer cortex and a somewhat diffuse, paler central medulla.

Epithelial cells scattered among the lymphocytes produce thymic hormones. These hormones promote the differentiation of T cells. The blood-thymus barrier does not allow free exchange between the interstitial fluid and the circulation protecting the T cells from being prematurely activated. After puberty the thymus gradually decreases in size, a process called involution.

The Spleen

The adult spleen contains the largest mass of lymphoid tissue in the body.

The functions of the spleen include:

1. The removal of abnormal blood cells and other blood components through phagocytosis
2. The storage of iron recycled from broken down red blood cells
3. The initiation of immune responses by B cells and T cells in response to antigens in the circulating blood.

The diaphragmatic surface of the spleen lies against the diaphragm; the visceral surface is against the stomach and kidney and contains a groove called the hilus. The cellular components form the pulp of the spleen. Red pulp contains large numbers of RBCs and areas of white pulp resemble lymphatic nodules. Lymphocytes are scattered throughout the red pulp and the region surrounding the white pulp the has a high concentration of macrophages.

Aging and the Lymphatic System

When a person gets older, the lymphatic system becomes less effective at combating disease. T cells become less responsive to antigens; as a result, fewer cytotoxic T cells respond to an infection. Because the number of helper T cells is also reduced B cells are less responsive, and antibody levels do not rise as quickly after antigen exposure. All this means an increased susceptibility to viral and bacterial infection.
 
Ok, everyone, that's it! All the chapters that will be on the exam. Make sure you gets a good night's sleep tomorrow night, don't stay up too late studying! And of course, break a leg!

Here’s a quick summary on what we’ve learned so far about the cardiovascular system:  

The cardiovascular system is a closed system that circulates blood throughout the body. There are two groups of blood vessels: one supplies the lungs (called the pulmonary circuit) and the other supplies the rest of the body (the systemic circuit). Blood is pumped from the heart into both the pulmonary and systemic (aortic) trunks simultaneously. The relatively small pulmonary circuit begins at the pulmonary valve and ends at the entrance to the left atrium. Pulmonary arteries that branch from the pulmonary trunk carry blood to the lungs for gas exchange. The systemic circuit begins at the aortic valve and ends at the entrance to the right atrium. Systemic arteries branch from the aorta and distribute blood to all other organs for nutrient, gas and waste exchange.  
We’re now going to be looking at the histological and anatomical organization of arteries, capillaries, and veins. Then we’ll look at the major blood vessels and circulatory routes of the cardiovascular system.

(Side note: I’ve read through and outlined this chapter, and again it’s just one of those chapters where I have to list stuff.)
 
 Histological Organization of Blood Vessels

The walls of arteries and veins contain three distinct layers:

1. The inner tunica intima (or tunica interna)

2. A middle tunica media

3.  An outer tunica externa (or tunica adventitia).  

The tunica intima is the innermost layer of a blood vessel. This layer has the endothelial lining of the vessel and an underlying layer of connective tissue containing variable amounts of elastic fibers. In arteries the outer margin of the tunica intima contains a thick layer of elastic fibers called the internal elastic membrane. In the largest arteries, the connective tissue is more extensive and the tunica intima is thicker than in smaller arteries.
 
The tunica media is the middle layer, and it contains concentric sheets of smooth muscle tissue in a framework of loose connective tissue. The smooth muscle fibers of the tunica media encircle the lumen of the blood vessel. When stimulated by sympathetic activation, these smooth muscles may constrict and reduce the diameter of the blood vessel, this is called vasoconstriction. Vasodilation is the relaxation of the smooth muscles which increases the diameter of the lumen.  

Arteries have a thin band of elastic fibers, the external elastic membrane, which is located between the tunica media and tunica externa.
 
The outer tunica externa (or tunica adventitia) forms a connective tissue sheath around the vessel. This layer is very thick, composed chiefly of collagen fibers, with scattered bands of elastic fibers.
 
Their layered walls give arteries and veins considerable strength.
 
 Distinguishing Arteries from Veins

    1. In general, when comparing two adjacent vessels, the walls of arteries are thicker than those of veins, the tunica media of an artery contains more smooth muscle and elastic fibers than does that of a vein. These contractile and elastic components resist the pressure generated by the heart as it forces blood into the circuit.

     2.   When not opposed in blood pressure, arterial walls contract. During dissection or in a sectional view, arteries appear smaller than the corresponding veins. Because the walls of the arteries are relatively thick and strong, they retain their circular shape in section. Cut veins tend to collapse, and in section they often look flattened or grossly distorted.

            3.  The endothelial lining of an artery cannot contract, so when an artery constricts, the endothelium             is thrown into folds that give  arterial sections a pleated appearance. The lining of a vein does not                  have these folds.
 
  (I'm sorry about the spacing on this, I have no idea why livejournal is throwing spaces in #3. I've tried to fix it for 20 mins and it's just not working).
Arteries

Elastic arteries (or conducting arteries) are large vessels with diameters of up to 2.5 cm. They transport large volumes of blood away from the heart. They are also able to stretch and recoil with pressure changes. During ventricular systole, pressures rise rapidly and the elastic arteries are stretched, whereas during ventricular diastole, blood pressure within the arterial system falls, and the elastic fibers recoil to their original dimensions.
 
Muscular arteries (AKA distribution arteries or medium-sized arteries) transport blood to the body’s skeletal muscle and internal organs. They have a thicker tunica media with a greater percentage of smooth muscle fibers than those in the elastic arteries. The external carotid artery of the neck, the brachial arteries of the arms, the femoral arteries of the thighs, and the mesenteric arteries of the abdomen are all muscular arteries. The sympathetic division of the ANS can control the diameter of each of these arteries. By constricting (vasoconstriction) or relaxing (vasodilation) the smooth muscle in the tunica media, the ANS can regulate the blood flow to each organ independently.
 
Arterioles
 
Arterioles are considerably smaller than the muscular arteries. Arterioles have an average diameter of 30 um. The smaller muscular arteries and arterioles change their diameter in response to local conditions or to sympathetic or endocrine stimulation.
 
Capillaries
 
Capillaries are the smallest and most delicate blood vessels. They are VERY THIN. They are important functionally because they are the only blood vessels whose walls permit exchange between the blood and the surrounding interstitial fluids. Because the walls are relatively thin, the diffusion distances are small and exchange can occur quickly. Blood also flows slowly through capillaries, allowing sufficient time for diffusion or active transport of materials across the capillary walls.

Capillaries may be continuous (the endothelium is a complete lining) or fenestrated (the endothelium contains “windows”). Fenestrated capillary walls look like Swiss cheese (I just think that’s cool).

Sinusoids are specialized fenestrated capillaries found in selected tissues (such as the liver, bone marrow, and adrenal glands) that allow very slow blood flow.

Four basic mechanisms are responsible for the exchange of materials across the walls of capillaries and sinusoids:

1. Diffusion across the capillary endothelial cells (lipid-soluble materials, gases, and water by osmosis)
2. Diffusion through gaps between adjacent endothelial cells (water and small solutes; larger solutes in the case of sinusoids)
3. Diffusion through the pores in fenestrated capillaries (water and solutes)
4. Vesicular transport by endothelial cells (endocytosis at luminal side, exocytosis at basil side), water, and specific bound and unbound solutes

Capillaries form interconnected networks called capillary beds (capillary plexuses). A precapillary sphincter (band of smooth muscle) adjusts the blood flow into each capillary. (Ok, I know we’re supposed to be mature college students, but does anyone remember Wayne’s World? Remember the sphincter joke? That’s what I think of every time I hear that word).

 Anyway, central (or preferred) channels provide the means of arteriole-venule communication. A metarteriole is the arteriolar segment of the channel. The entire capillary plexus may be bypassed by blood flow through arteriovenous anastomoses or via central channels within the capillary plexus.  

Veins collect deoxygenated blood from the tissues and organs and return it to the heart. Venules (the smallest veins) collect blood from the capillaries and merge into medium-sized veins, and then large veins. Large veins include the great veins, the superior and inferior vena cavae, and their tributaries within the abdominopelvic and thoracic cavities. The walls of veins are thinner and less elastic than those of corresponding arteries because the blood pressure in veins is lower than that in arteries. Valves in veins prevent the backflow of blood.
 
 The Distribution of Blood
 
 While the heart, arteries, and capillaries usually contain about 30-35 percent of the blood volume, most of the blood volume is in the venous system (65-70 percent). Peripheral venoconstriction helps maintain adequate blood volume in the arterial system after a hemorrhage. The venous reserve, which is the extra blood in the venous system that can be distributed within the arterial system, normally accounts for up to 21 percent of the total blood volume. (There’s a really cool pie chart on page 572 that shows the distribution).
 
 Blood Vessel Distribution
 
Again, the blood vessels of the body can be divided into those of the pulmonary circuit (between the heart and lungs) and the systemic circuit (from the heart to all organs and tissues). There are three important functional patterns to know about the distribution:

1. The peripheral distribution of arteries and veins on the left and right sides is usually identical except near the heart, where the largest vessels connect to the atria or ventricles.
2. A single vessel may have several different names as it crosses specific anatomical boundaries, making accurate anatomical descriptions possible when the vessel extends far into the periphery.
3. Arteries and veins often make anastomotic connections that reduce the impact of a temporary or even permanent occlusion (which is a blockage) of a single vessel.

 
The Pulmonary Circuit
 
The arteries of the pulmonary circuit carry deoxygenated blood. The pulmonary circuit includes the pulmonary trunk, the left and right pulmonary arteries, and the pulmonary veins, which empty into the left atrium. That’s really all I have on that one.
 
The Systemic Circuit

The ascending aorta gives rise to the coronary circulation. The aortic arch continues as the descending aorta. Three large arteries arise from the aortic arch to collectively supply the head, neck, shoulder, and upper limbs; the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery.

The brachiocephalic trunk gives rise to the right subclavian artery and the right common carotid artery. These arteries supply the right upper limb and portions of the right shoulder, neck, and head.

Each subclavial artery exits the thoracic cavity to become the axillary artery, which enters the arm to become the brachial artery. The brachial arteries and their branches supply blood to the upper limbs.

Each common carotid artery divides into an external carotid artery and internal carotid artery. The external carotids and their branches supply blood to structures of the neck and face. The internal carotids and their branches enter the skull to supply blood to the brain and eyes. The brain also receives blood from the vertebral arteries. The vertebral arteries and the internal carotids from the cerebral arterial circle (or circle of Willis), which ensures the blood supply to the brain.

The descending aorta superior to the diaphragm is called the thoracic aorta, and inferior to it is the abdominal aorta. The thoracic aorta and its branches supply blood to the thorax and the thoracic viscera. The abdominal aorta and its branches supply blood to the abdominal wall, abdominal viscera, pelvic structures, and lower limbs.

The three unpaired arteries are the celiac arteries, superior mesenteric artery, and the inferior mesenteric artery. The celiac trunk divides into the left gastric artery, common hepatic artery, and the splenic artery. Paired arteries include the suprarenal arteries, the renal arteries, the lumbar arteries, and the gonadal arteries. To actually see details on these blood vessels and their branches, you have to look at figures 22.10 to 22.18/22.20.
 
Arteries in the neck and limbs are deep beneath the skin; in contrast there are usually two sets of peripheral veins - one superficial and one deep. This dual venous drainage is important for controlling body temperature. Arteries of the pelvis and lower limbs include the right and left common iliac arteries which branch to form external and internal iliac arteries. The femoral and deep femoral arteries supply the lower limb (see fig 22.18). The arteries of the foot can be seen in figures 22.18 and 22.20.
 
The superior vena cava receives blood from the head, neck, chest, shoulders and upper limbs. The inferior vena cava collects most of the venous blood from organs and structures inferior to the diaphragm that are not drained by the hepatic portal vein.
 
Any blood vessel connecting two capillary beds is called a portal vessel and the network of blood vessels comprises the portal system.
 
Blood leaving capillaries supplied by the celiac superior and inferior mesenteric arteries flows into the hepatic portal system. Blood in the hepatic portal system is unique compared to that of the other system veins because portal blood contains high concentrations of nutrients. Levels of blood glucose and amino acids in the hepatic portal vein often exceed those found anywhere else in the circulatory system. These substances are collected from the digestive organs through the vessels of the portal system and are transported directly to the liver for processing.
 
Aging and the Cardiovascular System
 
Age-related changes in the blood can include:

1. Decreased hematocrit

2. Constriction or blockage of peripheral veins by a thrombus (stationary blood clot); the thrombus can become detaches, pass through the heart, and become wedged in a small artery, most often the lungs, causing a pulmonary embolism

 3. Pooling of blood of the veins in the lower legs because the valves are not working effectively
 
Age-related anatomical changes in the heart include:

1. A reduction in the maximum cardiac output

2. A reduction in the elasticity of the fibrous skeleton

3. Progressive arthrosclerosis that can restrict coronary circulation

4. Replacement of damaged cardiac muscle fibers with scar tissues
 
Age-related changes in blood vessels are often related to arteriosclerosis and include:

1. Inelastic walls of arteries become less tolerant of sudden increases in pressure which may lead to an aneurysm, causing a stroke, infarct, or massive blood loss, depending on the vessel involved

 2. Calcium salts which can deposit on weakened vascular walls increasing the risk of a stroke or infarct

3. Thrombi that form at athrosclerotic plaques

 
When I first started out writing this blog, I honestly had NO IDEA how I was going to do this chapter. Seriously, it was friggin crazy. So I basically used the study outline and just elaborated on it.  I hope it wasn’t too terrible to read, there really wasn’t much I could do for stories with this chapter.  So, good luck, and keep studying!

Happy Halloween!!! Here’s the chapter on blood! I think you guys deserve an “easier” chapter after you made it through the friggin endocrine system. So, let’s talk about blood!

 
Blood does everything. Well, not everything, but we’d be screwed if we didn’t have it. Here’s a list of just some of the functions (check out Table 20.1 to follow along).

1. Transport of dissolved gases, bringing oxygen from the lungs to the tissues and carrying carbon dioxide from the tissues to the lungs.
2. Distribution of nutrients absorbed from the digestive tract or released from storage in adipose tissue or the liver.
3. Transport of metabolic wastes from peripheral tissues to sites of excretion, especially in the kidneys.
4. Delivery of enzymes and hormones to specific target tissues.
5. Stabilization of the pH and electrolyte composition of interstitial fluids throughout the body.
6. Prevention of fluid losses through damaged vessels or at other injury sites. The clotting reaction seals the breaks in the vessel walls, preventing changes in blood volume that could seriously affect blood pressure and cardiovascular function.
7. Defense against toxins and pathogens.
8. Stabilization of body temperature by absorbing and redistributing heat.

Blood is a fluid connective tissue normally confined to the circulatory system. It consists of two components:

1. Plasma- which is the liquid matrix of the blood, contains dissolved proteins.
2. Formed elements are blood cells and cell fragments that are suspended in the plasma. Red blood cells (RBCs) transport oxygen and carbon dioxide. White blood cells (WBCs) are components of the immune system. Platelets are small, membrane-enclosed packets of cytoplasm that contain enzymes and other factors essential to blood clotting.
   

Whole blood is a mixture of plasma and formed elements. Its components may be separated, or fractionated, for clinical purposes. Whole blood is sticky, cohesive, and resistant to flow (sounds like my ex-boyfriend).  These characteristics determine the viscosity of a solution.

 Ok, how much whole blood do I have in me? How much does Dr. Mazurkie have? On average, I have 4-5 liters and Dr. Mazurkie has 5-6 liters of whole blood. Even though we have different amounts of blood in us, our blood temperature is about 100.4 F.

Hypovolemic means you have a low blood volume.

Normovolemic means you have a normal blood volume.

Hypervolemic means you have a high blood volume.

 
(This is all very thrilling)

 
Plasma

 Ok, whenever I hear the word plasma I think for some reason about Austin Powers. You know how Dr. Evil kept saying “magma”? That’s how I say plasma in my head. Try it, it’s really funny (or I just have too much time on my hands).

Anyway, plasma contributes approximately 55 percent of the volume of whole blood, and water accounts for 92 percent of the plasma values.

There are differences between plasma and interstitial fluid (don’t let anyone tell you differently). They are as follows:

1. Concentration of dissolved oxygen and carbon dioxide
2. Concentration of dissolved proteins.

The Plasma Proteins

 There are three major classes of plasma proteins

1. Albumins make up approximately 60 percent of the plasma proteins. They are major contributors to the osmotic pressure of the plasma. They are also important in the transport of fatty acids, steroid hormones, and other substances. They are the smallest of the major plasma proteins.
2. Globulins make up about 35 percent of the plasma protein populations. They include both immunoglobulins and transport globins.
1. Immunoglobulins (AKA antibodies) attack foreign proteins and pathogens
2. Transport globulins bind small ions, hormones, or compounds that either are insoluble or might be filtered out of the blood at the kidneys
3. Fibrinogen makes up about 4 percent of the plasma production. It participates in the clotting reaction. Under certain conditions, fibrinogen molecules interact, forming large, insoluble strand of fibrin. These fibers provide the basic framework of a blood clot.

Serum is blood plasma from which clotting agents have been removed.

Both albumins and globulins can attach to lipids, like triglycerides, fatty acids or cholesterol, that are not water-soluble. These protein-lipid combinations, called lipoproteins, readily dissolve in plasma, and this is how insoluble lipids are delivered to peripheral tissues. Pretty easy, right?

The liver synthesizes and releases more than 90 percent of the plasma proteins. Because the liver is the primary source of plasma proteins, liver disorders can alter the composition and functional properties of the blood.

Formed Elements

The two major cellular components of blood are red blood cells and white blood cells. Then, there are two major classes of white blood cells, granular (with granules) and agranular (without granules). Blood also contains non-cellular formed elements called platelets.

 
Red blood cells (AKA erythrocytes) account for slightly less than half of the total blood volume. The hematocrit value indicates the percentage of whole blood contributed by formed elements. The normal hematocrit in adult men averages about 46 and the average for women in 42. Because whole blood contains roughly 1000 RBCs for each WBC, the hematocrit closely approximates the volume of erythrocytes (RBCs). This is why hematocrit values are also known as the volume of packed red cells (VPRC) or just packed cell volume (PCV).

 
Erythrocytes transport both oxygen and carbon dioxide within the bloodstream (I’ll be saying that a lot). They are biconcave, which provides strength, flexibility and gives the RBC a disproportionately large surface area for a cell its size. The total surface area of the RBCs in the blood of a typical adult is 2000 times the total surface area of the body.

The biconcave shape enables the RBCs to form stacks, like dinner plates, and these stacks are called roleaux.

 Hemoglobin molecules account for more that 95 percent of erythrocyte’s proteins. It’s responsible for the cell’s ability to transport oxygen and carbon dioxide. It’s a red pigment, so the hemoglobin’s presence gives blood its characteristic red color.

 I’m giving you the definition of heme right from the glossary because I figure it’s easier to read it that way, as opposed to how the book explains it. Heme is defined as a porphyrin ring containing a central ion atom that can reversibly bind oxygen molecules. It’s a component of the hemoglobin molecule.

 As red blood cells circulate through capillaries in the lungs, oxygen enters and carbon dioxide leaves the plasma by diffusion. As plasma oxygen levels climb, oxygen diffuses into RBCs and binds to hemoglobin; as plasma carbon dioxide levels fall, hemoglobin releases carbon dioxide that diffuses into the plasma. And, as I said before, this explains that RBCs absorb oxygen and release carbon dioxide.

Blood Types

An individual’s blood type is determined by the presence or absence of specific components in erythrocyte cell membranes. A typical red blood cell membrane contains a number of surface antigens (or agglutinogens) exposed to the plasma. The surface antigens are glycoproteins or glycolipids whose characteristics are genetically determined. Three surface antigens of particular importance are A, B, and D (Rh).

 
Ok, now here are they blood types:

 
Type A blood has antigen A and anti-B antibodies

Type B blood has antigen B and anti-A antibodies

Type AB blood has surface antigens A and B and NO anti-A nor anti-B antibodies

Type O blood has neither A nor B surface antigens and has anti-A and anti-B antibodies

 
Type AB is the universal recipient and Type O is the universal donor.

 
The presence of the Rh antigen (which can also be called the Rh factor) is indicated by the terms Rh-postive (present) and Rh-negative (absent).

 
Antibodies and Cross-Reactions

 
Your plasma has antibodies (immunoglobulins) that will attack “foreign” surface antigens. These antibodies are known as agglutinins. The blood of a Type A, Type B, Type AB and Type O individual always contains antibodies that will attack foreign surfaces antigens. For example, if you have Type A blood, your plasma contains circulating anti-B antibodies that will attack Type B erythrocytes.

 
When an antibody meets its specific surface antigen, a cross-reaction occurs. Initially the red blood cells clump together, which is called agglutination, and they may also hemolyze, or rupture. Clumps and fragments of red blood cells under attack form drifting masses that can plug small vessels in the kidneys, lungs, heart, or brain, damaging or destroying the tissues deprived of circulation. So, for that reason, you have to make sure that the donor and recipient are compatible. That is very important, I cannot stress that enough.

 
White Blood Cells

 
White blood cells (or WBCs or leukocytes) are scattered throughout peripheral tissues. White blood cells help defend the body against invasion by pathogens and remove toxins, wastes, and abnormal or damaged cells. There are two major classes of white blood cells: granular leukocytes (or granulocytes) which have large granular inclusions and agranular leukocytes (or agranulocytes) which do not posses cytoplasmic granules visible with the light microscope.

 
Some randomish facts:

Leukopenia indicates inadequate numbers of WBCs.

Remember –penia means low and –osis means high with respect to WBCs

 A stained blood smear provides a differential count to the white blood cell population.

 Diapedisis- this is the process where in instances of injury or invasion of an area by a foreign organism, a leukocyte can migrate across the endothelial lining of a capillary by squeezing between adjacent endothelial cells.

 Chemotaxis is the attraction of phagocytic cells to the source of abnormal chemicals in tissue fluids.

Granular Leukocytes

Granular leukocytes are subdivided on the basis of their staining characteristics into neutrophils, eosinophils, and basophils.

Neutrophils make up 50 to 70 percent of the circulating white blood cells. They are called neutrophils because their cytoplasm is packed with pale, neutral-staining granules contain lysosomal enzymes and bactericidal compounds. A neutrophil has a very dense, contorted nucleus that may be condensed into a series of lobes like beads on a string, which gives the cells another name (polymorphonuclear leukocytes). Neutrophils are highly mobile and are usually the first of the WBCs to arrive at an injury site. They are very active phagocytes, specializing in attacking and digesting bacteria.

Eosinophils (AKA acidophils) are so named because their granules stain with eosin, an acidic red dye. Eosinophil numbers increase dramatically during an allergic reaction or a parasitic infection.

Basophils are named that because have numerous granules that stain with basic dyes, they stain a deep purple or blue. They’re relatively rare, accounting for less than 1 percent of the leukocyte population. Their granules contain histamine; its release exaggerates the inflammation response at the injury site by increasing capillary permeability. Basophils also release chemicals that stimulate mast cells and attract basophils and other WBCs to the area.

 
Agranular Leukocytes

 
Monocytes are the largest WBCs. Outside the bloodstream; monocytes are called free macrophages to distinguish them from the immobile fixed macrophages found in many connective tissues. Active macrophages secrete substances that lure fibroblasts into the region.

Lymphocytes are the primary cells of the lymphatic system, a network of special vessels and organs distinct from, but connect to, the cardiovascular system. Lymphocytes are responsible for specific immunity, the ability of the body to mount a counterattack against invading pathogens or foreign proteins on an individual basis.

Lymphocytes respond to threats in three ways:

T-cells enter peripheral tissues and attack foreign cells directly.

B-cells differentiate into plasma cells that secrete antibodies that attack foreign cells or proteins in distant portions of the body

NK cells, sometimes known as large granular lymphocytes, are responsible for immune surveillance, the destruction of abnormal tissue cells.

Platelets

 
Platelets are flattened, membrane-enclosed packets. The functions of platelets include the following:

1. Transport of chemicals important to the clotting process
2. Formation of a temporary patch in the walls of damaged blood vessels
3. Active contraction after clot formation has occurred

Megakaryocytes are enormous cells with large nuclei contained in normal red blood marrow. Megakaryocytes eventually become platelets (check out page 533). Thrombocytopenia is an abnormally low platelet count and indicates excessive platelet destruction of inadequate platelet production. Thrombocytosis is the presence of high platelet counts in the blood, which usually results from accelerated platelet formation in response to infection, inflammation, or cancer.

 
Hemostasis prevents the loss of blood through the walls of damaged vessels. In doing so, it both restricts blood loss and establishes a framework for tissue repairs.

 
Hemopoiesis is the process of blood cell formation.

Hemocytoblasts are stem cells, and produce all blood cells.

 
Look at Figure 20.8 and redraw that diagram. Seriously, it’ll be a big help.

 
Erythropoiesis refers specifically to the formation of erythrocytes. Blood cells are produced in areas of red marrow. Red marrow is found in portions of the vertebrae, sternum, ribs, skull, scapulae, pelvis and proximal limb bones. Under extreme conditions, the fatty yellow marrow found in other bones can be converted to red marrow. Erythropoiesis is regulated by erythropoiesis-stimulating hormone, or erythropoietin (EPO). Erythropoietin has two major effects:

1. It stimulates increased rates of cell division in erythroblasts and in the stem cells that produce erythroblasts
2. It speeds up the maturation of RBCs, primarily by accelerating the rate of hemoglobin synthesis.

 If I was only going to take one thing away from this chapter, it would be this:

Red blood cells transport both oxygen and carbon dioxide within the bloodstream.

White blood cells help defend the body against invasion by pathogens and remove toxins, wastes and abnormal or damaged cells

Platelets are important in the clotting response.

So that’s it! The next chapter is the heart, and is going to be a little longer, so it may take me two days to post it. So see you in two days, and Happy Halloween!!!!

I'm going to be doing this chapter a little differently. The following table 
(list) is in our book, but I think it's pretty handy to print the page, cut it 
out, and carry it around as a reference. It's the key to the pituitary 
hormones.
 
ACTH-Adrenocortiotropic hormone
TSH- Thyroid-stimulating hormone
GH-  Growth hormone
PRL- Prolactin
FSH- Follicle-stimulating hormone
LH-  Luteinizing hormone
MSH- Melanocyte-stimulating hormone
ADH- Antidiuretic hormone
 
Look at figure 19.1, it will tell you everything (disclaimer: everything as 
far as I know) about the endocrine system.
 
So the actual definition of hormones (according to the book anyway) are
chemicals in the bloodstream that alter the metabolic activities of many 
different tissues and organs simultaneously. The hormonal effects may not be 
apparent immediately, but when they appear, they often persist for days. This 
response pattern makes the endocrine system particularly effective in 
regulating ongoing processes such as growth and development.
 
 
THE ENDOCRINE SYSTEM
 
The endocrine system includes all of the endocrine cells and tissues of the 
body. Endocrine cells are glandular secretory cells that release hormones into 
the interstitial fluids.
 
Hormones are organized into four groups based on chemical structure.
 
Amino Acid Derivatives- These are relatively small molecules that are
structurally similar to amino acids.

Examples: 1. Derivatives of tyrosine, such as thyroid hormones released by the
thyroid gland and the catecholamines (E and NE) released by the adrenal 
medullae and 2. Derivatives of tryptophan, such as melatonin synthesized by the pineal 
gland.
 
Peptide hormones- chains of amino acids, the largest group, all pituitary
gland hormones are peptide hormones.
 
Steroid hormones- Derived from cholesterol, are released by the reproductive
organs and the adrenal glands.
 
Eicosanoids- small molecules with a five-carbon ring at one end. These
coordinate cellular activities and affect enzymatic processes (such as blood
clotting) that occur in extracellular fluids.
 
Hormones alter the metabolic activities of many different tissues and organs
simultaneously. Target cells are peripheral cells that respond to a hormone’s 
presence.
 
Endocrine activity is controlled by endocrine reflexes that are triggered by 
the following:

1.      Humoral stimuli (changes in the composition of the extracellular fluid)
2.      Hormonal stimuli (arrival or removal of a specific hormone)
3.      Neural stimuli (the arrival of neurotransmitters at neuroglandular junctions.
 
In most cases, endocrine reflexes are regulated by some form of negative 
feedback. Here’s a description of direct negative feedback control.
 
1.The endocrine cell responds to a disturbance in homeostasis by releasing its 
hormone into the circulatory system.

2.The released hormone stimulates a target cell (see definition above)

3.The target cell response restores homeostasis and eliminates the source of 
stimulation of the endocrine cell.
 
There are also complex negative feedback loops which are the most common 
regulatory mechanisms. This is where the secretion of one hormone, such as TSH 
from the anterior lobe of the pituitary gland, triggers the secretion of a 
second hormone, such as the thyroid hormones produced by the thyroid gland. 
The second hormone may have multiple effects, one of which ALWAYS includes the 
suppression of the release of the first hormone.
 
There is also hormone regulation through positive feedback, but is rare (at 
least that’s what I’m told). This is when the secretion of a hormone produces 
an effect that further stimulates hormone release. This one actually sounds a 
lot nicer to me, it’s too bad we don’t use it more often.
 
The Hypothalamus and Endocrine Regulation
 
So it’s the hypothalamus’ job to regulate the activities of the nervous and 
endocrine systems. It has coordinating centers that allows it to do this.
 
There are three different mechanisms: 
1. The hypothalamus secretes regulatory hormones (or regulatory factors) that 
control the activities of endocrine cells in the anterior lobe of the 
pituitary gland.

There are two classes of regulatory hormones: 
a. Releasing hormones (RH) stimulate production of one or more hormones at the 
anterior lobe of the pituitary gland.
b. Inhibiting hormones (IH) prevent the synthesis and secretion of specific 
pituitary hormones.
 
2. The hypothalamus acts as an endocrine organ, releasing the hormones ADH 
(Antidiuretic hormone) and oxytocin into the circulation at the posterior lobe 
of the pituitary gland.
 
3. The hypothalamus contains autonomic centers that exert direct neural control 
over the endocrine cells of the adrenal medullae. When the sympathetic 
division is activated, the adrenal medullae release hormones into the 
bloodstream.
 
THE PITUITARY GLAND
 
The pituitary gland (or hypophysis) is like a small grape. I’m not kidding, 
that’s what the book says. It’s the most compact chemical factory in the body 
(OOOOOOHH!) It lies inferior to the hypothalamus within the sella turcica 
(quick, where is the sella turcica?)
 
The infundibulum extends from the hypothalamus inferiorly to the posterior and 
superior surfaces of the pituitary gland. The diaphragma sellae encircles the 
stalk of the infundibulum and holds the pituitary gland in position within the 
sella turcica.
 
The pituitary gland has both posterior and anterior lobes. There are nine 
important peptide hormones released by the pituitary gland, two by the 
posterior lobe and seven by the pars distalis and pars intermedia of the 
anterior lobe (look at Table 19.1 and Figure 19.4 now).
 
Let’s look at closer at the posterior lobe of the pituitary gland:
 
The pituitary gland has three names. “Pituitary Gland” “neurohypophysis” and
“pars nervosa”. It’s a multiple personality, it doesn’t know what it wants to 
be called.
 
It contains the axons and axon terminals of about 50K hypothalamic neurons 
whose cell bodies are in either supraoptic or paraventricular nuclei. The 
axons extend from these nuclei through the infundibulum and end in synaptic 
terminals in the posterior lobe.
 
The hypothalamic neurons manufacture ADH and oxytocin, which are called 
neurosecretions because they are produced and released by neurons. Once 
released they enter local capillaries supplied by the inferior hypophyseal 
artery, and then will be transported into the general circulation.
 
ADH: This is the antidiuretic hormone (or vasopressin), and it’s primary 
function is to decrease the amount of water lost at the kidneys. It also 
causes the constriction of peripheral blood vessels, which helps elevate blood 
pressure.
 
Oxytocin: These functions are best known in women (because we are awesome). 
Oxytocin stimulates the contractions of smooth muscle cells in the uterus and 
contractile cells surrounding the secretory cells of the mammary glands. In 
the guys, oxytocin causes smooth muscle contractions in the prostate gland.
 
Onto the anterior lobe!
 
The anterior lobe (or adenohypophysis) can be subdivided into three regions:  
1. Pars distalis which is large and represents the major portion of the 
pituitary gland.
2. Pars intermedia which is slender and forms a narrow band adjacent to the 
neurohypophysis
3. Pars turberalis, which is an extension and wraps around the adjacent 
portion of the infundibulum.
 
The entire adenohypophysis is RICHLY VASCULARIZED (I’m putting that in bold 
because Dr. Mazurkie likes to ask questions about things being vascularized, 
and if that was on the exam, we would now get it right).
 
Ok, I’ve read the section on the Hypophyseal Portal System, and to be honest, 
I don’t want to write about it. Not because I’m lazy, but because I’m afraid 
I’m going to explain it wrong and screw it up for everyone. So read page 508. I 
have more hormones to discuss.
 
We’ve already talked about the hormones of the posterior lobe, now it’s time 
for the anterior lobe. Remember how earlier I said there were seven to 
discuss? Here they are.
 
1. Thyroid-stimulating hormone (TSH) targets the thyroid gland and triggers 
the release of thyroid hormones. TSH is secreted by cells called thyrotropes.

2. Adrenocorticotropic hormone (ACTH) stimulates the release of steroid 
hormones by the adrenal gland. It specifically targets cells producing 
hormones called glucocorticiods (GC) that affect glucose metabolism. The cells 
that secret ACTH are called corticotropes.

3. Follicle-stimulating hormones (FSH) promotes the development of oocytes 
(female gametes) within the ovaries of mature women. FSH also stimulates the 
secretion of estrogens by follicle cells (estradiol is the most important 
estrogen). For men, FSH secretion supports sperm production in the testes.

4. Luteinizing hormone (LH) induces ovulation in women and promotes the 
ovarian secretion of progestins, which are steroid hormones that prepare the 
body for possible pregnancy. Progesterone is the most important progestin. In 
men, LH stimulates the production of male sex hormones called androgens by the 
interstitial cells of the testes. Testosterone is the most important androgen.
 
(FSH and LH are called gonadotropins because they regulate the activities of 
male and female sex organs. They are produced by cells called gonadotropes.)
 
5. Prolactin (PRL) stimulates the development of the mammary glands and the 
production of milk. It's function in men is poorly understood. PRL is secreted 
by cells called lactotropes.

6. Growth hormone (GH) (AKA human growth hormone or somatotropin) stimulates 
cell growth and replication by accelerating the rate of protein synthesis. GH 
is secreted by cells called somatropes. GH has a particularly strong effect on 
skeletal and muscular development. 

7. Melanocyte-stimulating hormone (MSH) is the only hormone released by the 
pars intermedia (that would be another good question on the exam). MSH 
stimulates the melanocytes of the skin, increasing their rates of melanin 
production and distribution.
 
Ok, one good thing about this section, the names pretty much tell you what 
they do. I know I said this before, but Figure 19.4 really is a good diagram 
for this section.
 
THE THYROID GLAND
 
The thyroid gland curves across the anterior surface of the trachea (which is 
our windpipe) just inferior to the thyroid cartilage that dominates the 
anterior surface of the larynx.
 
The blood supply to the gland is from two sources:
1. A superior thyroid artery which is a branch from the external carotid 
artery.
2. An inferior thyroid artery, a branch of the thyrocervical trunk.
 
Venous drainage of the gland is through the superior and middle thyroid veins 
which end in the internal jugular veins and the inferior thyroid veins, which 
deliver blood to the brachiocephalic veins.
 
The thyroid gland has a butterfly-like appearance and consists of two main 
lobes. The two lobes are united by a slender connection called the isthmus. 
The thyroid gland is anchored to the tracheal rings by a thin capsule that is 
continuous with connective tissue partitions that segment the glandular tissue 
and surround the thyroid follicles.
 
Thyroid follicles manufacture, store, and secrete thyroid hormones. They 
resemble miniature tennis balls. The follicle cells surround a follicle cavity 
which contains colloid. Colloid is a viscous fluid containing large quantities 
of suspended proteins. Follicle cells have abundant mitochondria and an 
extensive rough endoplasmic reticulum. Follicular cells synthesize a globular 
protein called thyroglobulin and secrete it into the colloid of the thyroid 
follicle. Read page 509 for explanations of ionization.
 
The major factor controlling the rate of thyroid hormone release is the 
concentration of TSH in the circulating blood. Under the influence of 
thyrotropin-releasing hormone (TRH) from the hypothalamus, the anterior lobe 
of the pituitary gland releases TSH.  Again, I’m not touching on the formation 
of T3 and T4 because I don’t want to screw it up for anyone. The rest of the 
stuff I know I’m explaining correctly, but when it comes to that kind of 
chemistry stuff I don’t want to confuse anyone.
 
C-cells are a type of endocrine cells that lie among the cuboidal follicle 
cells of the thyroid. C-cells can occur singly or in small groups. C-cells 
produce calcitonin, which assists in the regulation of calcium ion 
concentrations in body fluids, especially under physiological stresses such as 
starvation or pregnancy.
 
Calcitonin lowers calcium ion concentrations by: 
1. inhibiting osteoclasts
2. stimulating calcium ion excretion at the kidneys.
 
The actions of calcitonin are opposed by those of parathyroid hormone, 
produced by parathyroid glands.
 
 
Make sure you review Figure 19.7, which is the regulation of thyroid 
secretion.
 
 
The Parathyroid Glands
 
There are typically four pea-sized reddish brown parathyroid glands located on 
the posterior surfaces of the thyroid gland.
 
There are two types of cells in the parathyroid glands:
1. Principal cells (or chief cells) are glandular cells that produce the 
hormone parathyroid hormone (PTH). 
2. The other major cell types (oxyphil and transitional cells) are probably 
immature or inactive principal cells).
 
PTH is important because it increases calcium ion concentrations in body 
fluids and increases bone mass (see Table 19.2 for an awesome chart).
 
The Thymus
 
The thymus is embedded in a mass of connective tissue inside the thoracic 
cavity, usually  just posterior to the sternum. The thymus produces several 
hormones important to the development and maintenance of normal immunological 
defenses.
 
Thymosin was the name originally given to a thymic extract that promoted the 
development and maturation of lymphocytes and thus increased the effectiveness 
of the immune system. Well, it turns out that "thymosin" is actually a blend 
of several different, complementary hormones.
 
The Adrenal Glands
 
Adrenal glands are yellow, pyramid-shaped glands firmly attached to the 
superior border of each kidney by a dense, fibrous capsule. Like the other 
endrocrine glands, the adrenal glands are highly vascularized. Branches of the 
renal artery, the inferior phrenic artery, and a direct branch from the aorta 
(the middle suprarenal artery) supply blood to each adrenal gland. The 
suprarenal veins carry blood away from the adrenal glands.
 
Structurally and functionally, the adrenal gland can be divided into two 
regions, each secreting different hormone types, but both aiding in managing 
stress: a superficial adrenal cortex and an inner adrenal medulla.
 
The adrenal cortex is yellowish in color because of the presence of stored 
lipids, especially cholesterol and various fatty acids. The adrenal cortex 
produces more than two dozen different steroid hormones, collectively called 
adrenocortical steroids (or just cortical steroids). These hormones are wicked 
vital, if the adrenal glands are destroyed or removed, corticosteroids must be 
administered or the person will die.
 
Deep to the adrenal capsule are three distinct regions (or zones) in the 
adrenal cortex. There's an outer zona glomerulosa, a middle zona fasciculata 
and an inner zona reticularis.
 
The zona glomerulosa is the outermost cortical region, and accounts for about 
15% of the cortical volume. (Side note: a glomerulus is a liittle ball or 
knot, and here the endocrine cells form densly packed clusters). The zona 
glomerulosa produces mineralocorticoids (MC), steroid hormones that affect the 
electrolyte composition of bodily fluids.
 
Aldosterone is the principal mineralocorticoid and targets kidney cells that 
regulate the ionic composition of the urine. It causes the retention of sodium 
ions and water, thereby reducing fluid losses in the urine. It also reduces 
sodium and water losses at the sweat glands, salivary glands, and along the 
digestive tract. It also promotes the loss of potassium ions in the urine and 
other sites as well.
 
The zona fasciculata  begins at the inner border of the zona glomerulosa and 
extends toward the medulla. It makes up about 78% of the cortical volume. The 
cells are larger and contain more lipids than those of the zona glomerulosa, 
and the lipid droplets give the cytoplasm a pale, foamy appearance.
 
Ok, I think this is one of the prettiest sentences in the entire book:
 
"The cells of the zona fasciculata  form cords that radiate like a sunburst 
from the zona reticularis."  (You can tell the authors were really trying 
here.)
 
Steriod production in the zona fasciculata  is stimulated by ACTH from the 
anterior lobe of the pituitary gland. This zone produces steroid hormones 
collectively known as glucocorticoids (GC) because of their effects on glucose 
metabolism. Cortisol and corticosterone are the most important glucocorticoids 
secreted by the adrenal cortex; the liver converts some of the circulating 
cortisol to cortisone. These hormones speed up the rates of glucose synthesis 
and glycogen formation, especially within the liver.
 
The Zona Reticularis
 
The zona reticularis forms a narrow band between the zona fasciculata  and the 
outer border of the adrenal medulla. The cells of the zona reticualris are much 
smaller than those of the medulla. The zona reticularis only makes up about 
7% of the total cell volume of the adrenal cortex. The zona reticularis 
normally secrets small amounts of sex hormones called androgens (remember 
those?) Adrenal androgens stimulate the development of pubic hair in boys and 
girls before puberty. The androgens aren't really that important in adult ment
(because their testes produce androgens in relatively large amounts) in adult 
women adrenal androgens promote muscle mass, stimulate blood cell formation, 
and support the libido.
 
The Adrenal Medulla
 
The adrenal medulla has a reddish-brown coloration due partially to the many 
blood vessels in this area. Pheochromocytes (or chromaffin cells) are large, 
rounded cells of the medulla that resemble the neurons in the sympathetic 
ganglia.
 
The adrenal medulla contains two populations of endocrine cells, one secreting 
epinepherine (adrenaline) and one secreting norepinepherine (noradrenaline). 
The adrenal medulla secretes roughly three times as much E as NE. Their 
secretion triggers cellular energy utilization and the mobilization of 
energy reserves. The metabolic changes that follow catecholamine release are 
at their peak 30 seconds after adrenal stimulation, and they linger for 
several minutes thereafter. This is why the effects produced by stimulation of 
the adrenal medulla outlast the other signs of sympathetic activation.
 
Table 19.3 is an excellent table that summarizes all the stuff I just talked 
about.
 
The Endocrine Function of the Kidneys and the Heart
 
The kidneys and the heart produce several hormones, and most of the are 
involved with the regulation of blood pressure and blood volume. The kidneys 
produce renin an enzyme (often called a hormone) and two hormones: 
erythropoietin (a peptide) and calcitroil (a steroid).
 
Once in circulation, renin converts circulating angiotensinogen, an inactive 
prrotein produced by the liver to angiotensin I. In capillaries of the lungs, 
this compound is converted to angiotensin II, the hormone that stimulates the 
secretion of aldosterone by the adrenal cortex. Erythropoietin (IPO) 
stimulates red blood cell production by the bone marrow. This hormone is 
released when either blood pressure or oxygen levels in the kidneys decline. 
EPO stimulates red blood cell production and maturation, thus increasing the 
blood volume and its oxygen-carrying capacity.
 
Calcitriol is a steroid hormone secreted by the kidney in response to the 
presence of PTH (parathyroid hormone). Check out the relationship between 
calcitroil and vitimin D3 on page 514. The best known function of calcitriol 
is stimulation of calcium and phosphate ion absorption along the digestive 
tract. PTH stimulates the release of calcitoril, and in this way, PTH has an 
indirect effect on intestinal calcium absorption.
 
Cardiac muscle cells in the heart produce atrial natriuretic peptide (ANP) and 
brain natriuretic peptide (BNP)  in response to increased blood pressure or 
blood volume. ANP and BNP suppress the release of ADH and aldosterone and 
stimulate water and sodium ion loss at the kidneys. These effects gradually 
reduce both blood pressure and blood volume.
 
The Pancreas and Other Endocrine Tissues of the Digestive Tract
 
The pancreas is a mixed gland with both exocrine and endocrine activities. 
It's a nodular organ occupying space between the stomach and the small 
intestine. The exocrine pancreas, which makes up about 99% of the pancreatic 
volume, produces large quantities of a digestive enzyme-rich fluid that enters 
the digestive tract through a prominent secretory duct.
 
The endocrine pancreas consists of small groups of cells scattered throughout 
the gland, each group surrounded by exocrine cells. These groups, called 
either pancreatic islets or the islets of Langerhans, account for only about 
1% of the pancreatic cell population.
 
Like other endocrine tissue, the islets are surrounded by an extensive 
fenestrated capillary network that carries its hormones into the circulation. 
Two major arteries supply blood to teh pancreas, the pancreaticoduodenal 
arteries and pancreatic arteries. Venous blood returns to the hepatic portal 
vein. The islets are also innervated by the autonomic nervous system, through 
branches from the celiac plexus.
 
Each islet contains four major cell types:
 
1. Alpha cells produce the hormone glucagon which raises blood glucose levels
by increasing the rates of glycogen breakdown and glucose release by the 
liver.
 
2. Beta cells produce the hormone insulin, which lowers blood glucose by 
increasing the rate of glucose uptake and utilization by most body cells.
 
3. Delta cells produce the hormone somatostatin which inhibits the production 
and secretion of glucagon and insulin and slows the rates of food absorption 
and enzyme secretion along the digestive tract.
 
4. F-cells produce the horomone pancreatic polypeptide (PP). It inhibits 
gallbladder contractions and regulates the production of some pancreatic 
enzymes; it may help control the rate of nutrient absorption by the digestive 
tract.
 
Look at Table 19.4 for a summary of all that.
 
Endocrine Tissues of the Reproductive System
 
Testes
 
In a guy, the interstitial cells of the testes produce androgens (how many 
times have I said that so far in this blog?) The most important androgen is 
testosterone, which promotes the production of functional sperm, maintains 
the secretory glands of the reproductive tract, influences secondary sexual 
characteristics, and stimulates muscle growth. Sustentacular cells, which are 
directly associated with the formation of functional sperm, secrete an 
additional hormone called inhibin. These two hormones work together to maintain 
sperm production at normal levels.
 
Ovaries
 
In the ovaries, oocytes begin their maturation into female gametes (sex cells) 
within specialized structures called follicles. The maturation process starts 
in response by FSH. Follicle cells surrounding the oocytes produce estrogens, 
especially estradiol. These steroid hormones support the maturation of the 
oocytes and stimulate the growth of the uterine lining. Under FSH stimulation, 
active follicles secret inhibin, which suppresses FSH release comparable to the 
one I described for the guys.
 
After ovulation has occurred, the remaining follicular cells reorganize into a 
corpus luteum that releases a mixture of estrogens and progestins, especially 
progesterone. Progesterone accelerates the movement of the oocyte along the 
uterine tube and prepares the uterus for the arrival of the developing embryo.
 
Ok, now look at Table 19.5. For some reason when I was taking notes in class I 
starred Relaxin, so I think we have to know it.
 
The Pineal Gland (hang in there, we're almost done, I promise)
 
The pineal gland (or epiphysis) is small, red, and pine cone-shaped. It's part 
of the epithalamus, and contains neurons, glial cells and special secretory 
cells called pinealocytes. Pinealocytes synthesize the hormone melatonin (which 
is derived from molecules of the neurotransmitter serotonin). Melatonin slows 
the maturation of sperm, oocytes, and reproductive organs by inhibiting the 
production of a hypothalamic relasing factor that stimulates FSH and LH 
secretion. Melatonin production rises at night and declines during the day. 
This cycle is important in regulating circadian rhythms (our natural 
awake-sleep cycles). This hormone is also a powerful antioxidant that may  
help protect CNS tissues from toxins generated by active neurons and glial 
cells.
 
A very quick word on hormones and aging:
 
The most dramatic exceptions in functional changes with age are:
 
1. The changes in reproduction hormone levels at puberty
2. The decline in the concentration of reproductive hormones at menopause in 
women.
 
I don't know about you, but I'm finding the chapters are a little easier to 
understand (I may be kicking myself for saying that after the exam). It seems 
to me that when something seems easy (like ADH is really antidiuretic hormone) 
it actually is. Thanks for sticking with me for yet another exciting chapter 
in Anatomy. For those of you who are wondering, if you take this blog, copy and paste it into 
Microsoft Word, it ends up being 14 pages (in case anyone wanted to print it out).
 
One week until the exam...

The ANS regulates body temperature and coordinates cardiovascular, respiratory, digestive, excretory and reproductive functions. 
Because it does all this stuff, it adjusts internal water, electrolyte, nutrient, and dissolved-gas concentrations in body fluids outside our conscious awareness.

A Comparison of the SNS and ANS
 
The ANS (like the SNS) has afferent and efferent neurons (I knew those would
come back to haunt us!)
 
The afferent sensory information of the ANS is processed in the central
nervous system, and then efferent impulses are sent to effector organs.
 
BUT...in the ANS the afferent pathways originate in visceral receptors, and
the efferent pathways connect to visceral effector organs.
 
Stuff about axons:
 
In the ANS, the axon of a visceral motor neuron within the CNS innervates a
second neuron located in a peripheral ganglion. This second neuron controls
the peripheral effector. Visceral motor neurons in the CNS (known as
preganglionic neurons) send their axons (called preganglionic fibers) to
synapse on ganglionic neurons, whose cell bodies are located outside the CNS,
in autonomic ganglia.
 
Axons that leave the autonomic ganglia are relatively small and unmyelinated.
These axons are called postganglionic fibers because they carry impulses away
from ganglion. Postganglionic fibers innervate the peripheral tissues and
organs, such as cardiac and smooth muscle, adipose tissue, and glands.
 
SUBDIVISIONS OF THE ANS
 
The ANS has two MAJOR subdivisions, the sympathetic division and the
parasympathetic division. Most often the two divisions have opposing effects,
if the sympathetic division causes excitation, the parasympathetic division
causes inhibition. But, this isn't always the case (find out why on 446).
 
In general, the parasympathetic division predominates under resting
conditions, and the sympathetic division "kicks in" during times of exertion,
stress, or emergency.
 
The sympathetic division is also known as the thoracolumbar division of the
ANS. Why? I'm glad you asked. Well, it's because the preganglionic fibers from
both the thoracic and upper lumbar spinal segments synapse in ganglia near the
spinal cord. So the name (thoracolumbar) really says it all.
 
The parasympathetic division is also known as the craniosacral division. Ok,
before I tell you why, which divisions do you think this is named after?
Preganglionic fibers originating in either the brain stem (cranial nerves
III, VII, IX and X) or the sacral spinal cord are part of the parasympathetic
division. So, again, the name says it all.
 
I am going to use my friends John and Christine to demonstrate the functions
of the parasympathetic and sympathetic divisions from here on out. It's just
easier using people I know (and I know are reading this, hi guys!) I'm going
to go a little out of order from the book, and give you the functions of the
divisions first, because for me, to know what they do first and then learn all
the anatomy stuff just makes more sense. If it doesn't work for you, print
this out, and cut and paste it so it goes in order of the book.
 
The story of John vs. the squirrels.
 
John was walking from Anatomy class one day, and for some reason,
he's attacked by one of the thousands of squirrels on campus (you have to
imagine that he's afraid of squirrels or this doesn't work. He's not, but
pretend he is. I would use Dr. Mazurkie's analogy about a lion, but we're all
too busy to be going on safari right now, we have more of a chance to be
attacked by squirrels).
 
Anyway, he's walking out of BISC and past the lovely construction, and in the
distance he sees some movement. It's a grouping of squirrels, and they look
pissed. Sympathetic activation (which I'll give the actual definition of
later) is now going to occur. His pupils are going to dilate, this way, he can
see the group of menacing squirrels a lot better. He is going to become
incredibly alert (through stimulation of the reticular activating system),
which is going to make him feel "on edge." He's going to have a strange
feeling of energy and euphoria (he's about to kick some ass), and with this
feeling, a disregard for danger and a temporary insensitivity to painful
stimuli. His blood pressure is going to rise, and so are his heart rate,
breathing rate and depth of respiration (this is due to increased activity in
the cardiovascular and respiratory centers of the pons and medulla oblongata).
There's also going to be a general elevation in muscle tone through
stimulation of the extrapyramidal system, so that John LOOKS like he's about
to kick ass (he may even shiver). Finally, the body will start to mobilize his
energy reserves, through the accelerated breakdown of glycogen in muscle and
liver cells and the release of lipids by adipose tissues.
 
There are more things that are going to be going on in his body at that
moment, but check out page 449 and 452 for the entire list. What you have to
learn is that this (the sympathetic division) is know as "fight or flight".
Basically are you going to kick some ass or run away? For the record, John won
the fight.
 
 
Let's look a the functions of the parasympathetic division now.

The story of Christine at the library.
 
Let's picture Christine sitting in the library after dinner. She's generally
relaxed, just hanging out and reading her Anatomy text. She is not in any
immediate danger (John took care of the squirrels, Christine is set) and she's
just studying. So, instead of her pupils being dilated like John's were, hers
are constricted, to restrict the amount of light entering the eyes. This
allows her to focus on her Anatomy book right in front of her. Because she's
not in any danger, her body can do other important things, like digest her
dinner. There will be increased smooth muscle activity along the digestive
tract. There will also be secretion by digestive glands, including salivary
glands, gastric glands, duodenal and other intestinal glands, the pancreas and
the liver. There will also be secretion of hormones that promote nutrient
absorption by peripheral cells. There will also be a reduction in heart rate
and force of contraction, because she's so relaxed.
 
There are more functions, but they don't really relate to her story. They are:
 
Contraction of the urinary bladder during urination
Stimulation and coordination of defecation
Constriction of the respiratory passageways
Sexual arousal and stimulation of sexual glands in both sexes.
 
 
The parasympathetic division is also known as the "rest and repose" or "rest
and digest" division.
 
Remember:
 
sympathetic division = fight or flight
parasympathetic division = rest and repose
 
 
There is actually a third division, called the enteric nervous system (or
ENS). This mainly deals with digestion. I'm not going to go into this, because
we learn more about it in Chapter 25.
 
 
Ok, back to following the text.
 
Innervation Patterns of the ANS
 
The sympathetic and parasympathetic divisions of the ANS affect their target
organs through the controlled release of neurotransmitters by postganglionic
fibers. Target organ activity may be either stimulated or inhibited, depending
on the response of the membrane receptor to the presence of the
neurotransmitter.
 
Three general statements describe ANS neurotransmitters and their effects:
 
1. ALL preganglionic autonomic fibers release acetylcholine (ACh) at their
synaptic terminals. The effects are ALWAYS stimulatory.
 
2. Postganglionic parasympathetic fibers also release ACh, but the effects may
be either stimulatory or inhibitory, depending on the nature of the receptor.
 
3. Most postganglionic sympathetic terminals release the neurotransmitter
norepinephrine (NE). The effects are usually stimulatory.
 

The Sympathetic Division (John's Division)
 
The sympathetic division consists of the following:
 
1. Preganglionic neurons located between T1 and L2 of the spinal cord.

The cell bodies of these neurons occupy the lateral gray horns between T1 and L2,
and their axons enter the ventral roots of those segments.
 
2. Ganglionic neurons in ganglia near the vertebral column.

There are two types of ganglia in the sympathetic division:

a. Sympathetic chain ganglia (or paravertebral, or lateral ganglia) lie
lateral to the vertebral column on each side. Neurons in these ganglia control
effectors in the body wall, head and neck, and limbs, and inside the thoracic
cavity.

b. Collateral ganglia (also known as prevertebral ganglia) lie anterior to the
vertebral column. Neurons in these ganglia innervate effectors in the
abdominopelvic cavity.
 
3. Specialized neurons in the interior of the adrenal glad.

The core of each adrenal gland, an area known as the adrenal medulla, is a
modified sympathetic ganglion. The ganglionic neurons here have very short
axons, and when stimulated, they release neurotransmitters into the
bloodstream for distribution throughout the body as hormones.
 
Let's look at the Sympathetic Chain Ganglia a little more closely (Figure 17.1a
in the book is actually a good diagram for this):
 
The ventral roots of spinal segments T1 to L2 contain sympathetic
preganglionic fibers. Each ventral root joins the corresponding dorsal root,
which carries afferent sensory fibers, to form a spinal nerve that passes
through an intervertebral foramen. As it clears the foramen, a white ramus (or
white ramus communicans) branches from the spinal nerve. The white ramus
carries myelinated preganglionic fibers into a nearby sympathetic chain
ganglion.
 
Fibers entering a sympathetic chain ganglion may have one of three
destinations:
 
1. They may synapse within the sympathetic chain ganglion at the level of
entry
2. They may ascend or descend within the sympathetic chain and synapse with a
ganglion at a different level.
3. They may pass through the sympathetic chain without synapsing and proceed to
one of the collateral ganglia or the adrenal medullae.
 
Ok, know this ratio: 1:32. It comes up a lot in this chapter. One
preganglionic fiber can synapse onto as many as 32 ganglionic neurons. This is
extensive divergence.
 
Preganglionic fibers projecting between the sympathetic chain ganglia
interconnect them, making the chain resemble a string of beads. Each ganglion
in the sympathetic chain innervates a particular body segment or group of
segments.
 
If a preganglionic fiber carries motor commands that target structures in the
body wall or the thoracic cavity, it will synapse in one or more of the
sympathetic chain ganglia. Unmyelinated postganglionic fibers then leave the
sympathetic chain and proceed to their peripheral targets within spinal nerves
and sympathetic nerves. Postganglionic fibers that innervate structures in the
body wall, such as the sweat gland of the skin or the smooth muscles in
superficial blood vessels, enter the gray ramus (gray ramus communicans) and
return to the spinal nerve for subsequent distribution.
 
Spinal nerves do not provide motor innervation to structures in the ventral
body cavities. Postganglionic fibers innervating visceral organs in the
thoracic cavity, such as the heart and lungs, proceed directly to their
peripheral targets as sympathetic nerves. These nerves are usually named after
their primary targets, as in the case of the cardiac nerves and the esophageal
nerves.
 
 
I want to apologize for those past few paragraphs. There was absolutely no way
I could make any of that fun, and I have a feeling all of that is going to be
on the test in one way or another.

 
Anatomy of the Sympathetic Chain
 
Each sympathetic chain has 3 cervical, 11-12 thoracic, 2-5 lumbar, and 4-5
sacral sympathetic ganglia and 1 coccygeal sympathetic ganglion. Again,
preganglionic sympathetic neurons are limited to segment T1-L2 of the spinal
cord, and the spinal nerves of these segments have both white rami
(preganglionic fibers) and gray rami (postganglionic fibers) The neurons in
the cervical, inferior lumbar, and sacral sympathetic chain ganglia are
innervated by preganglionic fibers extending along the axis of the chain.
 
Ok, they say this a lot, so I'm going to make it it's own section:
 
Every spinal nerve has a gray ramus that carries sympathetic postganglionic
fibers.
 
 
In summary:
 
1. Only the thoracic and superior lumbar ganglia receive preganglionic fibers
from white rami.

2. The cervical, inferior lumbar, and sacral chain ganglia receive
preganglionic innervation from the thoracic and superior lumbar segments
through preganglionic fibers that ascend or descend along the sympathetic
chain.

3. Every spinal nerve receives a gray ramus from a ganglion of the sympathetic
chain.

Collateral Ganglia
 
Preganglionic fibers that regulate the activities of the abdominopelvic
viscera originate at preganglionic neurons in the inferior thoracic and
superior lumbar segments of the spinal cord. These fibers pass through the
sympathetic chain without synapsing and converge to form the greater, lesser
and lumbar splanchnic nerves in the dorsal wall of the abdominal cavity.
Splanichnic nerves from both sides of the body converge on collateral ganglia.
 
Postganglionic fibers that originate within the collateral ganglia extend
throughout the abdominopelvic cavity, innervating visceral tissues and organs.
Now would be a good time to look at figure 17.3b.
 
The general pattern is
1. A reduction in blood flow, energy use, and activity by visceral organs that
are not important to short term survival (such as the digestive tract)
2. The release of stored energy reserves.
 
 
ANATOMY OF COLLATERAL GANGLIA
 
The splanchnic nerves (remember greater, lesser, lumbar, and sacral) innervate
three collateral ganglia. Preganglionic fibers from the seven inferior
thoracic segments end at the celiac ganglion and the superior mesenteric
ganglion. These ganglia are embedded in an extensive, weblike network of nerve
fibers called autonomic plexus. Preganglionic fibers from the lumbar segments
form splanchnic nerves that end at the inferior mesenteric ganglion. Let's
look at those three kinds of ganglia.
 
Celiac Ganglion:
Postganglionic fibers from the celiac ganglion innervate the stomach,
duodenum, liver, gallbladder, pancreas and spleen.
 
Superior Mesenteric Ganglion:
Postganglionic fibers leaving the superior mesenteric ganglion innervate the
small intestine and the initial segments of the large intestine.
 
Inferior Mesenteric Ganglion:
Postganglionic fibers from this ganglion provide sympathetic innervation to
the terminal portions of the large intestine, the kidney and bladder, and the
sex organs.
 
 
Adrenal Medullae
 
Some preganglionic fibers originating between T5 and T8 pass through the
sympathetic chain and the celiac ganglion without synapsing and proceed to the
core of the adrenal medullae. There, these preganglionic fibers synapse on
modified neurons that perform an endocrine function. These neurons have very
short axons. When these are stimulated, they release epinephrine (E) and
norepinephrine (NE) into an extensive network of capillaries. The
neurotransmitters then function as hormones, exerting their effects in other
regions of the body. Epinephrine, also called adrenaline, accounts for 75-80%
of the output, the rest is norepinephrine. The circulating blood then
distributes these hormones throughout the body.
 
Ok, here's the sympathetic activation I was talking about earlier.
 
The sympathetic division can change tissue and organ activities both by
releasing NE at peripheral synapse and by distributing E and NE throughout
the body in the bloodstream. The motor fibers that target specific effectors,
such as smooth muscle fibers in blood vessels of the skin, can be activated
in reflexes that do not involve other peripheral effectors. IN A CRISIS, THE
ENTIRE DIVISION RESPONDS (this is called sympathetic activation). It affects
peripheral tissues and alters CNS activity. Sympathetic activation is
controlled by sympathetic centers in the hypothalamus. You can read page 452
to see what happens when sympathetic activation occurs, but it's pretty much
what happens when John fought the squirrels (minus the pupil dilation).
 
 
We are almost done with the sympathetic division, I promise.
 
 
Sympathetic Activation and Neurotransmitter Release
 
When they are active, sympathetic preganglionic fibers release ACh at their
synapses with ganglionic neurons. These are CHOLINERGIC synapes. The ACh
released ALWAYS stimulates the ganglionic neurons. The stimulation of
ganglionic neurons usually leads to the release of NE at neuroeffector
junctions, and these sympathetic terminals are called adrenergic.
 
Let's look at varicosities
 
Telodendria from an extensive branching network, rather than ending at a
single synaptic knob. Each branch resembles a string of pop-beads, and each
pop-bead (or varicosity) is packed with mitochondria and neurotransmitter
vesicles. These varicosities pass along or near the surfaces of many effector
cells.
 
Membrane Receptors and Sympathetic Function
 
There are two classes of sympathetic receptors sensitive to E and NE; alpha
receptors and beta receptors.
 
Stimulation of alpha receptors on the surfaces of smooth muscles cells causes
constriction of peripheral blood vessels and the closure of sphincters along
the digestive tract.
 
Beta receptors are found in many organs including skeletal muscles, the smooth
muscle surrounding respiratory airways, the heart and the liver. Stimulation
of these beta receptors trigger changes in the metabolic activity of the
target cells.
 
 
A Summary of the Sympathetic Division
 
1. The sympathetic division of the ANS includes two sympathetic chains
resembling a string of beads, one on each side of the vertebral column; three
collateral ganglia anterior to the spinal column; and two adrenal medullae.
 
2. Preganglionic fibers are short because the ganglia are close to the spinal
cord. The postganglionic fibers are relatively long and extend a considerable
distance before reaching their target organs. (In the case of the adrenal
medullae, very short axons from modified ganglionic neurons end at capillaries
that carry their secretions to the bloodstream).
 
3. The sympathetic division shows extensive divergence; a single preganglionic
fiber may innervate as many as 32 ganglionic neurons in several different
ganglia (here's the 1:32 ratio again). As a result, a single sympathetic
motor neuron inside the CNS can control a variety of peripheral effectors and
produce a complex and coordinated response.
 
4. All preganglionic neurons release ACh at their synapses with ganglionic
neurons. Most of the postganglionic fibers release NE, but a few release ACh.
 
5. The effector response depends on the function of the membrane receptor
activated when epinephrine (E) or norepinepherine (NE) binds to either alpha
or beta receptors.


The Parasympathetic Division (Christine's division)
 
The parasympathetic division of the ANS includes the following:
 
1. Preganglionic neurons located in the brain stem and in sacral segments:
In the brain, the mesencephalon, pons, and medulla oblongata contain autonomic
nuclei associated with cranial nerves III, VII, IX and X. In the sacral
segments of the spinal cord, the autonomic nuclei lie is spinal segments
S2-S4.
 
2. Ganglionic neurons in peripheral ganglia located very close to -  or even
within - the target organs:
As a result, the effects of parasympathetic stimulation are more specific and
localized than those of the sympathetic division.
 
ORGANIZATION AND ANATOMY OF THE PARASYMPATHETIC DIVISION
 
Parasympathetic preganglionic fibers leave the brain in cranial nerves III,
VII, IX and X. These preganglionic fibers synapse in the ciliary,
pterygopalatine, submandibular, and otic ganglia. Short postganglionic fibers
then continue to their peripheral targets. The vagus nerve provides
preganglionic parasympathetic innervation to intramural ganglia within
structures in the thoracic cavity and in the abdominopelvic cavity as distant
as the last segments of the large intestine. The vagus nerve alone provides
roughly 75% of all parasympathetic outflow. The sacral parasympathetic outflow
does not join the ventral rami of the spinal nerves. Instead, the
preganglionic fibers form distinct pelvic nerves that innervate intramural
ganglia in the kidney and urinary bladder, the terminal portions of the large
intestine, and the sex organs.
 
For the general functions of the parasympathetic division, check out
Christine's story. The parasympathetic division has been called the anabolic
system because stimulation leads to a general increase in the nutrient content of
the blood.
 
Ok pay attention to this:
 
All of the preganglionic and postganglionic fibers in the parasympathetic
division release ACh at their synapses and neuroeffector junctions. Read more
about that on page 456.
 
Two different types of ACh receptors are found on postsynaptic membranes:
 
Nicotinic receptors are found on the surfaces of all ganglionic neurons of
both the parasympathetic and the sympathetic divisions, as well as the
neuromuscular junctions of the SNS. Exposure to ACh ALWAYS causes excitation
of the ganglionic neuron or muscle fiber through the opening of membrane ion
channels.
 
 
Muscarinic receptors are found at all cholinergic neuroeffector junctions in
the parasympathetic division, as well as at the few cholinergic neuroeffector
junctions in the sympathetic divisions. Stimulation of muscarinic receptors
produces longer-lasting effects than does stimulation of nicotinic receptors.
The response, which reflects the activation or inactivation of specific
enzymes, may be either excitatory or inhibitory.
 
Summary of the Parasympathetic Division
 
1. The parasympathetic division includes visceral motor nuclei in the brain
stem associated with four cranial nerves (III, VII, IX and X). In sacral
segments S2-S4, autonomic nuclei lie in the lateral portions of the anterior
gray horns.
 
2. The ganglionic neurons are situated in intramural ganglia or in ganglia
closely associated with their target organs.
 
3. The parasympathetic division innervates structures in the head and organs
in the thoracic and abdominopelvic cavities.
 
4. All parasympathetic neurons are cholinergic.
 
5. The effects of parasympathetic stimulation are usually brief and restricted
to specific organs and sites.
 
 Dual Innervation
 
Most vital organs receive dual innervation, that is they receive instructions
from both the sympathetic and parasympathetic divisions. When dual innervation
exists, the two divisions often have opposing or antagonistic effects.
 
Visceral Reflexes
 
Visceral reflexes are the simplest functional units in the autonomic nervous
system. They provide automatic motor responses that can be modified,
facilitated, or inhibited by higher centers, especially those of the
hypothalamus.
 
Each visceral reflex arc consists of a receptor, a sensory nerve, a processing
center, and two visceral motor neurons.
 
An example of a visceral reflex is when someone shines a light in your eye.
Check out page 459 for details.
 
Visceral reflexes may be either long reflexes or short reflexes. Long reflexes
are the autonomic equivalents of the polysynaptic reflexes in Chapter 13.
Visceral sensory neurons deliver information to the CNS along the dorsal roots
of spinal nerves, within the sensory branches of cranial nerves, and within
the autonomic nerves that innervate visceral effectors. The processing steps
involve interneurons within the CNS, and the motor neurons involved are located
within the brain stem or spinal cord.
 
Short reflexes bypass the CNS entirely; they involve sensory neurons and
interneurons whose cell bodies are located within autonomic ganglia. The
interneurons synapse on ganglionic neurons, and the motor commands are then
distributed by postganglionic fibers. Short reflexes control very simple motor
responses with localized effects. In general, short reflexes may control
patterns of activity in one small part of a target organ, whereas long
reflexes coordinate the activities of the entire organ.
 
KNOW FIGURE 17.12
 
 
Ok everyone, that's all for Chapter 17. I apologize for taking so long to get
the blog up, I just wanted to make sure I had everything outlined three times
before I put anything up. Like Dr. Mazurkie says, we gamble every time we leave
something out. I think I pretty much covered all I can for this chapter. The
next blog will be on Chapter 19, and will be up on Monday. Hope everyone has a
great weekend!!

Again, any questions, comments, suggestions, corrections, etc can be e-mailed to me at hcha0243@postoffice.uri.edu

Ok, here’s the last chapter that’s going to be on the exam. Let’s check it out!

Receptors:

A sensory receptor is a specialized cell or cell process that monitors conditions in the body or the external environment. Stimulation of the receptor directly or indirectly alters the production of action potentials in a sensory neuron.

Sensation: The sensory information arriving at the CNS.

Perception: a conscious awareness of a sensation

 
General senses: sensations of temperature, pain, touch, pressure, vibration and proprioception (body position).

General sensory receptors are distributed throughout the body. These sensations arrive at the primary sensory cortex (or somatosensory cortex) via pathways that the book already told us about (p 426) but that we didn’t have to read.

 
Special senses: smell (olfaction), taste (gustation), balance (equilibrium), hearing and vision. The sensations are provided by specialized receptor cells that are structurally more complex than those of the general senses. These receptors are located within complex sense organs, like your eyes and ears.

 Each receptor has a characteristic sensitivity. For example, a touch receptor is very sensitive to pressure but relatively insensitive to chemical stimulus (this is called receptor specificity). Specificity results from the structure of the receptor cell itself or from the presence of accessory or structures that shield it from other stimuli.

 Receptive field: the area monitored by a single receptor cell (check out page 467 figure 18.1).

 
Different types of sensory neurons:

Tonic receptors- always active, ex. photoreceptors of the eye and various receptors that monitor body position

Phasic receptors- receptors that are normally inactive but become active for a short time whenever there is a change in the conditions they are monitoring. These also provide information on the intensity and rate of change of a stimulus.

 (more about tonic and phasic receptors in a second)

 Adaptation is a reduction in sensitivity in the presence of a constant stimulus. (It was also a movie starring Nicholas Cage and Ron Livingston).  Peripheral (sensory) adaptation occurs when the receptors or sensory neurons alter their levels of activity. The receptor responds strongly at first, but then the activity along the afferent fiber gradually declines (in part due to synaptic fatigue). This would be a characteristic of phasic receptors (or fast-acting receptors). Tonic receptors show little peripheral adaptation and are called slow-adapting receptors.

 Central adaptation: conscious awareness of a stimulus virtually disappears, although the sensory neurons are still active. At the subconscious level, central adaptation further restricts the amount of detail arriving at the cerebral cortex.

 General Senses

(I’m going to list them, then go into more detail later)

 Exteroceptors: provide information about the external environment

Proprioceptors: monitor body position

Interoceptors: monitor conditions inside the body

 
Here are four types according to the nature of the stimulus that excites them.

Nociceptors respond to a variety of stimuli usually associated with tissue damage. Receptor activation causes the sensation of pain.

Thermoreceptors respond to changes in temperature.

Mechanoreceptors: stimulated or inhibited by physical distortion, contact, or pressure on their cell membranes.

Chemoreceptors: monitor the chemical composition of body fluids and respond to the presence of specific molecules.

 
Here’s the more detail I was telling you about.

 
Nociceptors (pain receptors)

 Three types: 1. receptors sensitive to extremes of temperature

                     2. receptors sensitive to mechanical damage

                     3. receptors sensitive to dissolved chemicals (such as those released by injured cells)

Fast pain (prickling pain) is produced by deep cuts or similar injuries.

Slow pain (burning and aching pain) result from the same types of injuries as fast pain, but sensations of slow pain begin later and persist longer than sensations of fast pain.

 
Thermoreceptors: these respond to changes in temperature (as mentioned earlier), they are phasic, and are very active when the temperature is changing, but quickly adapt to a stable temperature.

 
Mechanoreceptors: broken down into three classes

1. Tactile receptors which provide sensations of touch, pressure, and vibrations.
2. Baroreceptors detect pressure changes in the walls of blood vessels and in portions of the digestive, reproductive, and urinary tracts
3. Proprioceptors monitor the positions of joints and muscles. They’re the most complex of the general sensory receptors.

A quick word on tactile receptors:

 Fine touch and pressure receptors provide detailed information about a source of stimulation, including its exact location, shape, size, texture, and movements.

Crude touch and pressure receptors provide poor localization and little additional information about the stimulus.

 Tactile corpuscles are found where tactile sensitivities are extremely well developed.

Ruffini corpuscles are tonically active and show little, if any, adaptation.

Lamellated corpuscles respond to deep pressure but are most sensitive to pulsing or vibrating stimuli.

 
Baroreceptors (think barometer) are stretch receptors that monitor changes in pressure.

 
I’m not writing anything about Proprioceptors because all the book keeps saying over and over is that they monitor the position of joints and muscles.

Chemoreceptors are specialized neurons that can detect small changes in the concentration of specific chemicals or compounds.

On to…

Olfaction (sense of smell) is provided by paired olfactory organs. The olfactory epithelium covers the inferior surface of the cribriform plate and the superior portions of the nasal septum and superior nasal conchae of the ethmoid.

Gustation (taste) provides information about the foods and liquids we consume. (For some reason, that definition just cracks me up). Gustatory receptors are distributed over the dorsal surface of the tongue and adjacent portions of the pharynx and larynx.

 There are three different types of epithelial projections called papillae, filiform, fungiform and circumvallate, all located on the tongue.

 Taste sensations include sweet, salty, sour and bitter, and then the new ones, umami and water. (I know, I still disagree that water tastes like anything.)

EQUILIBRIUM AND HEARING (I’m very excited about these)

Let’s talk about the ear.

 It divides into three regions: the external ear, the middle ear, and the inner ear.

 External ear: This is the visible portion of the ear. It collects and directs sound waves to the eardrum. It includes the auricle, which is supported by elastic cartilage. The auricle surrounds the external acoustic meatus, protecting it. The eardrum has three names, eardrum, tympanic membrane, or tympanum.

 
Tympanic membrane- very delicate. It needs a lot of protection. Ceruminous glands distributed along the external acoustic meatus secrete a waxy material, and many small, outwardly projecting hairs help deny access to foreign objects or insects. The waxy secretion of the ceruminous glands (called cerumen) also slows the growth of microorganisms in the external acoustic meatus and reduces the chances of infection.

 
Middle ear: consists of an air-filled space (the tympanic cavity) which contains the auditory ossicles, three tiny ear bones called malleus, incus, and stapes. These also happen to be the smallest bones in the body. These bones act as levers that transfer sound vibrations from the tympanum to a fluid-filled chamber within the ear.

Quick description: the malleus is shaped like a hammer, the incus is shaped like an anvil, and the stapes are like stirrups (this one is easy for the ladies to remember).

 
There are also two small muscles that protect the eardrum and ossicles from violent movements under very noisy conditions.

 
Tensor tympani muscle- short ribbon of muscle whose origin is the petrous part of the temporal bone, within the musculotubal canal, and whose insertion is on the “handle” of the malleus. When the tensor tympani contracts, the malleus is pulled medially, stiffening the tympanum. This increased stiffness reduces the amount of possible movement.

Stapedius muscle- originates from the posterior wall of the tympanic cavity and inserts on the stapes. Contraction of the stapedius pulls the stapes, reducing movement of the stapes at the oval window.

 
Inner Ear: (quick note, figure 18.11 is actually a pretty good table to learn these with)

The senses of equilibrium and hearing are provided by the receptors of the inner ear. These receptors are housed within a collection of fluid-filled tubes and chambers known as the membranous labyrinth, which contains a fluid called endolymph.

The bony labyrinth is a shell of dense bone that surrounds and protects the membranous labyrinth. Between the bony and membranous labyrinths flows the perilymph, a liquid whose properties closely resemble the CSF.

 The bony labyrinth can be subdivided into the vestibule, semicircular canals, and cochlea. The cavity within the vestibule contains a pair of membranous sacs, the utricle and the saccule. The cochlea contains a slender, elongated portion of the membranous labyrinth called the cochlear duct.

 The outer walls of the perilymphatic chambers consist of dense bone everywhere except at two small areas near the base of the cochlear spiral openings. The round window is the more inferior of the two, and the oval window is the more superior of the two.

 
Hair cells. These are very important. These are sensory receptors of the inner ear, are surrounded by supporting cells and are monitored by sensory afferent fibers. Hair cells are highly specialized mechanoreceptors sensitive to the distortion of their stereocilia (the stereocilia attach to nerve cells). More on hair cells in a bit.

 
Vestibular Complex:

 The vestibular complex is the part of the inner ear that provides equilibrium sensations by detecting rotation, gravity, and acceleration. It consists of semicircular canals, the utricle and saccule.

 The anterior, posterior, and lateral semicircular canals are continuous with the vestibule. Each semicircular canal surrounds a semicircular duct. The duct contains a swollen region (the ampulla) which contains the sensory receptors.

Ok, back to hair cells. Hair cells attached to the wall of the ampulla form a raised structure known as a crista. In addition to its stereocilia, each hair in the vestibule also contains a kinocilium (a single large cilium). Hair cells do not actively move their kinocilia and stereocilia. However, when an external force pushes against these processes, the distortion of the cell membrane alters the rate of chemical transmitter released by the hair cell.

 The kinocilia and stereocilia of the hair cells are embedded in a gelatinous structure, the cupula. Remember that hair cells move in response to fluid.

 The receptors within each semicircular duct respond to one of three rotational movements. A horizontal rotation (like when you shake your head “no”) stimulates the hair cells of the lateral semicircular duct. Nodding “yes” excites the anterior duct, while tilting the head from side to side activates the receptors in the posterior duct.

 
The Utricle and Saccule

 
A slender passageway continuous with the narrow endolymphatic duct connects the utricle and saccule. The endolymphatic duct ends in a blind pouch, known as an endolymphatic sac, which projects through the dura mater lining the temporal bone and into the subdural space. The hair cells of the utricle and saccule are clustered in the oval maculae. Just like in the ampullae, the hair cell processes are embedded in a gelatinous mass. The surface of this gelatinous material contains densely packed calcium carbonate crystals known as statoconia. The complex as a whole (gelatinous matrix and statoconia) is called an otolith. Check out page 481 for some pretty cool facts on the otolith.

 
Hair cells of the vestibule and semicircular ducts are monitored by sensory neurons located in adjacent vestibular ganglia. Sensory fibers from each ganglion form the vestibular branch of the Vestibulocochlear nerve.

Cochlea

 The bony cochlea coils around a central hub, or modiolus. The modiolus encloses the spiral ganglion, which contains the cell bodies of the sensory neurons that monitor the receptors in the cochlear duct. The hair cells of the cochlear duct are found in the organ of Corti, or spiral organ. This sensory structure rests on the basilar membrane that separates the cochlear duct from the tympanic duct. If there is damage to the cochlea you could lose the ability to hear high and low frequencies.

 
Hair cell stimulation activates sensory neurons whose cell bodies are in the adjacent spiral ganglion. Their afferent fibers form the cochlear branch of the Vestibulocochlear nerve.

Steps in the Production of an Auditory Sensation

1. Sound waves arrive at the tympanic membrane.
2. Movement of the tympanic membrane causes displacement of the auditory ossicles
3. Movement of the stapes at the oval window establishes pressure waves in the perilymph of the vestibular duct.
4. The pressure waves distort the basilar membrane on their way to the round window of the tympanic duct.
5. Vibration of the basilar membrane causes vibration of hair cells against the tectorial membrane, resulting in hair cell stimulation and neurotransmitter release.
6. Information concerning the region and intensity of stimulation and is relayed to the CNS over the cochlear branch of N VIII.

Ok, I’m not doing the eye, and there is a reason for it. I just want to take a second to wish everyone the best of luck on the exam tomorrow; I know we’re all going to do great!

Let me start out by saying I hope everyone is doing well, enjoying their long weekend. Now get your asses back to studying!!!

Cranial Nerves

There’s no easy way to tell you all this, but we have to know everything about the nerves for the exam on Wednesday. It’s true. Now, before you start to panic, I’m actually giving you a blog dedicated to the nerves. I’m going to give you the name, number, primary function, origin, where it passes through, and it’s destination (plus any smart ass comments I may have). And, just in case, I know that you all probably already know roman numerals, but I’m going to give you a quick breakdown. Hey, you never know, someone might not know. Then they’d be screwed.

I                  is equal to           one                  is equal to            Olfactory

II                is equal to            two                  is equal to            Optic

III               is equal to           three                is equal to             Oculomotor

IV               is equal to           four                 is equal to              Trochlear

V                 is equal to          five                 is equal to              Trigeminal

VI                is equal to          six                  is equal to              Abducens

VII              is equal to           seven              is equal to            Facial

VIII             is equal to          eight               is equal to              Vestibulocochlear

IX               is equal to           nine                is equal to           Glossopharyngeal

X                is equal to            ten                      is equal to             Vagus

XI               is equal to          eleven            is equal to               Accessory

XII              is equal to          twelve            is equal to              Hypoglossal

(Study tip: When learning these, play the song “Thnks fr th Mmrs” by Fall Out Boy. You will totally see how it works.)

Olfactory Nerve (N I)

Primary function: Special sensory (smell)

Origin: Receptors of olfactory epithelium

Passes through: Cribriform plate of ethmoid

Destination: Olfactory bulbs

Lots of olfactory words in here. Look at the name, origin, and destination.

Optic Nerve (N II)

Primary function: Special sensory (vision)

Origin: Retina of the eye

Passes through: Optic canal of sphenoid

Destination: Diencephalon by way of the optic chiasm

I’m pretty sure Dr. Mazurkie wants us to know about the optic chiasm, which is the crossing point of the optic nerves.

Oculomotor Nerve (N III)

Primary function: Motor, eye movements

Origin: Mesencephalon

Passes through: Superior orbital fissure of sphenoid

Destination: Somatic motor: superior, inferior, and medial rectus muscles; the inferior oblique muscle, the levator palpebrae superioris muscle.         Visceral motor: intrinsic eye muscles

I’ve got nothing on this one.

Trochlear Nerve (N IV)

Primary function: Motor, eye movements

Origin: Mesencephalon

Passes through: Superior orbital fissure of sphenoid

Destination: Superior oblique muscle

Look at how similar these two are (the Oculomotor and Trochlear). Same primary function, same origin, and they pass through the same place.

Trigeminal Nerve (NV)

 Primary function: Mixed (sensory and motor); ophthalmic and maxillary branches sensory, mandibular branch mixed

Origin: Ophthalmic branch (sensory); orbital structures, nasal cavity, skin of forehead, superior eyelid, eyebrow, and part of the nose

            Maxillary branch (sensory) inferior eyelid, upper lip, gums, and teeth; cheek; nose, palate and part of the pharynx

            Mandibular branch (mixed) sensory from lower gums, teeth, and lips; palate and tongue (part) motor from motor nuclei of pons

Passes through: Ophthalmic branch through superior orbital fissure, maxillary branch through foramen rotundum, mandibular branch through foramen ovale.

Destination: Ophthalmic, maxillary and mandibular branches to sensory nuclei in the pons, mandibular branch also innervates muscles of mastication.

Yes. Remember the Trigeminal nerve consists of three branches, ophthalmic, maxillary and mandibular. The rest of this stuff is just crazy.

Abducens Nerve (N VI)

Primary function: Motor, eye movement

Origin: Pons

Passes through: Superior orbital fissure of sphenoid

Destination: lateral rectus muscle

This is actually one of my favorite nerves. First of all, it has a pretty name (the celebs will all be naming their children after cranial nerves instead of fruit (hi Apple!) Did you know that Jason Lee (from My Name is Earl and all of Kevin Smith’s movies actually named his child Pilot Inspektor. Jason Lee is awesome, so he can get away with it).  Anyway, along with it’s pretty name, it has very easy to remember function, origin, passes through, and destination. Seriously, compare it to the Trigeminal nerve.

 
Facial Nerve (N VII)

Primary function: Mixed (sensory and motor)

Origin: Sensory from taste receptors on anterior two-thirds of the tongue; motor from motor nuclei of pons

Passes through: Internal acoustic meatus of temporal bone, along facial canal to reach stylomastoid foramen

Destination: Sensory to sensory nuclei of pons

                    Somatic motor: muscles of facial expression

                    Visceral motor: lacrimal (tear) gland and nasal mucous glands via pterygopalatine ganglion, submandibular and sublingual salivary glands via submandibular ganglion

 
Ok, seriously. I think anatomists were just “wrecked” when they came up with some of these words. Pterygopalatine. My hypothesis is that they just wanted to put names together to come up with one bigger name. I’m aware that it does help us remember where things come from, but really, pterygopalatine.

Vestibulocochlear Nerve (N VIII)

Primary function: Special sensory; balance and equilibrium (vestibular branch) and hearing (cochlear branch)

Origin: Receptors of the inner ear (vestibule and cochlea)

Passes through: Internal acoustic meatus of the temporal bone

Destination: Vestibular and cochlear nuclei of pons and medulla oblongata

 
This is one of the times I was talking about, when putting two words together CAN help (although the words are still silly). Vestibulocochlear is the combination of vestibule and cochlea, and check out the primary function and origin. This also may be important because it has to do with balance and equilibrium.

Glossopharyngeal Nerve (N IX)

Primary function: Mixed (sensory and motor)

Origin: Sensory from posterior one-third of the tongue, part of the pharynx and palate, the carotid arteries of the neck, motor from motor nuclei

Passes through: Jugular foramen between occipital and temporal bones

Destination: Sensory fibers to sensory nuclei of medulla oblongata

                    Somatic motor: pharyngeal muscles involved in swallowing

                    Visceral motor: parotid salivary gland, after synapsing in the otic ganglion

 
Again, I got nothing.


Vagus Nerve (N X)

Primary function: Mixed (sensory and motor)

Origin: Visceral sensory from pharynx (part), auricle, external acoustic meatus, diaphragm, and visceral organs in thoracic and abdominopelvic cavities

Visceral motor: from motor nuclei in the medulla oblongata

Passes through: Jugular foramen between occipital and temporal bones

Destination: Sensory fibers to sensory nuclei and autonomic centers of medulla oblongata

                    Somatic motor to muscles of the palate and pharynx

                    Visceral motor to respiratory, cardiovascular, and digestive organs in the thoracic and abdominal cavities

Ok, I have to say it. What happens in Vagus stays in Vagus. But seriously, remember that it is involved with digestion, respiration, and heart rate.


Accessory Nerve (N XI)

Primary function: Motor

Origin: Motor nuclei of spinal cord and medulla oblongata

Passes through: Jugular foramen between occipital and temporal bones

Destination: Internal branch innervates voluntary muscles of palate, pharynx, and larynx: external branch controls sternocleidomastoid and trapezius muscles.

 
I’m still getting over my Vagus joke.

Hypoglossal Nerve (N XII)

Primary function: Motor, tongue movements

Origin: Motor nuclei of the medulla oblongata

Passes through: Hypoglossal canal of occipital bone

Destination: Middle of the tongue

 
Stick out your tongue while reading the Hypoglossal facts. There, you’ll remember it better now.

That's about all I've got to say on those. I'll be back with Chapter 18 soon!

Yay!  We made it to the brain! Let’s start by looking at how it’s formed.

The central nervous system starts as a hollow neural tube, with a fluid-filled internal cavity called the neurocoel. In the fourth week of development, three areas in the cephalic portion of the neural tube enlarge rapidly through expansion of the neurocoel. This enlargement creates three prominent primary brain vesicles, which are named for their relative positions.

1. The prosencephalon (or forebrain)
2. The mesencephalon (or midbrain)
3. The rhombencephalon (or hindbrain).

These divisions actually divide further. The prosencephalon (forebrain) and rhombencephalon (hindbrain) are subdivided further, forming secondary brain vesicles. The prosencephalon (forebrain) forms the telencephalon and the diencephalon. The telencephalon forms the cerebrum.

The hollow diencephalon is kind of like a house. It has a roof (the epithalamus), walls (the left and right thalamus) and a floor (the hypothalamus). The portion of the rhombencephalon (hindbrain) closest to the mesencephalon (midbrain) forms the metencephalon. The ventral portion of the metencephalon develops into the pons, and the dorsal portion becomes the cerebellum. The portion of the rhombencephalon (hindbrain) closer to the spinal cord becomes the myelencephalon, which will form the medulla oblongata.

Now, the major regions and landmarks.

There are six major divisions in the adult brain:

1. The cerebrum
2. The diencephalon
3. The mesencephalon
4. The pons
5. The cerebellum
6. The medulla oblongata

 
The cerebrum is divided into large, paired cerebral hemispheres, separated by the longitudinal fissure. This is where the conscious thought processes, intellectual functions, memory storage and retrieval and complex motor patters originate.

 
The diencephalon is the deep portion of the brain attached to the cerebrum. It has three subdivisions (which I mentioned earlier, but now we’re going to learn what they do).

1. The epithalamus contains the hormone-secreting pineal gland (which is an endocrine structure)
2. The thalamus (both right and left) are sensory information relay and processing centers.
3. The hypothalamus is a visceral control center. This division contains centers involved with emotions, autonomic functions, and hormone production. It’s the primary link between the nervous and endocrine systems. 

The remaining regions of the brain are collectively known as the brain stem. This consists of the mesencephalon, pons, and medulla oblongata. The brain stem contains important processing centers and also relays info to or from the cerebrum or cerebellum.

The mesencephalon (midbrain) process visual and auditory information and coordinate and direct reflexive somatic motor responses to these stimuli. It also contains centers involved with the maintenance of consciousness.

The pons is immediately inferior to the mesencephalon. It contains nuclei involved with both somatic and visceral motor control. The term pons refers to a bridge, and the pons connects the cerebellum to the brain stem. The cerebellum automatically adjusts motor activities on the basis of sensory information and memories of learned patterns of movement.

The medulla oblongata relays sensory information to the thalamus and to other brain stem centers. It also contains major centers concerned with the regulation of autonomic function, such as heart rate, blood pressure, and digestive activities. The superior portion of the medulla oblongata has a thin, membranous roof, and the inferior portion resembles the spinal cord.

Organization of gray and white matter in the brain stem:

The general distribution of the gray matter in the brain stem resembles that of the spinal cord, in that there is an inner region of gray matter surrounded by tracts of white matter. The gray matter surrounds the fluid filled ventricles and passageways that correspond to the central canal of the spinal cord. Although tracts of white matter are present, the arrangement is not as predictable as it is in the spinal cord. In the cerebrum and cerebellum, the white matter is covered by neural cortex, which is a superficial layer of gray matter.

Ventricles are fluid-filled cavities (like the oceans) within the brain. They are filled with CSF and lined with ependymal cells. There are four ventricles in the brain, one within each cerebral hemisphere, a third in the diencephalon, and the fourth lies between the pons and cerebellum and extends into the superior portion of the medulla oblongata.The lateral ventricles in the cerebral hemisphere are separated by the septum pellucidum. The cavity within the diencephalon is known as the third ventricle. The third and fourth ventricles are connected by a slender canal known as the aqueduct of the midbrain. The fourth ventricle goes into cerebral canal of the spinal cord.

MENINGES! I just love that word. The cranial meninges provide protection; act as shock absorbers that prevent contact with surrounding bones. These are like the spinal meninges, because they have the same three layers: the dura mater, arachnoid mater, and pia mater.

The cranial dura mater is made of up two fibrous layers. The outermost layer (or endosteal layer) is fused to the periosteum lining the cranial bones. The innermost layer is called the meningeal layer.

 
There are four locations in the meningeal layer of the cranial dura mater where they extend deep into the cranial cavity.

1. The falx cerebri is a fold of dura mater that projects between the cerebral hemispheres in the longitudinal fissure. Two large venous sinuses, the superior saggittal sinus and inferior saggittal sinus travel within this fold.
2. The tentorium cerebelli separates and protects the cerebellar hemispheres from those of the cerebrum. The transverse sinus lies within the tentorium cerebelli.
3. The falx cerebelli extends in the midsaggittal line inferior to the tentorium cerebelli, dividing the two cerebellar hemispheres.
4. The diaphragma sellae is a continuation of the dural sheet that lines the sella turcica of the sphenoid.

Arachnoid Mater- just a couple quick things:

 Deep to the arachnoid mater is the subarachnoid space, which contains a delicate, web like meshwork of collagen and elastic fibers that link the arachnoid mater to the underlying pia mater. There are also arachnoid granulations, which are where fingerlike extensions of the cranial arachnoid mater penetrate the dura mater. At these projections, cerebrospinal fluid flows past bundles of fibers (the arachnoid trabeculae) crosses the arachnoid mater, and enters the venous circulation.

The cranial pia mater is tightly attached to the surface contours of the brain, following its contours and lining the sulci. The pia is anchored to the surface of the brain by the processes of astrocytes.

We’re now going to look at the Blood-Brain Barrier a little more closely:

The barrier provides a means to maintain a constant environment, which is necessary for both control and proper functioning of CNS neurons. The BBB remains intact throughout the CNS, except in three places (check out page 385 for the full description).

Cerebrospinal Fluid

 Cerebrospinal fluid completely surrounds and bathes the exposed surfaces of the central nervous system. As I mentioned earlier, it has several important functions.

1. Cushioning delicate neural structures
2. Supporting the brain
3. Transporting nutrients, chemical messengers, and waste products.

The choroids plexus (which consist of a combination of specialized ependymal cells and permeable capillaries) is responsible for the production of cerebrospinal fluid.

Cerebrum

 The cerebrum is the largest region of the brain. Remember that it consist of the paired cerebral hemispheres, which rest on the diencephalon and brain stem. A thick blanket of neural cortex covers the cerebral hemispheres that form the superior and lateral surfaces of the cerebrum. The cortical surface forms a series of elevated ridges, or gyri, separated by shallow depressions, called sulci or deeper grooves, called fissures.

The Cerebral Lobes:

 The book tells us to remember these three facts about the lobes

1. Each cerebral hemisphere receives sensory information from and generates motor commands to the opposite side of the body.
2. The two hemispheres have some functional differences, although anatomically they appear to be identical.
3. The assignment of a specific function to a specific region of the cerebral cortex is imprecise.

 Ok, a quick breakdown of the lobes and what they do (look at table 15.2)

 Frontal lobe- conscious control of skeletal muscles

Parietal lobe- conscious perception of touch, pressure, vibration, pain, temperature and taste

Occipital lobe- conscious perception of visual stimuli

Temporal lobe- conscious perception of auditory and olfactory stimuli

All lobes- integration and processing of sensory data, processing and initiation of motor activities.

Central White Matter

 The central white matter is covered by the gray matter of the cerebral cortex. It contains myelinated fibers that form bundles that extend from one cortical area to another that connect areas of the cortex to other regions of the brain. There are three kinds:  

1. Association fibers
2. Commissural fibers
3. Projection fibers

 
Association fibers interconnect portions of the cerebral cortex within the same cerebral hemisphere. Remember that the arcuate fibers are the shortest association fibers, and they curve in an arc. The longer association fibers are the longitudinal fasciculi, and are used for long distance communication. Table 15.3 has a pretty good description of these.

 Basal Nuclei are paired masses of gray matter within the cerebral hemispheres. There’s more, but Chapter 15 is so long that it’s already going to be two blogs, so I’m going to move on to….

 
The Limbic System

 The function of the limbic system include

1. Establishment of emotional states and related behavioral drives
2. The linking of conscious, intellectual functions of the cerebral cortex with the unconscious and autonomic functions of other portions of the brain
3. Facilitating memory storage and retrieval

Check out table 15.5 for a breakdown of all the components.

 
Diencephalon

 The diencephalon connects the cerebral hemispheres to the brain stem. It consists of the epithalamus, thalamus (left and right) and the hypothalamus. The posterior portion of the epithalamus contains the pineal gland, which is an endocrine structure that secretes the hormone melatonin. For those of you who were not already aware of this, melatonin is involved in the regulation of the day-night cycles.

 
The thalamus processes and relays sensory information. Check out table 15.6 for more info.

 
Hypothalamus contains centers involved with emotions and visceral processes that affect the cerebrum as well as other components of the brain stem. It also controls a variety of autonomic functions and forms a link between the nervous and endocrine systems.

 
The functions of the hypothalamus:

1. Subconscious control of skeletal muscle contractions
2. Control of autonomic functions
3. Coordination of activities of the nervous and endocrine systems
4. Secretions of hormones: antidiuretic (restricts water loss at the kidneys) and oxytocin (stimulates smooth muscle contractions in uterus and prostate gland, and myoepithelial cell contractions in mammary glands)
5. Production of emotions and behavioral drives
6. Coordination between voluntary and autonomic functions
7. Regulation of body temperature
8. Control of circadian rhythms

The Pons

 This extends inferior from the mesencephalon to the medulla oblongata. It contains:

1. Sensory and motor nuclei for four cranial nerves
2. Nuclei concerned with the involuntary control of respiration
3. Nuclei that process and relay cerebellar commands arriving over the middle cerebellar peduncles
4. Ascending, descending, and transverse tracts

 Keep in mind that the pneumotaxic center and apneustic center are important for breathing.

 
The Cerebellum

This has two primary functions: adjusting the postural muscles of the body and programming and fine tuning voluntary and involuntary movements.

The Medulla Oblongata

 The medulla oblongata physically connects the brain with the spinal cord, and all communication between the brain and the spinal cord involves tracts that ascend or descend through the medulla oblongata.

 
Nuclei in the medulla oblongata may be:

1. Relay stations
2. Nuclei of cranial nerves
3. Autonomic nuclei

 
Ok, I know that the cranial nerves are a part of this chapter. However, because they are so important, they are actually getting their own blog.

As mentioned earlier, if you have any compliments, questions, suggestions (but not complaints, I don’t have time to read any bitching, time is of the essence here!) please e-mail me at hcha0243@postoffice.uri.edu.