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A&P Course Objectives - Exam 3


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List the statistics associated with cardiovascular disease.
1. cardiovascular disease is the #1 killer in the US

2. 40% of the deaths each year in the US are from cardiovascular disease

3. 25% of people in US have some form of cardiovascular disease

4. coronary heart disease of bo the most prevalent cause of death in US

5. 60% of body weight is water

6. most of the water is in the cells with least in plasma
What is the distribution of body water?
Body water is approximately 60% of body weight and this is distributed among:

- intracellular (30 liters)
- interstitial (12 liters)
- plasma spaces (3 liters)
Describe the shape and size of the heart and indicate its orientation in the thorax.
What is the structure and function of the coverings of the heart?
What are the three layers of the heart? How does one layer relate to the visceral pericardium?
Describe the structure and basic functions of each heart chamber. What vessels are associated with each? How can you distinguish between the right and left ventricles?
What are the two types of heart valves and what are their structural differences?
Name the four heart valves and describe their mechanism of operation.
Trace the pathway of blood through the heart.
What purpose is served by the cardiac or fibrous skeleton?
Describe the coronary circulation (origin, branches, pathway to general circulation). When in the cardiac cycle does the majority of the coronary blood flow occur?
What are some of the common terms associated with coronary artery disease?
What is the response to injury theory of atherosclerosis?
Describe the structural and functional properties of cardiac muscle. How do these properties differ from skeletal muscle?

(covered in Dr. Walronds section)
Review the events of cardiac muscle contraction.

(Dr. Walrond's section)
Sing the "Pump Your Blood" song.
Pump, pump, pumps your Blood.

The right atrium’s where the process begins, where the CO2 Blood enters the heart.

Through the tricuspid valve, to the right ventricle, the pulmonary artery, and lungs.

Once inside the lungs, it dumps its carbon dioxide and picks up its oxygen supply.

Then it’s back to the heart through the pulmonary vein, through the atrium and left ventricle.

Pump, pump, pumps your Blood.


Pump, pump, pumps your Blood.

The aortic valve’s, where the Blood leaves the heart, then it's channeled to the rest of the bod.

The arteries, arterioles, and capillaries too bring the oxygenated Blood to the cells.

The tissues and the cells trade off waste and CO2, which is carried through the venules and the veins

Through the larger vena cava to the atrium and lungs, and we're back to where we started in the heart.

Pump, pump, pumps your Blood.
What are the components of the cardiac electrical conduction system? Trace the normal sequence of events.
Describe the basis for the electrical properties of the pacemaker and non-pacemaker cells.
Describe the basis for electrocardiography and examples of clinical application.
Describe the role of the sympathetic and parasympathetic nervous system in modifying the conduction system and contractility of the heart. What neurotransmitters are involved? What is the basis for the neurotransmitter action?
Summarize the events of the cardiac cycle using a figure such as the one on page 739 of your textbook.
Describe the physical basis for normal heart sounds and provide specific examples of heart murmurs and their specific timing relative to the cardiac cycle (systole or disstole). What are the consequences of heart murmurs?
What are indicators of your cardiac performance? How is your cardiac performance modified? Be able to demonstrate changes in cardiac performance using pressure-volume curves for the ventricle.
The QRS complex of the ECG appears as the:

a. atria depolarize
b. ventricles depolarize
c. ventricles repolarize
d. atria repolorize
e. b and d
During the cardiac cycle, the amount of blood remaining in the ventricle when the atrioventricular valve closes is the:

a. end-diastolic volume
b. stroke volume
c. cardiac output
d. end-systolic volume
e. ejection refractio
The majority of the blood flowing to the microvascular of the musculature of the left ventricle occurs during:

a. systole
b. isovolumetric contraction
c. ventricular filling
d. isovolumetric relaxation
e. a and b
The majority of the water in your body is found in:

a. interstitial space
b. plasma
c. intracellular space
d. cell membranes
e. red blood cells
c. intracellular space
The decline in stroke volume occurring as a result of enhanced vascular resistance is due to:

a. increased afterload
b. increased preload
c. decreased preload
d. increased contractility
e. decreased afterload
How is arterial blood pressure maintained fairly constant? What are the target organs? What centers in the brain are involved? What detectors are in play for this negative feedback mechanism?
What are the three layers of a typical blood vessel? What is the function of each?
Which vessels comprise the microcirculation? What is a capillary bed?
Describe how the structure of arteries and veins differ. What are the basic functions of each?
Define vasoconstriction and vasodilation.
Mathematically, how are blood flow, blood pressure, vascular dimensions and blood viscosity related? What is this relationship called?
What is the difference between blood velocity and blood flow?
How do blood velocity, blood pressure and cross-sectional area vary among the various types of vessels?
Describe the mechanisms available to regulate blood flow.
Describe how fluid exchange occurs across the capillaries.
What are the basic changes which occur in the cardiovascular system at birth? Describe a few pathologies involving these changes or lack thereof.
The layer of the arteriole wall which provides the properties of contractility and elasticity is the:

a. tunica adventitia
b. tunica intima
c. tunica media
d. tunica externa
e. tunica elastica
The two way exchange of substances between blood and tissue cells occurs ony through:

a. arterioles
b. capillaries
c. venules
d. all arteries
e. veins
Which of the following blood vessels has the lowest blood pressure?

a. capillary
b. venule
c. artery
d. arteriole
e. large veins
If the resistance to flow increased by a factor of three (tripled) to a specific vascular bed, how would the flow to that bad be affected?

a. It would increase by 16
b. It would decrease by 16
c. It would increase by 3
d. It wou
Which of the following diseases of the cardiovascular system is the most common cause of death in the US?

a. Diseases of heart valves
b. Stroke
c. Coronary heart disease
d. Congestive heart failure
e. Congenital heart defec
What is the ejection fraction for a heart which has a stroke volume of 50 ml/beat and an end-diastolic volume of 150 ml?

a. 0.10
b. 3
c. 0.55
d. 0.33
e. 50 ml
Which vessels comprise the microcirculation?

a. venules, capillaries and veins
b. venules, capillaries and arteries
c. capillaries, venules and arterioles
d. capillaries, veins and arteries
e. venules, arterioles and veins
Which of these terms applies to veins?

a. resistance vessels with low pressure
b. capacitance vessels with high velocity
c. contain valves and have high pressure
d. contain 60-70% of total blood volume
e. low pressure and h
What is the total resistance in a parallel circuit if the individual resistances are 2, 3 and 5?

a. approximately 1
b. approximately 2
c. approximately 3
d. exactly 10
If the resistance to a vascular bed doubled, what impact would that change have on blood flow to that area?

a. Flow would increase by 2 times
b. Flow would decrease by 1/2
c. Flow would increases by 16
d. Flow would decrease by
If your heart were stopped for 15 seconds what would be the result:

a. blood pressure in the arterial system would drop to zero
b. blood pressure in the veins would increase to about 7 mm Hg
c. blood pressure in the veins would drop
What comprises the microcirculation?
The arterioles, capillaries and venules comprise the microcirculation.
What is Poiseuille's Equation (also more commonly called the blood flow equation)?
the basic blood-flow equation is critical to determining physical factors which affect blood flow (BF). BF (for an individual organ) or cardiac output (if analyzing the total flow) = BP/R

blood flow = (delta BP x PI x r4) / 8 Lu

r = vessel radius
L = vessel length
u = blood viscosity
delta BP or delta AP = pressure gradient from one portion of the circuit to another
If the resistance to the kidney increased by a factor of two (doubled) what affect would this have on the blood flow to the kidney if the pressure gradient stayed constant?
If the radius of the vessels to the kidney decreased by 1/2, what affect would this have on the blood flow to the kidney if the pressure gradient remained constant?
How would you describe the velocity of blood in the arterial system?
How would you describe the velocity of blood in the venous system?
If the heart were arrested for a short period, what would be the blood pressures for the arterial and venous systems?
If the heart were started up again, how would the blood pressure in the arterial and venous systems change?
What is the equation for stroke volume using EDV and ESV in the equation?
Stroke volume (SV): The volume of blood ejected from the heart per beat

SV = EDV - ESV = 70 ml/beat
If the pulse pressure is 30 mm Hg and the systolic blood pressure is 130 mm Hg. what is the diastolic blood pressure?
What valve opening does the blood cross in traveling from the left atrium to the left
If your arterial blood pressure decreased, what two major variables may have changed? What if the pressure increased?
If an experimental research animal weighed 10 kg, how much plasma volume would that animal have if the hematocrit or packed cell volume is .5?
If a parallel circuit such as we have in the cardiovascular system had two vascular beds with resistances of 1 unit and 2 units respectively, what would be the total resistance through those two circuits?
What are 3 functions of the pericardium?
What is the layer of the pericardium that is next to the fibrous pericardium?
What are two functions of the fibrous skeleton?
This structure which is composed of connective tissue provides:

1. attachment for the
cardiac valves and myocardial tissue. Without this tough structure, the valves would lack support and cardiac muscle would have no basis for developing tension during systole.

2. electrically isolates the atria from the ventricles thereby, requiring a specific pathway (conduction system) for the electrical signal, which originates in pacemaker cells in the right atrium.
When does the majority of the blood flow in the coronary arteries occur?
Where does the coronary artery originate from?
Where does the coronary circulation end?
What cell type of the arterial wall is the first to be injured leading to atherosclerosis?
What are the 4 cell types which are involved in atherosclerosis?
What is the likely cause for the relatively long refractory period of cardiac muscle?
What ionic events exist during the pacemaker potential?
What ionic events exist to cause the rapid depolarization of heart muscle?
What ionic events exist to cause the rapid depolarization of pacemaker cells?
Where is the normal pacemaker for the heart?
What other regions could become pacemakers?
What are the regions and structures encountered as the action potential from the pacemaker travels to the ventricular muscle?
What happens to the electrical signal at the AV node? What might be the purpose?
Provide a discussion of the events of the cardiac cycle beginning at end-diastole and ending with end-diastole. Mention pressure changes for the left heart; valve activity; and volume changes in the ventricle. What are the phases within systole and diast
What causes the heart sounds?
Provide an example of a systolic murmur.
Provide an example of a diastolic murmur.
What do the "P" wave, "QRS" wave or complex, and the "T" waves represent?
Plot a pressure-volume curve for the left ventricle and describe what is occurring on the four portions of the “loop.”
Draw the events of the cardiac cycle and depict whether the semilunar valves are open or closed; likewise for the atrioventricular valves.
Label an ECG and denote what each wave represents.
List the target organs which are affected during the arterial baroreceptor reflex.
Where are the vasomotor centers located?
Where are the arterial baroreceptors located in the baroreceptor reflex?
If your hydrostatic pressure in the capillaries is 40 mm Hg; the osmotic pressure in
the capillaries is 25 mm Hg; the tissue hydrostatic pressure is 1 mm Hg; and the osmotic pressure in the tissues is 2 mm Hg, what is the net filtration pressure? Is
How would the sympathetic nervous system affect the tone of arterioles?
What is the difference between metabolic respiration and ventilation?
Respiration is concerned with breathing, the exchange of gases between air and blood and between blood and tissue fluid and the use of oxygen in cellular metabolism.

Ventilation is concentrated on the process of moving air in and out of the lungs and the process of gas exchange in the lungs.
What are the two major functions of the respiratory system?
The primary function is gas exchange.

The secondary function is to control the pH of the blood. The H+ must be between 7.2 and 7.4.
What are the major divisions of the respiratory system? Which of these are conducting pathways and which are respiratory?
The conducting region of the respiratory system consists of the passages that serve only for airflow - from the nostrils through the bronchioles.

The respiratory division consists of the alveoli and other distal gas exchange regions.
What is the role of smooth muscle and the autonomic nervous system in controlling respiration?
Smooth muscle wraps around the bronchioles. The ANS controls the diameter of the bronchioles by controling the amount of contraction and relaxation in the smooth muscle wrapped around the bronchioles. In the lungs, smooth muscle contraction is under the control of the parasympathetic nervous system and the muscle relaxation is under the control of the sympathetic nervous system.

Asthma results when these muscles contract inappropriately and restrict passage of air through these small tubes.
What is Boyle's law? Explain why Boyle's law is important to the movement of air in and out of the lungs.
Boyle's law = V1P1 = V2P2

This means that gas can be compressed and as the pressure on the gas increases the volume decreases. It follows that as the volume increases, the pressure decreases.

This is important because the respiratory system can be considered a closed container connected to the atmosphere: when volume of air increases pressure in the lungs decreases.
What is the relationship between the difference in pressure and the movement of air?
P = RF


P - is the pressure differential between inside the lungs and the outside world
R - is the resistance to airflow in the lungs
F - is the flow of air

Expanding the volume of the thoracic cavity reduces the pressure in the lungs and permits air to flow into them.
Describe the anatomy of the pleura. How are the pleura arranged with respect to the thoracic body wall and the lungs?
The pleura can be compared to a plastic bag whose inside contains a thin film of water. The surface tension of the water will allow the internal surfaces of the bag to cling to one another. In biology, this bag is formed by a continuous epithelium. The apical regions of this epithelium face the thin film of fluid in the lumen. The outside of the bag is equivalent to the basilar surfaces of the epithelium whos basil lamina is connected mechanically on one side of the bag to the wall of the thoracic cavity, and on the other side to the surface of the lung.
Why is surface tension important to the interpleural space?
The surface tension of the water will allow the internal surfaces of the bag to cling to one another. In biology, this bag is formed by a continuous epithelium. The apical regions of this epithelium face the thin film of fluid in the lumen. The outside of the bag is equivalent to the basilar surfaces of the epithelium whose basil lamina is connected mechanically on one side of the bag to the wall of the thoracic cavity, and on the other side to the surface of the lung.
What is intrapulmonary pressure? What is intrapleural pressure?
The pressure found inside the intrapleural cavity is known as the intrapleural pressure. This pressure is always negative by about 4 mm Hg with respect to the pressure inside the lung and with respect to the atmosphere.

The pressure inside the lung is intrapulmonary pressure and changes from being more negative than the atmosphere (inspiration) to more positive than the atmosphere (expiration).
What is the value of the pressure within the intrapleural space with respect to the intrapulmonary pressure and with respect to atmosphere? How is it maintained and why is it important?
The pressure inside the intrapleural cavity is always negative by about 4 mm Hg with respect to the pressure inside the lung and with respect to the atmosphere.

This pressure is imprtant because if the wall of the pleural cavity is breached and then pressure in the cavity comes to equilibrium with atmospheric pressure, the lung could not be reinflated because a pressure gradient cannot be created. This is called collapsed lung.
How is the volume of the thoracic cavity changed? Describe how the intrapulmonary pressure is made more negative. What is the role of contraction of the diaphragm? How does this result in inspiration?
Increasing the volume of the thoracic cavity is mostly the job of the diaphragm. The diaphragm separates the thoracic and abdominal cavities forming a dome up into the thoracic cavity. When the muscle fibers contract and shorten, the diaphragm flattens, the dome is eliminated and the volume of the thoracic cavity increases. Inspiration largely results from the increase in the volume of the thoracic cavity that results from flattening the diaphragm. Inspiration stops when the diaphragm finishes contracting and the volume of the thoracic cavity comes to a steady state so the intrapulmonary pressure becomes equal to the atmospheric pressure. At this point, air is neither entering (inspiration) or leaving (expiration) the lungs.
Why do the Type II septal cells help make breathing easier?
A subset of epithelial cells in the alveoli called Type II septal cells secrete molecules called surfactants. These are similar to detergent and serve to keep the alveoli from sticking together by helping to reduce surface tension. Phospholipids are an important component of the surfactant.
What is expiration?
Inspiration requires a muscular effort and therefore an expenditure of ATP and calories. By contract, normal expiration during quiet breathing is an energy-saving passive process that requires little muscular contraction other than a braking action.
Why is compliance important in expiration?
The stretchy characteristic of the lung is called compliance; that is the lungs themselves are elastic, largely because of the elastin in the basil lamina and connective tissue that surrounds the epithelia of the aveoli.

Because of compliance, the lung tends to contract into a small volume. Under normal conditions, the lung would contract further if its compliance were not off set by its attachment to the pleura, and the negative pressure in the pleural cavity. When the diaphragm relaxes, it returns to its domed shape and intrudes into the thoracic cavity and reduces the thoracic cavity volume. Equilibrium is reached when the force exerted by compliance of the lung is equal to the force exerted by the lung's attachments to the pleura.
Why is compliance in the lung a problem if the intrapleural pressure is the same as the atmospheric pressure?
If the wall of the pleural cavity is breached and the pressure in the cavity comes to equilibrium with atmospheric pressure, the lung cannot be reinflated because the compliance of the lung allows it to contract and a pressure gradient cannot be created. The lung cannot be reinflated until the breach in the wall of the pleural cavity is sealed, and the pleural cavity is again at a negative pressure with respect to the intrapulmonary pressure.
What is tidal volume? Of this amount, how much enters the respiratory zone with each inspiration?
With each inspiratory cycle during normal quiet breathing, about 500 ml of air enters and leaves the lungs. This volume of air is called the tidal volume.

Of this volume, about 150 ml remains in the conducting airways of the trachea and bronchioles and does not participated in gas exchange; the remaining 350 ml of air enters te aveoli.
How much air remains after expiration and what is it called?
Upon expiration, about 500 ml of air is expired. Of this volume, 150 ml remains in the alveoli and is known as the alveolar dead space.
What are the functions of blood?
- distribution of exygen, transport of waste and transport of hormones

- regulation of body temperature, pH and fluid volume

- protection by preventing blood loss and infection
What are the two major components of blood?
- formed elements:
* red blood cells (45%)
* white blood cells and platelets (1%)

- plasma (55%)
* albumin
* fibrin and proteins involved in clotting
* globulins including immunoglobulins
What does a hematocrit measure?
A hematocrit is a measure of the proportion of the blood volume occupied in cells
What are the formed elements? Of these, which ones are truly cells?
There are three formed elements:

- erythrocytes
- leukocytes
- platelets

Only leukocytes are true cells with a full complement of cell machinery. Mature erythrocytes are anucleate and contain no ER or mitochrondria. Platelets are cell fragments that play a roll in blood clotting
What is the function of each of the formed elements?
- red blood cells are specialized for carrying oxygen and CO2. O2 is carried by red blood cells via hemoglobin

- platelets are cell fragments derived from cells called megakaryocytes which are derived from hemocytoblasts and become very large. Thses cells then fragment into 2-4 um diameter pieces

- white blood cells originate as hemocytoblasts that differentiate into either granulocytes or monocytes important in the immune system
What is the major cytoplasmic protein in red blood cells? What is its function?
Hemoglobin's function is to carry oxygen to the tissues from the lungs and to carry carbon dioxide from the tissues back to the lungs.
What atom in the protein in hemoglobin binds oxygen? Describe how this atom is incorporated into the protein.
Hemoglobin is a molecule constructed of four protein molecules called globins named alpha1, alpha2, beta1, and beta2. Each globin protein is attached to a heme group. Each heme group contains an atom of iron attached to four nitrogens in the center of a porphyrin ring. Because each iron atom binds a molecule of oxygen, each hemoglobin molecule binds four oxygen molecules.
Where would you find oxyhemoglobin and deoxyhemoglobin?
When oxygen is bound to hemoglobin, it is called oxyhemoglobin, and when the oxygen has left the hemoglobin, it is called deoxyhemoglobin.
What is erythropoiesis and where in the body does it occur?
Erythropoiesis is the production of red blood cells and it occurs in the red bone marrow.
Differentiate between hematopoiesis and erythropoiesis. What is the stem cell that is common to both?
Hematopoiesis is the production of formed elements of blood, while erythropoiesis is specific to the production of red blood cells. All formed elements arise as hematopoietic stem cells.
How are mature erythrocytes different from other cells?
In the maturation process, the red blood cell to be loses its nucleus and protein synthesis machinery.
What is the pathway for erythrocyte production, and why are reticulocytes a measure of the rate of erythrocyte production?
Red blood cells begin in the red bone marrow, primarily in the axial skeleton, pelvic girdle, and in the proximal epiphyses of the humerous and femur as hemocytoblasts.

In response to a series of hormones and receptors on the cell surface, the hemocytoblast is destined to become a red blood cell. In erythrocytes, hemocytoblasts pass through a myeloid precursor cell stage before becoming a proerythroblast. As a normoblast, the cell expels its necleus and proceeds to the reticulocyte stage. Reticulocytes retain some of the ER and ribosomes that were used to make the hemoglobin and other erythrocyte proteins. These organelles soon fade and fully differentiated erythrocytes contain no ribosomes or ER.

The presence of large numbers of reticulocytes in blood indicates that there has been a recent increase in blood cell production since these cells are the youngest erythrocytes in the circulation and they retain remnants of the ER for only a few days after entering the blood stream from the red bone marrow where they are produced.
Describe the feedback system that controls erythrocyte production including the molecules that control the feedback and the sites of production and action for these molecules.
The production of erythrocytes is controlled over a period of days by the synthesis and secretion of erythropoietin into the circulation. When the level of oxygen reaching the kidney drops, the kidney cells are stimulated by this anoxia to produce erythropoietin and secrete it into the blood. In the red bone marrow of spongy bone, erythropoietin enhances the production of erythrocytes. The increased number of erythrocytes produced improves oxygen-carrying capacity of the blood and causes the kidney to decrease erythropoietin production. As erythropoietin levels decline with increasing oxygen levels, erythrocyte production declines.
Why do erythrocytes have a limited life span? How are they disposed of when worn out, and how are their constituents recycled?
Because erythrocytes lack protein synthesis mechinery, they have a limited life span that averages about 90-120 days. Geriatric erythrocytes are engulfed and digested by macrophages in the spleen, liver and red bone marrow. The macrophages begin the recycling process with the hemoglobin. The amino acids from the globin chains are released back into the circulation to be used again in other proteins. The iron molecules that have been removed from the heme portion of the hemoglobin molecule are stored in the liver as ferratin or hemosiderin. The porphyrin ring is converted to bilirubin in the liver and excreted into the small intestine. Bacterial enzymes in the intestines convert most of the bilirubin to stercobilin which gives feces its brown color. A portion of the bilirubin is converted in the intestine and liver, reabsorbed into the blood and excreted through the kidneys; urine gets its yellow color from the waste product of hemoglobin destruction. The kidneys can excrete bilirubin only after it has been modified in the liver and intestines. The iron is released from the liver and reused in the red bone marrow as transferrin.
How are platelets different from other formed elements? Why are they important?
Platelets are cell fragments that are essential for blood clotting. As with other formed elements in blood, platelets originate as hemocytoblasts in the red bone marrow, become myeloid stem cells and proceed through promegakaryoblasts to megakaryocytes. The megakaryocytes are extremely large, multinucleate cells that fracture into platelets. Platelet formation occurs when the plasma membrane of the megakaryocyte invaginates and divides the cytoplasm into vesicle-containing compartments. The cells then fragment to form thousands of membrane-bound compartments called platelets. The production of megakaryocytes is controlled by a molecule called thrombopoietin.
What is the role of hemostasis in homeostasis? What are the three phases of hemostasis, and what occurs in each phase?
Hemostatis is the process of halting the loss of blood. The three phases are:

1. vascular spasms - when arterioles or arteries are damaged, the damage causes the smooth muscle to contract narrowing the diameter of the vessel reducing the flow of blood.

2. plug formation - the role of platelets is to plug the break in the vessel. the initial event is to plug the hole. because the vessel is surrounded by loose connective tissue, there is an abundance of collagen exposed by the break in the vessel.

3. coagulation - platelets interact with collagen and stick; they also become sticky so that they stick to one another. ONce stuck, vesicles in the platelets begin to fuse with platelet plasma membrane and release material into the extracellular space that promotes coagulation.
In the process of coagulation, what are the five steps between breaching the blood vessel to blood clot formation?
1. As the plug is forming, platelet factor 3 (PF3) and tissue factor released from damaged cells combine with calcium and other clotting factors to promote blood-clot formation.

2. The combination of PF3, calcium and other factors activates prothrombin activator.

3. This molecule converts prothrombin to thrombin.

4. Thrombin converts:

5. Fibrinogen, which is soluble in the blood to fibrin which is an insoluble filament-like molecule. The fibrin molecules intertwine, capture eyrthocytes and form a clot.
What are the components of the lymph system?
The lymph system consists of a dispersed system of vessels called lymphatic vessels and a series of lymphoid tissues that include the lymph nodes, tonsils, spleen and thymus.
What is lymph and how is it related to the blood?
The lymph is primarily fluid that has escaped from the blood into the tissues. It contains proteins.
What is the role of the lymph vessel?
The lymph vessels provide a series of drainage canals that return the lymph to the blood.
How is the entrance of lymph into the lymph vessels controlled? How is lymph moved through the lymph vessels?
The hydrostatic pressures on blood force some of the fluid out into tissue spaces. Some of this fluid returns to capillaries and some of it passes into the lymph capillaries. The lymph capillaries are lined with endotheilial cells and entrance of fluid from the tissue spaces is regulated by a set of flap-like valves in the lymph vessels. One end of the flap is anchored to the tissue by filaments while the other end is free to respond to increased fluid pressure in the tissue space. If the pressure is higher in the tissue space than in the lymph capillary, fluid moves from the tissue space into the lymph capillary. If however, pressure is higher in the lymph capillary, the valve shuts from the internal pressure and prevents backflow. In this way, lymph flows from the tissues into the lymphatic collecting vessels.

Lymph collected into the lymphatic collecting vessels passes from the ducts into the lymph nodes.
How are the lymph nodes associated with the lymph vessels?
Lymph in the lymphatic vessels passes through the lymph nodes. These structures act as filters in the lymphatic system. Afferent vessels deliver lymph to the node; efferent vessels carry lymph away. The afferent vessels enter the node on the convex side and the efferent vessels exit the node on the concave side.

The lymph percolates through the medullary sinuses within the node and as it does so, it contacts a variety of immune cells. If the lymph contains bacteria, viruses, fungi or other foreign proteins, immune cells in the lymph nodes recognize the invaders and act to destroy them.

The germinal center is the site where the B lymphocytes reside. These cells can be induced to divide in response to contact with foreign proteins from invading organisms. Macrophages and lymphocytes are found attached to reticular fibers constructed from reticulin, a filamentous protein secreted by fibroblast-like cells in the lymph nodes.
What are the germinal regions in lymph nodes? What cells are located here and why are they important? Why is the flow of lymph through the lymph nodes important?
The germinal center is the site where B lymphocytes reside. These cells can be induced to divide in response to contact with foreign proteins from invading organisms. Macrophages and lymphocytes are found attached to reticular fibers constructed by reticulin.

Lymph nodes act as filters in the lymphatic system.
What are the two main roles of the spleen? Where in the spleen are these roles carried out?
The spleen is the erythrocyte graveyard where old erythrocytes are consumed by macrophages and the process of salvaging and recycling the heme begins. The site of erythrocyte disposal, which is enriched for macrophages in the spleen is the red pulp. Separate regions in the spleen are enriched for B lymphocytes and constitute germinal centers; these regions are called the white pulp. As an organ of the immune system, the spleen and its regions of white pulp are important for combating infections in the blood. The spleen is an important lymphoid tissue where the blood is exposed to the immune system.
What are the tonsils and Peyer's patches? Where are they found? Why are these locations strategic?
Tonsils, which are located in the pharynx, are strategically positioned to contact bacteria, fungi and viruses that may enter the body through the nose and mouth.

The Peyer's patches are lymphoid tissue similar to tonsils that are located in the intestines. Peyer's patches are also called Gut associated lymphoid tissue (GALT).

The Peyer's patches and tonsils have numerous germinal centers where they wait to encounter novel, foreign proteins that belong to invading organisms.
What is the thymus? What cells mature in the thymus? How is the thymus structurally different from other lymphoid tissues?
The thymus is a highly specialized lymphoid tissue that supports the maturation of T lymphocytes after they have left the red bone marrow and migrated through the circulartory system to the thymus.

Once in the thumus, the prolymphocytes reside on specialized epithelial cells that "nurse" the immature T lymphocytes to immunocompetence.

Selection of T cells in the thymus is very important for normal immune system function. T cells may be retinaed and exported to the blood system (positive selection) or discarded (negative selection). Negative selection may occur either because it fails to respond to the MHC proteins carried on other thymus cells or because it responds too strongly to the MHC proteins and the protein fragments they carry. In the first case, the T cells are permitted to die before leaving the thymus because they will be ineffective in recognizing cells that express foreign proteins. In the second case, the T cells are allowed to die before leaving because they bind too tightly to the MHC complex and "self" proteins.
What is a major functional difference between lymph nodes and other lymph tissues?
Only the lymph nodes contain lymph; the other lymphoid tissues have no flow of lymph through them.

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