The Circulatory System

Question 1

Why the circulatory system ? I mean come on, do we really need it ….

Answer 1

Every cell of the human body must be supplied with oxygen and nutrients and must rid itself of waste. These requirements are met by a circulatory system that transports these materials between cells and their surrounding environment.

If we didn’t have the circulatory system, our cells would not be able to receive needed materials that allow it to make proteins and create ATP.

Question 2

The cardiovascular system contains

Answer 2

a muscular heart and the vessels that transport the blood : arteries, veins and capillaries.

Question 3

Functions of the circulatory system

Answer 3

The functions of the circulatory system include:

(1) transporting gases, nutrients, and wastes throughout the body, but also
(2) clotting to prevent loss of blood from ruptured vessels
(3) fighting invasion of the body by foreign bodies.

Question 4

Arteries - what about ‘em?

Answer 4

They carry blood away from the heart. elastic, thick-walled vessels which are capable of expanding to accommodate the larger blood volume flowing from the heart at the end of each heartbeat. Large arteries actually expand and recoil to help the heart pump blood through the systemic circulation. Small arteries called arterioles are constricted and dilated by muscles controlled by the sympathetic and parasympathetic nervous system which increases or decreases the blood pressure, respectively. This mechanism prevents you from fainting when you get out of bed each morning. Arterioles are the vessels primarily responsible for providing differing levels of “peripheral resistance” to blood flow (caused by varying blood pressure) depending on the conditions affecting the body.

Question 5

Talk about capillaries ……….

Answer 5

The branching of arterioles causes formation of even narrower tubes called capillaries which are interconnected to form capillary beds which perform the exchange of materials with the cells of the body. The blood is collected from the capillary beds by small veins called venules many of which join to form a vein which returns the blood to the heart.

Question 6

What do veins do ?

Answer 6

Veins carry blood back to the heart.… Veins are thinner-walled vessels which are under less pressure from the heart. For this reason veins do not have “pulses”. Only arteries, especially the ones close to the heart, should have palpable pulses. Veins have internal valves which open toward the heart and close at the end of a heart beat to prevent blood from flowing backward as the blood is returned to the heart. Because of their compliance (stretch with little recoil), the largest amount of blood in the cardiovascular system is contained in the veins.

Question 7

What are the two circuits of the heart ? Which side of the heart runs each

Answer 7

Pulmonary Circuit - run by the right side of the heart. Pulmonary arteries will carry blood to the lungs where it will pick up oxygen. Pulmonary veins wil bring oxygenated blood back to the heart

Systemic Circuit- run by the left side of the heart. After the blood is returned to the heart from the lungs, the left side of the heart works to pump the blood out to the body

Question 8

The heart is located in what area of the thoracic cavity ?

Answer 8

the mediastinum.( or mediastinal cavity ) between the lungs. At approx level of t5-T6 vertebrae and found between the second rib and the sixth and fith rib

1/3 of the heart will be found to the right of the median plane and 2/3 to the left
Heart is fist sized cone shaped muscular organ and about 10 oz

Question 9

What is the layer of the heart that contracts?

Answer 9

The bulk of the heart, called the myocardium, is composed mainly of cardiac muscle and is the layer that actually contracts. The myocardium muscle fibers are highly branched and are attached by collagen connective tissue fibers which link all parts of the heart together.

Question 10

What is the name of the tough, thick sac which the heart is enclosed in and anchors it to the diaphragm?

Answer 10

the pericardium

Question 11

What are the layers of the pericardium ?

Answer 11

The inner (epicardium) and outer layers of the pericardium are covered by a smooth layer of endothelium. A special lubricating fluid between the layers allows the heart to slide around with very little friction.

The epicardium is the inner layer of the pericardium. It is also the outermost portion of the tissues that make up the “heart wall”

Question 12

What makes up the heart wall?

Answer 12

The heart wall is made of 3 layers: epicardium, myocardium and endocardium. The thickness of the heart wall varies in different parts of the heart.

Epicardium. The epicardium is the outermost layer of the heart wall and is just another name for the visceral layer of the pericardium. Thus, the epicardium is a thin layer of serous membrane that helps to lubricate and protect the outside of the heart. Below the epicardium is the second, thicker layer of the heart wall: the myocardium.

Myocardium. The myocardium is the muscular middle layer of the heart wall that contains the cardiac muscle tissue. Myocardium makes up the majority of the thickness and mass of the heart wall and is the part of the heart responsible for pumping blood. Below the myocardium is the thin endocardium layer.

Endocardium. Endocardium is the simple squamous endothelium layer that lines the inside of the heart. The endocardium is very smooth and is responsible for keeping blood from sticking to the inside of the heart and forming potentially deadly blood clots.

Question 13

What structure separates the chambers into a right and left set?

Answer 13

The septum

Question 14

What chambers receive blood and which chambers pump the blood ?

Answer 14

The two upper receiving chambers are called the atria; the two lower pumping (sending) chambers are called the ventricles. The atria are smaller than and not as muscular as the ventricles which must force the blood through vessels to distant parts of the body.

Question 15

What are the auricles and what is the signicance of the fossa ovalis?

Answer 15

The atria each have a muscular pouch on the upper surface called the auricles. There is also a shallow depression on the septum separating the atria. This depression, called the fossa ovalis, marks the place of an opening between the atria which is present in all developing fetuses. It allows fetal blood to move directly from right to left atrium, bypassing he undeveloped lungs

Question 16

What are the four valves that control blood flow ?

Answer 16

The tricuspid valve controls blood flow between the right atrium and the right ventricle.

The bicuspid (mitral) valve connnects the left atrium to the left ventricle

The pulmonary semilunar valve controls blood flow between the right ventricle to and the lungs

The aortic semilunar valve controls blood flow between the left ventricle and the aorta.

Question 17

Pathway of blood through the heart

Answer 17

Blood follows a path which can best be described as it returns (in a deoxygenated form) from the cells of the body entering the heart into the right atrium by way of veins called the inferior and superior vena cavae. From the right atrium blood flows through the tricuspid valve into the right ventricle which pumps the blood through the pulmonary valve into the pulmonary arteries to the lungs. After the blood is oxygenated in the capillary bed of the lungs (also losing its carbon dioxide), it is carried by the pulmonary veins to the heart entering the left atrium. This oxygenated blood flows through the bicuspid valve (mitral valve) into the left ventricle which pumps it through the aortic valve into the aorta (the largest vessel in the body) which carries it to capillary beds of the systemic trunk, supplying the cells of all body tissue with oxygen and nutrients. Deoxygenated blood is then returned to the right atrium through the vena cavae which completes the circuit.

Question 18

What supplies the heart with its own blood supply?

Answer 18

The left and right coronary arteries, which arise from the base of the aorta and supply oxygen and nutrients to the heart tissues.

The left coronary artery runs toward the left side of the heart and divides into the anterior interventricular artery and the circumflex artery which supply the left atrium and the left ventricle.

The right coronary artery runs toward the right side of the heart and divides into the posterior interventricular artery and the marginal artery which supply the right atrium and the right ventricle.

Question 19

Track the flow of blood through the heart

Answer 19

1. Deoxygenated blood flows toward the heart via the cranial and caudal vena cava (inferior and superior).
2. Blood passes through the right AV valve (tricuspid)
3. Blood travels into the right ventricle
4. Blood passes through the pulmonary semilunar valve
5. From here it is pumped into the lungs’ circulation via the pulmonary artery.
6. Blood picks up oxygen in the lungs.
7. The oxygenated blood travels through the pulmonary veins to the left atrium.
8. Blood passes through the left AV valve (mitral/bicuspid) and enters the left ventricle.
9. The blood passes through the aortic semi-lunar valve
10. Blood then enters the aorta where it travels into systemic circulation (to deliver oxygen and nutrients to tissues)

Question 20

What is the cardiac cycle and what does it consist of ?

Answer 20

Consists of contractions and relaxation of the heart muscle. The term systole refers to contraction of heart chambers and the word diastole refers to relaxation of these chambers.

The heart contracts, or beats, about seventy times a minute, and each heartbeat lasts about 0.85 seconds

Each heartbeat is a cardiac cycle

Question 21

What are the phases of the cardiac cycle?

Answer 21

Each heartbeat, or cardiac cycle, consists of the following phases:

(1) the atria contract for about 0.15 second (while the ventricles relax),
(2) the ventricles contract for about 0.30 second (while the atria relax),
(3) all chambers relax for about 0.40 second.

The short systole of the atria is understandable since the atria send blood only into the ventricles, but the ventricles pump blood into the much larger systemic or pulmonary circulatory circuits.

The contraction of the heart is intrinsic, meaning that the heart will beat independent of any nervous stimulation, but it is regulated by the nervous system which can increase or decrease the heartbeat rate.

Question 22

What is systolic pressure?

Answer 22

Systolic pressure results from blood being forced into the arteries during ventricular systole (contraction)

Question 23

What is diastolic pressure ?

Answer 23

the pressure in the arteries during ventricular diastole (relaxation)

Question 24

What device measures blood pressure ?

Answer 24

a sphygmomanometer, which has a pressure cuff that measures the amount of pressure required to stop the flow of blood through an artery.

Question 25

Blood pressure is stated in

Answer 25

millimeters of mercury. A blood pressure reading contains 2 numbers, for example, 120/80—which represents systolic and diastolic pressures, respectively.

120/80

S/D

Question 26

What happens as blood flows from the aorta into the various arteries and arterioles ?

Answer 26

blood pressure falls. Also, the difference in pressure between systolic and diastolic gradually diminishes

Question 27

Compare the flow of blood in the capillaries with the flow of blood in the veins and the arteries

Answer 27

In the capillaries, there is a slow, fairly even, flow of blood. Blood pressure in the veins, however, is low and can even approach zero. Arteries have the highest blood pressure because blood is actively being pumped into them by the heart

Question 28

If veins have such low blood pressure, how are they able to return blood to the heart?

Answer 28

1) low resistance in the venous walls,
2) the presence of internal valves which prevent the backward flow of blood
3) the assistance of muscular movement in the limbs and chest, blood in the veins is able to maintain a flow rate significant enough to return the blood to the heart.

Question 29

Answer 29

For the heart to function as a pump, it must contract and relax in a cyclical pattern.

The cycle is divided into two parts:

• *Systole**: the heart is contracting and ejecting blood into circulation
• *Diastole:** the heart is relaxing and filling with blood.

The cardiac cycle is the sequence of events in ONE complete heart beat.

1. Ventricular contraction (systole) causes a rise in ventricular pressure and results in the closure of the AV valve (LUB) and opening of the aortic and semilunar valves.
2. During ventricular relaxation (diastole), the AV valves open and the aortic semilunar valves close (DUB) due to back pressure in the aorta and pulmonary trunk.

First heart sound is the closure of the AV valves. (Tricuspid and Bicuspid (mitral))
Second Heart sound is the closure of the semilunar valves. (Pulmonary and aortic)

Question 30

What maintains the heart’s intrinsic rhythmic abilities ? Could it beat on its own?

The action of the nervous system enables the heart to respond to changes in:

Answer 30

an elaborate electrical system.

The contractions of the cardiac muscle begin within the heart muscle itself, making it somewhat independent of any nerve supply from the central nervous system. If removed from the body, the heart could continue to beat on its own with proper nutrients and oxygen. However, the nervous system and endocrine systems do regulate the heart rate through neurotransmitters such as norepinephrine and acetycholine. This enables the heart to respond to variations in blood pressure and emotional and physical stressors. The following is a brief description of the electrical impulse that moves through the heart during each cardiac cycle.

Question 31

Where does the electriclal impulse of the heart begin ? What structure is known as the pacemaker of the heart?

Answer 31

The electrical impulse begins at the SA node (sinoatrial node) found in the right atrium (1). The SA node is known as the “pacemaker” of the heart and is a small mass of specialized cardiac muscle.

Question 32

Track the transmission of the hearts electricla impulse

Answer 32

(1). The SA node is known as the “pacemaker” of the heart and is a small mass of specialized cardiac muscle. The impulse spreads through the atria creating atrial systole. The impulse then travels through the AV node (2) into the bundle of His. From there, the impulse continues to travel towards the ventricular apex (downward point of the heart). Finally, it travels through the Purkinje fibers to the myocardium.

Question 33

What is this called ?

Answer 33

An ECG. It measures electrical impulses in the heart.

Question 34

What do each of the lettered waves represent?

Answer 34

Different parts of the ECG tracing represent different electrical and corresponding mechanical events in the heart. Medical personal commonly use ECGs to monitor and diagnosis patients.

Atrial depolarization (active firing of a nerve impulse) and atrial systole are denoted as the P-wave. Ventricular depolarization and ventricular systole are denoted as the QRS complex. Ventricular repolarization (returning to rest) and ventricular diastole are denoted as a T-wave. There is no way to note the repolarization of the atria. Its activity is lost within the QRS complex.

Question 35

What happens when someone tends to stand still for a long time such as a store clerk standing a a cash register ?

Answer 35

Blood tends to pool in the veins. Once the veins are fully distended, they can accept no more blood from the capillaries. Pressure in the capillaries increases and large amounts of plasma are forced out of the thin capillary walls. Once arterial blood pressure drops, blood flow to the brain is reduced and fainting can result. Lying (or falling) in a prone position is a protective response, as it increases blood supply to the brain.

Question 36

Heart failure and edema effects

Answer 36

Heart failure can cause an abnormal backup of fluids in the body leading to edema and high blood pressure. Left-sided heart failure tends to cause pulmonary edema, or a back up of fluid in the lungs known as congestive heart failure. Right-sided heart disease tends to cause peripheral edema or a back up of fluids in the body/limbs.

Question 37

What is hypertension?

Answer 37

defined as the condition when the systolic and diastolic pressures are significantly higher than 120/80 mm Hg.

Hypertension is seen in individuals with kidney disease and also in individuals who have atherosclerosis, which is an accumulation of soft masses of fatty materials, particularly cholesterol, beneath the inner linings of arteries. Such deposits are called plaque, and as it develops, it tends to protrude into the vessel, interfering with blood flow. Plaque can cause a blood clot to form on the irregular arterial wall. As long as the blood clot remains stationary, it is called a thrombus, but if it dislodges and moves along with blood it is an embolus.

If a thromboembolism lodges in a vessel supplying a vital organ of the body like the brain, heart, or lungs, serious complications or sudden death may occur.

Question 38

When does a stroke occur?

When does a heart attack occur?

Answer 38

A stroke occurs when a portion of the brain dies due to lack of oxygen. A heart attack occurs when a portion of the heart muscle dies due to lack of oxygen.

A stroke that results in paralysis or death often occurs when a small arteriole bursts or is blocked by an embolus.

If the coronary artery is partially locked due to plaque, the individual may suffer from pain called angina pectoris, characterized by a radiating pain in the left arm. When a coronary artery is completely blocked, perhaps because of a thromboembolism, a heart attack occurs.

Question 39

What is streptokinase (normally produced by bacteria) and t-PA (tissue plasminogen activator)?

How does aspirin help to lower the probability of a blood clot forming?

Answer 39

Drugs that treat thromboembolism by dissolving a blood clot by converting a molecule found in blood, plasminogen, into the plasmin, an enzyme that dissolves blood clots.

Aspirin is an anti coagulent drug that reduces the stickiness of platelets and thereby lowers the probability that a clot will form.

If a person has symptoms of angina or a thrombolytic stroke, then an anticoagulant drug such as aspirin may be given.

Question 40

What is angioplasty and coronary bypass surgery?

Answer 40

These are surgical procedures that can clear clogged arteries?

In angioplasty, a cardiologist threads a plastic tube into an artery of an arm or a leg and guides it through a major blood vessel toward the heart. When the tube reaches the region clogged by plaque in a coronary artery, the balloon attached to the end of the tube is inflated, forcing the vessel open.

Another alternative is coronary artery bypass surgery. During this operation, surgeons take a segment of another blood vessel from the patient’s body and stitch one end of the aorta and the other end to a coronary artery past the point of obstruction.

Once the heart is exposed, some physicians may also use lasers to open clogged coronary vessels.

Question 41

What are the two main portions of blood ?

Answer 41

the liquid portion, called plasma,

and the “cells” or formed elements consisting of red and white cells and platelets.

Question 42

What is the difference between plasma and serum?

Answer 42

In serum, the clotting proteins have been removed.

In plasma, the clotting proteins are present.

This is accomplished by letting blood sit in a tube until it clots and then centrifuging the sample to separate the solid and liquid portions of the blood. Serum is often used in many laboratory tests

Question 43

What are the functions of plasma?

Answer 43

1) buffers the blood, keeping the pH near 7.4,
2) maintains the blood’s osmotic pressure so that water has an automatic tendency to enter blood capillaries
3) assists in transporting large organic molecules in blood
4) aids in blood clotting.

Question 44

Red blood cells contain which vital protein?

Answer 44

Hemoglobin, which combines with oxygen to carry it in the blood

Question 45

White blood cells are also known as _________

Answer 45

leukocytes

Question 46

What do white blood cells do ?

Answer 46

They are the fighters, the warriors that destroy and capitulate foreign invaders harmful to the body. They can squeeze through the capillary wall and enter the tissue fluid, where they engage bacterial and viral forces of darkness.

Question 47

What do platelets do ? Are they “true” cells?

Answer 47

Platelets are involved in the process of blood clotting. As the platelets “clump” at the site injury, they activate the formation of fibrin threads, which intertwined, with red blood cells, form the framework for the clot.

Platelets are not true “cells”, but fragments of a large bone marrow predecessor called a megakaryocyte

Question 48

What are erythrocytes ?

How many of them are there in a mm of blood?

Answer 48

Also known as red blood cells….. they are small biconcave (curves inward on both sides) disks. Erythrocytes are the most abundant cell in the blood.

There are 4 million to 6 million red blood cells per mm of whole blood, and each one of these cells contains about 250 million hemoglobin molecules.

Question 49

How does hemoglobin carry oxygen ?

What is anemia ?

Answer 49

Hemoglobin contains an iron which combines loosely with oxygen

Anemia results if there are not enough red blood cells or if the red blood cells do not have enough hemoglobin.

The sufferer has a tired, run down feeling

Question 50

What is the origin of red blood cells ? Where are they manufactured ?

How does the destruction of red blood cells engage in recycling?

Answer 50

Red blood cells are manufactured continuously in the red bone marrow of the skull, the ribs, the vertebrae, and the ends of the long bones. Before they are released from the bone marrow into blood, red blood cells lose their nucleus and synthesize hemoglobin. After living about 120 days, they are destroyed chiefly in the liver and the spleen. When red blood cells are destroyed, hemoglobin is released. The iron is recovered and is returned to the red bone marrow for reuse. The heme portions of the molecules undergo chemical degradation and are excreted by the liver as bile pigments.

Question 51

How do leukocytes differ from erythrocytes

Answer 51

White blood cells differ from red blood cells in that they are larger, have a relatively large nucleus and lack hemoglobin (so they don’t carry oxygen)

Question 52

What is an inflammatory reaction ?

Why should pus be saluted ?

Answer 52

When microorganisms enter the body due to an injury, the response is called an inflammatory reaction because there is swelling and reddening at the injured site. This is due to an increase in blood flow to the injured site that helps to delivery these immune cells. The white blood cells can squeeze through the capillary wall and enter the tissue fluid, where they destroy foreign material.

The thick, yellowish fluid called pus contains a large proportion of dead white blood cells that have fought the infection.

Question 53

What are two groups of white blood cells ?

Answer 53

granulocytes and agranulocytes. Granulocytes have granules in there cytoplasm while agranulocytes do not.

Question 54

WHo are teh granulocytes ?

Answer 54

Granulocytes include; neutrophils, eosinophils, and basophils.

Question 55

Describe the fighting action of neutrophils

Answer 55

Neutrophils are the most abundant white blood cell and is responsible for fighting infections, especially those that involve bacteria. Neutrophils use phagocytosis or the ingestion of foreign materials to destroy invaders. Neutrophils have a multilobed nucleus and (when stained) light pink granules in there cytoplasm.

Question 56

What kind of situations do eisinophils primarily respond to?

Answer 56

Eosinophils respond to allergic reactions and parasitic infections.

They are similar in appearance to neutrophils, except that their granules stain a darker/pink to red and are less commonly seen.

Question 57

Who are the rarest of the granulocytes ?

Answer 57

Basophils

They are involved in the release of histamines, a vasodilator, within tissues. Basophils have similar morphology to neutrophils and eosinophils but the granules stain dark blue/purple.

Question 58

What are the two types of agranulocytes ?

Answer 58

lymphocytes and monocytes

Question 59

What are the different kind of lymphocytes ?

Answer 59

B cells , T cells, Natural Killer Cells, plasma cells

functions may include making antibodies, attacking foreign cells or destroying body cells that have lost normal function

Lymphocyte size can vary but lymphocytes are larger than red blood cells but generally smaller than other white blood cells. They have a large dark nucleus with little cytoplasm.

Question 60

Describe monocytes; what are they called once they move into the nucleus

Answer 60

Monocytes are large white blood cells with a “U” or kidney bean shaped nucleus.

Monocytes can move into the tissue where they are then called macrophages. Monocytes and macrophages are the greatest phagocytes of all the blood cells.

Question 61

What parts of the blood are involved in blood clotting or also known as _______?

Answer 61

Coagulation

The “formed elements “ portion of blood specifically platelets.

Also necessary to the process are fibrinogen and prothrombin, which are proteins manufactured by the liver and are free floating in the blood.

Question 62

Describe the blood clotting process

Answer 62

When a blood vessel in the body is damaged, platelets clump at the site of the puncture and partially seal the leak. The platelets and the injured tissues release a clotting factor called prothrombin activator that converts prothrombin to thrombin. This reaction requires calcium ions (Ca+2) to occur. Thrombin, in turn, acts as an enzyme that severs two short amino acid chains from each fibrinogen molecule. These activated fragments then join end to end, forming long threads of fibrin. Fibrin threads wind around the platelet plug in the damaged area of the blood vessel and provide the framework for the clot. Red blood cells also are trapped within the fibrin threads; these cells make a clot appear red. A fibrin clot is present only temporarily. As soon as blood vessel repair is initiated, an enzyme called plasmin destroys the fibrin network and restores the fluidity of plasma. Malfunctions or deficiencies in this clotting cascade can lead to a variety of vascular diseases.

Question 63

What are these ?

Answer 63

Red blood cells

Question 64

Answer 64

Neutrophil

Question 65

Answer 65

Three Eisophils

Question 66

Answer 66

Basophil

Question 67

Answer 67

Two Megakarocytes

Question 68

Answer 68

Platelets

Question 69

Answer 69

Monocyte

Question 70

Answer 70

Lymphocyte

Question 71

What does the lymphatic system consist of ?

Answer 71

lymphatic vessels and the lymphoid organs

This system, which is closely associated with the cardiovascular system, has three main functions:

(1) lymphatic vessels take up excess tissue fluid and return it to the bloodstream;
(2) lymphatic capillaries absorb fats and transport them to the bloodstream;
(3) the lymphatic system helps to defend the body against disease.

Question 72

Answer 72

The lymphatic system consists of lymphatic vessels and lymphoid organs

Question 73

What us the purpose of lymphatic vessels ?

Answer 73

Lymphatic vessels extend to most sections of the body. Larger lymph vessels have check valves, like cardiovascular veins, which prevent the backward flow of lymph, the movement of which is caused by the squeezing action of skeletal muscles.

Question 74

What is lymph ?

Answer 74

excess tissue fluid which enters the lymphatic capillaries

Question 75

Track the flow one way flow of lymph from the lymphatic capillary system to the subclavian veins

Answer 75

The lymph capillaries take up plasma fluid which, under great pressure, has been forced out of the capillaries of the circulatory system and has not been reabsorbed. This fluid bathes the cells assisting the capillaries in delivering glucose, oxygen, salts, amino acids and other nutrients. An accumulation of too much fluid in tissues can cause localized swelling called edema. This excess tissue fluid which enters the lymphatic capillaries is now called lymph and flows from the lymphatic capillaries into larger lymphatic vessels that merge before entering either the thoracic duct or the right lymphatic duct, both located in the shoulder region of the human body. The larger thoracic duct drains the lower extremities, the abdomen, the left arm, and the left side of both the head and the neck. The smaller right lymphatic duct drains the right arm, the right side of both the head and the neck, and the right thoracic area. Lymph then flows from the thoracic duct into the left subclavian cardiovascular vein or from the right lymphatic duct into the right subclavian cardiovascular vein.

Question 76

What are the lymphoid organs?

Where are lymph nodes found and how many are there?

Answer 76

These are major immune system organs that include the lymph noes, the spleen and the thymus gland.

The body has hundreds of lymph nodes which are found at junctions of lymphatic vessels. A lymph node

Question 77

Describe a lymph node

Answer 77

A lymph node is encapsulated in a fibrous connective tissue with many incoming and fewer outgoing lymphatic vessels.

The interior of the lymph node is divided into open spaces called nodules, containing lymphocytes and macrophages which rid the flowing lymph of infectious organisms and other debris. Lymph nodes are grouped together in certain regions of the body, particularly the groin and the armpits.

Question 78

What is the function of the spleen?

Answer 78

The spleen, located in the upper left abdomen, functions to extract old or defective blood cells and platelets, removes debris, foreign matter, bacteria, viruses and toxins from the blood that flows through it.

The spleen is encapsulated in a thin, fragile fibrous connective tissue with an incoming splenic artery and an outgoing splenic vein. The interior of the spleen is divided into open spaces called lobules, containing lymphocytes (located in areas called white pulp) and macrophages (located in blood-rich areas called red pulp) which carry out the functions of the spleen.

Question 79

What is the function of the thymus gland ?

Answer 79

The thymus gland, located in the lower neck, secretes thymosin and thymopeietin hormones which enable the T lymphocytes to mature and function as part of the immunity system.

T cells attack body cells which are foreign, cancerous or infected with pathogens.

The thymus is prominent in newborns, becoming larger during childhood (when it is most active), but growth stops during adolescence and the gland withers away to a mass of fibrous-fatty tissue by old age.

Question 80

What do the tonsils do ?

Answer 80

The tonsils are a group of small lymphoid organs surrounding the throat which gather and destroy bacteria in inhaled air or food.

The lymphoid tissue of the tonsils is invaginated by channels called crypts which trap bacteria and foreign matter. The bacteria then work their way into the lymphoid tissue where most are destroyed

Question 81

What does the immune response involve?

Answer 81

An immune response can be specific or nonspecific. It involves identifying foreign, invading particles and eliminating them.

Question 82

What is a nonspecific immune response ?

Answer 82

Its like natural defenses that are always there; the armies are not brought out.

Nonspecific immune responses prevent pathogens from entering the body and rapidly destroy any that do breach the surface. The skin is part of the nonspecific immune response system. Very few pathogens can penetrate the intact human skin. In addition, sweating actually produces an environment on which only “healthy” bacteria can grow. These beneficial bacteria produce lactic acid which inhibits pathogenic bacteria. Microorganisms entering the stomach are often destroyed by stomach acids and secretions, and those entering the respiratory system are often trapped by mucus.

Question 83

What are cytokines, interferons and interleukins ?

Answer 83

Within the blood circulate many cytokines, which are a large group of peptides and proteins that include interferons and interleukins.

Interferons inhibit viral replication and activate natural killer cells (NK), a lymphocyte. NK cells originate in the bone marrow and are highly effective against tumor cells. Psychological stressors are thought to decrease NK cell activity which can enhance the growth of tumors.

Interleukins, during infection, can reset the body’s thermostat in the hypothalamus to create a fever. Fever helps the body fight infection by interfering with the growth and replication of some pathogens. Fever also causes lysosomes to break down. The lysosomes release digestive enzymes that can destroy a cell infected by a virus. In addition, fever can promote the activity of certain white blood cells. Low fevers of fairly short duration can be necessary for recovery.

Both types of cytokines can be produced by macrophages, which also use phagocytosis to engulf foreign invaders such as bacteria or damaged cells.

Question 84

Are non specific or specific immune responses quicker to activate ?

Answer 84

Nonspecific immune responses act fairly quickly. Specific immune responses take several days to activate but are extremely effective.

Question 85

What are the main lymphocytes involved in specific immune responses?

Answer 85

T cells and the B cells.

Question 86

Describe the action of B cells

Answer 86

Each B cell is genetically programmed to produce a glycoprotein receptor as part of its cell coat. That receptor binds with a specific type of antigen. An antigen is any molecule which can be specifically recognized as foreign by the immune system. B cells are activated when an antigen binds with its receptor. Once activated, the B cell begins to rapidly divide. Each of the new cells can produce antibody, which is a soluble form of the glycoprotein receptor from the B cell’s surface. As this antibody is released, it binds to the invading antigen either rendering it inactive or causing its destruction through interaction with phagocytes. Some activated B cells become memory B cells which continue to produce a small amount of antibody after the infection is over. If the same pathogen enters the body again, the antibody immediately binds with the antigen and targets it for destruction.

Question 87

Describe the action of T cells

Answer 87

T cells also originate in bone marrow, but, as mentioned earlier, mature in the thymus gland. T cells contain specific antigen receptors. Killer T cells recognize and destroy invading cells containing foreign antigens. Killer T cells attack virus-infected cells, cancer cells and tissue grafts by releasing cytokines and enzymes which lyse the cell. Because tissue grafts or organ transplants often originate from another person’s body, the antigens on the surface of the graft are often recognized by the host body as a foreign pathogen. An identical twin can often make donations to his/her sibling without complications; however, those patients without an identical twin (most of us!) may need to be place on drugs that suppress the immune system. Eventually, the drug dosage can be lowered, but, until then, the patient is more susceptible to disease. Fortunately, some transplants, like corneal transplants, are highly successful because of the lack of blood and lymphatic vessels in that area. Helper T cells secrete substances that activate or enhance immune responses. B cells require an interaction with helper T cells before they can begin rapid division.

Question 88

What happens in allergic reactions ?

Answer 88

In allergic reactions antibodies are produced against mild antigens called allergens. These allergens are typically common environmental factors such as pollen or dust mites. Many people that display allergies have some type of genetic pre-disposition to this type of reaction

Question 89

What is meant by autoimmune disease?

Answer 89

This is a disease in which the immune system attacks a person’s own body.

It results when antibodies and T cells attack the body’s own tissues. In rheumatoid arthritis, T cells produce interleukins which cause inflammation. In multiple sclerosis antibodies prevent the formation of the myelin sheath around nerve cells, resulting in overall body weakness. We do not always know why autoimmune diseases occur, but a viral or bacterial infection often precedes the onset. Studies in molecular biology and genetics are making great strides in understanding the mechanisms of autoimmune disease.

Question 90

When it comes to blood being drained from the body back into the heart, where does blood from all different areas of the body drain into?

Answer 90

The superior and inferior vena cava

Anything above diaphragm is drained by superior vena cava. Anything below diaphragm is drained by the inferior vena cava.