Shier, Butler, and Lewis: Hole’s Human Anatomy and Physiology, 10th ed.
Chapter 16: Lymphatic System and Immunity
A. The lymphatic system is closely associated with the cardiovascular system because it includes a network of vessels that assist in circulating body fluids.
B. Lymphatic vessels transport excess fluid away from interstitial spaces and return it to the bloodstream.
C. Lacteals are lymphatic capillaries in the lining of the small intestine and function to transport fats to the venous system.
D. The organs of the lymphatic system also defend the body against infection by disease-causing agents.
A. Lymphatic Capillaries
1. Lymphatic capillaries are microscopic, closed-ended tubes that extend into interstitial spaces.
2. The walls of lymphatic capillaries are similar to blood capillaries.
3. The thin walls of capillaries make it possible for tissue fluid from interstitial space to enter the lymphatic capillaries.
4. Lymph is fluid inside a lymphatic capillary.
B. Lymphatic Vessels
1. The walls of lymphatic vessels are similar to those of veins.
2. Lymphatic vessels have valves that prevent backflow of lymph.
3. Larger lymphatic vessels lead to lymph nodes.
4. After leaving nodes, lymphatic vessels merge together to form lymphatic trunks.
C. Lymphatic Trunks and Collecting Ducts
1. Lymphatic trunks drain lymph from lymphatic vessels and are named for the regions they serve.
2. Examples of lymphatic trunks are lumbar, intestinal, intercostal, bronchomediastinal, subclavian, and jugular trunks.
3. Lymphatic trunks join one of two collecting ducts.
4. The two collecting ducts are the thoracic duct and right lymphatic duct.
5. The thoracic duct is located along side the aorta in the abdominal and thoracic cavity and empties into the left subclavian vein.
6. The thoracic duct drains lymph from the intestinal, lumbar, and intercostal trunks, as well as from the left subclavian, left jugular, and left bronchomediastinal trunks.
7. The right lymphatic duct is located on the right side of the thorax and empties into the right subclavian vein.
8. The right lymphatic duct drains right jugular, right subclavian, and right bronchomediastinal trunks.
9. After leaving the two collecting ducts, lymph enters the venous system and becomes part of the plasma.
A. Introduction
1. Lymph is tissue fluid that has entered a lymphatic capillary.
2. Lymph formation depends on tissue fluid formation.
B. Tissue Fluid Formation
1. Capillary blood pressure filters water and small molecules from plasma and the resulting fluid consists of water, nutrients, gases, and hormones (a similar composition to plasma).
2. Water is drawn back into capillaries because of plasma colloid osmotic pressure.
C. Lymph Formation
1. Filtration from the plasma normally exceeds reabsorption, leading to the formation of tissue fluid.
2. Tissue fluid moves into lymphatic capillaries because of interstitial fluid hydrostatic pressure.
3. Lymph formation prevents edema.
D. Lymph Function
1. Lymphatic vessels in the small intestine play a major role in the absorption of dietary fats.
2. Lymph returns very small proteins that the blood capillaries filtered to the bloodstream.
3. Lymph transports foreign particles to lymph nodes.
4. Lymphatic capillaries can receive proteins and foreign particles that blood capillaries cannot because the epithelial cells that form the walls of lymphatic vessels overlap each other but are not attached.
5. The lumen of a lymphatic capillary remains open because their epithelial cells are attached to surrounding connective tissue cells by protein filaments.
A. Introduction
1. The hydrostatic pressure of tissue fluid drives lymph into lymphatic capillaries.
2. Muscular activity largely influences movement of lymph through lymphatic vessels.
B. Lymph Flow
1. Lymph is under relatively low hydrostatic pressure.
2. Contracting skeletal muscles compress lymphatic vessels.
3. Lymph does not flow back because of valves.
4. Breathing aids lymph circulation by creating a relatively low pressure in the thorax and a relatively high pressure in the abdomen during inhalation.
C. Obstruction of Lymph Movement
1. Conditions that interfere with lymph movement causes fluid to accumulate within interstitial spaces.
2. The continuous movement of lymph from interstitial spaces into blood capillaries and lymphatic capillaries stabilizes the volume of fluid in interstitial spaces.
A. Introduction
1. Lymph nodes are located along lymphatic pathways.
2. Lymph nodes contain lymphocytes and macrophages which fight invading microorganisms.
B. Structure of a Lymph Node
1. The hilum of a lymph node is the indented region.
2. Afferent lymphatic vessels are those that carry lymph to a node.
3. Efferent lymphatic vessels are those that carry lymph away from a node.
4. Lymph nodules are divisions of a lymph node.
5. Germinal centers contain dense masses of actively dividing lymphocytes and macrophages.
6. Tonsils are composed of partially encapsulated lymph nodules.
7. Peyer’s patches are located in the mucosal lining of the distal portion of the small intestine and are composed of M cells, macrophages, and lymphocytes.
8. Lymph sinuses are a network of chambers and channels through which lymph circulates.
C. Locations of Lymph Nodes
1. Lymph nodes generally occur in groups or chains along the paths of larger lymphatic vessels but are absent in the central nervous systems.
2. Major locations of lymph nodes are cervical region, axillary region, inguinal region, pelvic cavity, abdominal cavity, thoracic cavity, and supratrochlear region.
3. Lymph nodes of the cervical region are associated with lymphatic vessels that drain the skin of the scalp and fact, as well as tissues of the nasal cavity and pharynx.
4. Lymph nodes of the axillary region are associated with lymphatic vessels that drain the upper limbs, wall of the thorax, mammary glands, and upper abdominal wall.
5. Lymph nodes of the inguinal region are associated with lymphatic vessels that receive lymph from the lower limbs, external genitalia, and lower abdominal wall.
6. Lymph nodes of the pelvic cavity are associated with lymphatic vessels that drain the pelvic viscera.
7. Lymph nodes of the abdominal cavity are associated with lymphatic vessels that drain the abdominal viscera.
8. Lymph nodes of the thoracic cavity are associated with lymphatic vessels that drain thoracic viscera and the internal wall of the thorax.
9. Lymph nodes of the supratrochlear region are associated with lymphatic vessels that drain the elbow region.
D. Functions of Lymph Nodes
1. The two primary functions of lymph nodes are to filter potentially harmful particles from lymph and to monitor body fluids.
2. Along with the red bone marrow, lymph nodes are centers for lymphocyte production.
3. Lymphocytes attack viruses, bacteria, and other parasitic cells.
4. The functions of macrophages are to engulf and destroy foreign substances, damaged cells, and cellular debris.
A. Thymus
1. The thymus is composed of lymphocytes and connective tissues
and is located in the mediastinum .
2. After puberty, the thymus begins to shrink.
3. Most cells of the thymus gland are thymocytes.
4. The hormones secreted by the thymus gland are called thymosins.
5. Thymosins function to stimulate maturation of T lymphocytes.
B. Spleen
1. The largest lymphatic organ is the spleen.
2. The spleen is located in the upper left portion of the abdominal cavity.
3. The spleen resembles a large lymph node.
4. White pulp contains many lymphocytes.
5. Red pulp contains red blood cells, lymphocytes, and macrophages.
6. The functions of the spleen are to remove foreign particles, damaged red blood cells, and cellular debris from the blood.
VIII. Body Defenses Against Infection
A. A pathogen is disease-causing agents.
B. An infection is the presence of pathogens.
C. Examples of pathogens are bacteria, viruses, and fungi.
D. Innate defenses are general defenses and protect against many types of pathogens and include species resistance, mechanical barriers, enzyme actions, interferon, fever, natural killer cells, inflammation, and phagocytosis.
E. Adaptive defenses are very precise defense mechanisms and are carried out by lymphocytes.
IX. Innate Defenses
A. Species Resistance
1. Species resistance refers to the fact that a given kind of organism or species develops diseases that are unique to it.
2. A species may be resistant to diseases that affect other species because its tissues somehow fail to provide the temperature of chemical environment that a particular pathogen requires.
B. Mechanical Barriers
1. Mechanical barriers prevent the entrance of some infectious agents.
2. Examples of mechanical barriers are skin, mucous membranes, and hair.
3. The first line of defense is a mechanical barrier.
4. The second line of defense is a collection of the other nonspecific defenses.
C. Chemical Barriers
1. Chemical barriers are body fluids containing enzymes or antimicrobial substances.
2. Examples of chemical barriers are gastric juice, interferons, defensins, and collectins.
3. Interferon is produced by lymphocytes and fibroblasts and its functions include stimulation of phagocytosis, and to prevent viral infections.
4. Defensins are produced by white blood cells, and certain epithelial cells.
5. The functions of defensins are to make holes in bacterial cells walls and to destroy certain pathogens.
6. Collectins are proteins and their functions include protecting the body against viruses, bacteria, and yeasts.
D. Fever
1. A fever begins when a viral or bacterial infection stimulates lymphocytes to produce interleukin-1.
2. The functions of fever are to increase phagocytosis and to prevent bacteria and other pathogens from obtaining iron.
E. Natural Killer Cells
1. Natural killer cells are a small population of lymphocytes.
2. Functions of natural killer cells are to protect the body against cancer and viruses.
3. Perforins are cytolytic substances secreted by natural killer cells.
F. Inflammation
1. Inflammation produces redness, swelling, heat and pain.
2. Redness of inflammation is the result of dilated blood vessels.
3. Swelling of inflammation is the result of increases capillary permeability.
4. Heat of inflammation is the result of the entry of blood from deeper body parts.
5. Pain of inflammation is the result of stimulation of pain receptors.
6. Cells that commonly migrate to areas of inflammation are neutrophils and monocytes.
7. Pus is the result of an accumulation of white blood cells, bacterial cells, and cellular debris.
8. The functions of inflammation are to prevent the spread of infection, to clear infection, and to promote healing of damaged tissues.
G. Phagocytosis
1. Phagocytosis removes foreign particles.
2. Examples of phagocytic cells are neutrophils, monocytes, and macrophages.
3. The mononuclear phagocytic system is monocytes, macrophages, and neutrophils that are spread throughout the body.
X. Adaptive Defenses or Immunity
A. Introduction
1. Immunity is resistance to particular pathogens or to their toxins or metabolic by-products.
2. An immune response is based on the ability to distinguish molecules that are part of the body from those that are foreign.
3. Antigens are molecules that can elicit an immune response.
4. Lymphocytes and macrophages carry out immune responses.
B. Antigens
1. Receptors on lymphocyte surfaces enable cells to recognize foreign antigens.
2. Antigens may be proteins, polysaccharides, glycoproteins, or glycolipids.
3. The antigens most effective in eliciting an immune response is large and complex, with few repeating parts.
4. A hapten is a small molecule that must bind to a larger molecule to elicit an immune response.
5. Examples of haptens are chemicals found in drugs, household cleaners, dust, and skins of certain animals.
C. Lymphocyte Origins
1. T cells are derived from red bone marrow and the thymus gland.
2. B cells are derived from red bone marrow.
3. The blood distributes B cells.
4. B cells and T cells are abundant in lymph nodes, the spleen, bone marrow, and the intestinal lining.
D. Lymphocyte Functions
1. The cellular immune response is cell-to-cell contact between a T cell and antigen cell.
2. Cytokines are produces by T cells.
3. Examples of cytokines are interleukins, colony-stimulating factors, interferons, and tumor necrosis factors.
4. Functions of cytokines are to stimulate the production of lymphocytes, block viral replication, stimulate phagocytosis, stimulate production of antibodies, and to stop growth of tumor cells.
5. T cells may also secrete toxins that kill antigen-bearing cells, growth-inhibiting factors that prevent target cell growth, or interferon that prevent viral and tumor cell proliferation.
6. B cells differentiate into plasma cells.
7. Plasma cells produce antibodies.
8. The humoral immune response is the immune response that is mediated by antibodies.
9. A clone is a cell that is identical to the cell from which it was derived.
10. Different varieties of T cells and B cells have a particular type of antigen receptor on their cell membranes that can respond only to a specific antigen.
E. T Cells and the Cellular Immune Response
1. A lymphocyte must be activated before it can respond to an antigen.
2. T cell activation requires the presence of processed fragments of antigen attached to the surface of another kind of cell.
3. Antigen-presenting cells are macrophages, B cells, and other cell types.
4. T cell activation begins when a macrophage phagocytizes a bacterium and moves the antigens of the bacterium to its membrane.
5. The major histocompatibility complex is a complex of proteins found on the surface of antigen-presenting cells.
6. MHC antigens help T cells recognize an antigen as foreign.
7. Class I MHC antigens are located on cell membranes of all cells except red blood cells.
8. Class II MHC antigens are located on cell membranes of antigen-presenting cells, thymus cells, and activated T cells.
9. The functions of helper T cells are to stimulate B cells to produce antigens and to secrete cytokines.
10. The functions of cytotoxic T cells are to eliminate viral infected cells and tumor cells.
11. The functions of memory T cells are to respond to an antigen during a future exposure and to differentiate immediately into cytotoxic T cells.
F. B Cells and the Humoral Immune Response
1. Introduction
a. B cells may become activated when an antigen binds to its membrane-bound receptor.
b. Upon activation, B cells divide repeatedly.
c. T cells help B cells by releasing cytokines that stimulate B cell proliferation and antibody production.
d. The functions of memory B cells are to respond rapidly to subsequent exposures to a specific antigen.
e. The functions of plasma cells are to secrete antibodies.
f. An immune response may include several types of antibodies manufactured against a single microbe because pathogens often have different antigens on their surfaces.
g. A polyclonal response is the production of several different antibodies against one pathogen.
2. Antibody Molecules
a. Antibodies are soluble, globular proteins
b. Each antibody is composed of four chains of amino acids that are linked together.
c. The light chains are identical and contain about half the number of amino acids as the heavy chains.
d. The heavy chains are identical and contain twice as many amino acids as the light chains.
e. The five major types of antibodies are distinguished by a particular kind of heavy chain.
f. The variable region is the part of the antibody that contains variable regions of amino acids.
g. Variable regions are specialized to react to the shape of a specific antigen molecule.
h. Antigen-binding sites are specialized ends of antibodies that bind to antigens.
i. Idiotypes are the particular parts of antigen-binding sites that actually bind to antigens.
j. Constant regions are the parts of an antibody other than their variable regions.
3. Types of Immunoglobulins
a. The five major types of immunoglobulins are IgG, IgA, IgM, IgD, and IgE.
b. The three types of immunoglobulins that make up the bulk of circulating antibodies are IgG, IgA, and IgM.
c. IgG is found in tissue fluid and plasma.
d. The functions of IgG are to defend against bacterial, viruses, and toxins; it also activates complement.
e. IgA is found in exocrine gland secretions.
f. The functions of IgA are to defend against bacteria and viruses.
g. IgM is found in plasma.
h. The functions of IgM are to react with antigens occurring on red blood cells and to activate complement.
i. IgD is found in the cell membranes of B cells.
j. The functions of IgD are to act as receptors for B cells.
k. IgE is located in exocrine gland secretions.
l. The functions of IgE are to promote inflammation and allergic reactions.
4. Antibody Actions
a. The three ways antibodies react to antigens are to directly attack antigens, activate a set of enzymes that attack antigens, or stimulate localized changes that help prevent the spread of the antigens.
b. In a direct attack, antibodies combine with antigens and cause them to clump.
c. Phagocytic cells can engulf antigens more readily when they have clumped together.
d. Antibodies can also cover the toxic portions of antigens and neutralize their effects.
e. Complement is a group of proteins in plasma and other body fluids.
f. Complement is activated by the binding of certain antibodies to antigens.
g. Functions of complement are opsonization, chemotaxis, cell lysis, and inflammation.
h. IgE antibodies are usually attached to membranes of mast cells.
i. Mast cells release their biochemicals when antigens combine to antibodies on their surfaces.
G. Immune Responses
1. The primary immune response occurs when a person is first exposed to an antigen.
2. Following a primary immune response, some B cells produce memory cells.
3. The secondary immune response occurs when a person is later exposed to an antigen and memory cells are activated.
H. Practical Classification of Immunity
1. Naturally acquired active immunity develops when a person is naturally exposed to an antigen.
2. Artificially acquired active immunity develops when a person is given a vaccine.
3. A vaccine is an injection of a dead or weakened antigen that promotes an immune response.
4. Artificially acquired passive immunity occurs when a person is injected with antibodies or anti-toxins.
5. Naturally acquired passive immunity occurs when antibodies are passed across the placenta or through mother’s milk.
I. Allergic Reactions
1. An allergic reaction is an immune response against a nonharmful substance.
2. Allergens are substances that trigger allergic reactions.
3. An immediate-reaction allergy occurs when an allergens bind to IgE antibodies and allergy mediators are released from mast cells and basophils.
4. Anaphylactic shock is a severe form of immediate-reaction allergy that may lead to death.
5. Antibody-dependent cytotoxic reactions occur when an antigen binds a specific cell, simulating phagocytosis and complement-mediated lysis of the antigen.
6. Immune complex reactions occur when antigen-antibody complexes cannot be cleared from the body.
7. Autoimmunity refers to the loss of the ability to tolerate self-antigens.
8. A delayed-reaction allergy occurs when a person is repeatedly exposed to an allergen and the allergic reaction occurs about 48 hours after exposure to the antigen.
J. Transplantation and Tissue Rejection
1. Transplanted tissues and organs include corneas, kidneys, lungs, pancreases, bone marrow, skin, livers, and hearts.
2. A tissue rejection reaction is the destruction of transplanted tissue by the recipient’s immune system.
3. Tissues are rejected because the cell surface molecules (MHC antigens) of the donor tissue are recognized as foreign by the recipient.
4. Isografts are grafts from an identical twin.
5. Autografts are grafts from one’s self.
6. Allografts are grafts from another person.
7. Xenografts are grafts from a different species.
8. Immunosuppressive drugs are used to reduce rejection of transplanted tissues.
K. Autoimmunity
1. Autoantibodies are antibodies that cannot distinguish self from nonself.
2. Reasons people develop autoimmunities are viruses may incorporate some self proteins into its coating and the body then recognizes the self proteins as foreign in all cells, T cells may never learn to differentiate between self and nonself cells, or some antigens may resemble self antigens.
3. Scleroderma is a condition caused by autoimmunity that produces fatigue, swollen joints, stiff fingers, hardened blood vessels, and a mask like face.
A. The immune system begins to decline early in life.
B. By age 70, the thymus is one-tenth of its original size.
C. Elderly people have a higher risk of developing cancer and infections because the strength of their immune systems has declined.
D. AIDS is more difficult to diagnose in older people because physicians do not initially suspect the condition.
E. Elderly people may not be candidates for certain medical treatments because of their declining immune systems.
Chapter 16
Lymphatic System and Immunity
16.1 Introduction
1. Explain the functions of the lymphatic system. (p. 617)
Lymphatic vessels transport excess fluid away from the interstitial spaces in most tisues and return it to the bloodstream.
16.2 Lymphatic Pathways
2. Trace the general pathway of lymph from the interstitial spaces to the bloodstream. (p. 617)
The lymphatic capillary system is found next to the systemic and pulmonary capillary networks. It then travels through lymph vessels into lymph nodes. It returns to lymph vessels and then is returned into the bloodstream at various points.
16.3 Tissue Fluid and Lymph
3. Distinguish between tissue fluid and lymph. (p. 619)
Lymph is tissue fluid that has entered into a lymphatic capillary.
4. Describe the primary functions of lymph. (p. 620)
The primary functions of lymph are to return the proteins to the bloodstream that has leaked out of the blood capillaries and to transport bacteria and other foreign particles to the lymph nodes.
16.4 Lymph Movement
5. Explain why physical exercise promotes lymphatic circulation. (p. 621)
The contractions of the skeletal muscles, pressure changes due to the actions of breathing muscles, and smooth muscle contractions of the larger lymphatic trunks all aid in the movement of lymph through the body.
6. Explain how a lymphatic obstruction leads to edema. (p. 621)
Continuous movement of fluid from the interstitial spaces into the lymphatic system stabilizes the volume of fluids in these spaces. When an obstruction occurs, the tissue fluid builds up and causes edema.
16.5 Lymph Nodes
7. Draw a lymph node, and label its parts. (p. 621)
See textbook for illustration.
8. On a drawing of the body locate the major body regions containing lymph nodes. (p. 622)
The major body regions include: cervical region, axillary region, inguinal region, pelvic cavity, abdominal cavity, thoracic cavity, and supratrochlear region.
See textbook for illustration.
9. Explain the functions of a lymph node. (p. 623)
Each lymph node is enclosed in a capsule of fibrous connective tissue and subdivides into compartments. The compartments contain dense masses of lymphocytes and macrophages. These masses, called nodules, are the structural units of a lymph node. Lymph nodes function in lymphocyte production and phagocytosis of foreign substances, damaged cells, and cellular debris.
16.6 Thymus and Spleen
10. Indicate the locations of the thymus and spleen. (p. 623)
The thymus is in the mediastinum, anterior to the aortic arch and posterior to the upper part of the body of the sternum, and extends from the root of the neck to the pericardium. The spleen is in the upper left portion of the abdominal cavity, just inferior to the diaphragm, posterior and lateral to the stomach.
11. Compare and contrast the functions of the thymus and spleen. (p. 623)
The thymus is a soft, bilobed structure whose lobes are surrounded by a capsule of connective tissue. It is composed of lymphatic tissue, which is subdivided into lobules by connective tissues. The lobules contain many lymphocytes. It functions to produce T-lymphocytes that help in the immune response. It also secretes thymosin, which is thought to stimulate the maturation of T-lymphocytes after they leave the thymus.
The spleen is the largest lymphatic organ. It resembles a large lymph node and is subdivided into chambers or lobules. The spaces within the chambers are filled with blood instead of lymph. There are two types of tissues within the lobules of the spleen. They include:
White pulp—distributed throughout the spleen in tiny islands, composed of splenic nodules, and containing large numbers of lymphocytes.
Red pulp—surrounds the venous sinuses and contains many red blood cells along with numerous lymphocytes and macrophages.
The spleen functions to filter the blood.
16.7 Body Defenses Against Infection
12. Defense mechanisms that prevent the entry of many types of pathogens and destroy them if they enter provide __________ (nonspecific) defense. Mechanisms that are very precise, targeting specific pathogens provide ___________ (specific) defense. (p. 626)
innate, adaptive
16.8 Innate (Nonspecific) Defenses
13. Define species resistance. (p. 626)
Species resistance is referring to the fact that a given kind of organism or species develops diseases that are unique to it. A species may be resistant to diseases that affect other species, because its tissues somehow fail to provide the temperature or chemical environment needed by a particular pathogen.
14. Identify the barriers that provide the body’s first line of defense against infectious agents. (p. 626)
The skin, hair, and the mucous membranes are three mechanical barriers to infection.
15. Describe how enzymatic actions function as defense mechanisms against pathogens. (p. 626)
Enzymes provide a chemical barrier to pathogens. By splitting components of the pathogen or decreasing the pH, the enzyme can have lethal effects on pathogens.
16. Distinguish among the chemical barriers (interferons, defensins, collectins, and complement proteins), and give examples of their different actions. (p. 626)
Interferons stimulate uninfected cells to synthesize antiviral proteins that block proliferation of viruses; stimulate phagocytosis; and enhance activity of cells that help resist infections and stifle tumor growth.
Defensins make holes in bacterial cell walls and membranes.
Collectins provide broad protection against a wide variety of microbes by grabbing onto them.
Activation of complement proteins in plasma stimulates inflammation, attracts phagocytes, and enhances phagocytosis.
17. Describe natural killer cells and their actions. (p. 627)
NK cells are a small population of lymphocytes. NK cells defend the body against various viruses and cancer by secreting cytolytic substances called perforins.
18. List the major effects of inflammation. (627)
Localized redness—result of blood vessel dilation and the increase in blood volume of affected tissues.
Swelling—result of increased blood volume and increased permeability of nearby capillaries.
Heat—due to the presence of blood from deeper body parts, which is generally warmer than that near the surface.
Pain—results from the stimulation of nearby pain receptors.
19. Identify the major phagocytic cells in the blood and other tissues. (p. 627)
The most active phagocytic cells of the blood are neutrophils and monocytes. Macrophages are fixed phagocytic cells found in lymph nodes, spleen, liver, and lungs. This constitutes reticuloendothelial tissue.
20. List possible causes of fever, and explain the benefits of fever. (p. 628)
Viral or bacterial infection stimulates certain lymphocytes to secrete IL-1, which temporarily raises body temperature.
Physical factors, such as heat or ultraviolet light, or chemical factors, such as acids or bases, can cause fever.
Elevated body temperature and the resulting decrease in blood iron level and increased phagocytic activity hamper infection.
16.9 Adaptive (Specific) Defenses, or Immunity
21. Distinguish between an antigen and a hapten. (p. 628)
An antigen is a foreign substance, such as a protein, polysaccharide or a glycolipid, to which lymphocytes respond. A hapten is a molecule that by itself cannot stimulate the immune response. It must combine with a larger molecule.
22. Review the origin of T cells and B cells. (p. 628)
T cells originate in the thymus. B cells are those processed in another part of the body, probably the fetal liver.
23. Define clone of lymphocytes. (p. 629)
The members of each variety of B and T cells originate from a single early cell. Therefore, they are all alike, forming a clone, genetically identical cells originating from division of a single cell.
24. Explain the cellular immune response, including the activation of T cells. (p. 630)
The lysosomal digestive process of phagocytosis of an invading bacterium releases antigens. They are moved to the macrophage’s surface membrane. They are then displayed on the membrane with major histocompatibility complex. If the antigen then fits the helper T cell, it becomes activated. At this point, the helper T cell seeks out the appropriate T cell and by attaching to it, activates the T cell into a response. Cell-mediated immunity (CMI) is when a T cell, for example, attaches itself to antigen-bearing cells and interacts with the foreign cells directly.
25. Define cytokine. (p. 630)
Cytokines (lymphokines) are a variety of polypeptides that are synthesized and secreted by T cells and macrophages. These enhance various cellular responses to antigens. They stimulate the synthesis of lymphokines from other T cells, help activate resting T cells, cause T cells to proliferate, stimulate the production of leukocytes in the red bone marrow, cause growth and maturation of B cells, and activate macrophages.
26. List three types of T cells and describe the function of each in the immune response. (p. 630)
a. Helper T cells—mobilize the immune system to stop a bacterial infection through a series of complex steps.
b. Memory T cells—provide for no delay in the response to future exposures to an antigen.
c. Cytoxic T cells—recognize non-self antigens that cancerous or virally infected cells display on their surfaces.
27. Explain the humoral (immune) response, including the activation of B cells. (p. 632)
A B cell is activated when it binds to an activated T cell.
An activated B cell proliferates, enlarging its clone.
Some activated B cells specialize into antibody-producing plasma cells.
Antibodies react against the antigen-bearing agent that stimulated their production.
An individual’s diverse B cells defend against a very large number of pathogens.
B cells become activated when they encounter an antigen whose molecular shape fits the shape of the B cell’s antigen receptors. As a result of this combination, the B-cells proliferate by mitosis and its clone is enlarged.
This mechanism for activation is similar to the lock and key model used by enzymes and substrates.
28. Explain the function of plasma cells. (p. 632)
Plasma cells are some of the newly formed members of the activated B cell’s clone. They make use of their DNA information and protein-synthesizing mechanism to produce antibody molecules.
29. Describe an antibody molecule. (p. 634)
An antibody molecule consists of two identical light chains of amino acids and two identical heavy chains of amino acids.
30. Distinguish between the variable region and the constant region of an antibody molecule. (p. 634)
Variable regions are the portion of one end of each of the heavy and light chains consisting of variable sequences of amino acids making them specific for specific antigen molecules. Constant regions are the remaining portions of the chains whose amino acid sequences are very similar from molecule to molecule.
31. Match the types of antibodies with their function and/or where each is found. (p. 635)
1. Associated with allergic reactions—IgE
2. Important in B cell activation, on surfaces of most B cells—IgD
3. Activates complement, anti-A and anti-B in blood—IgM
4. Effective against bacteria, viruses, toxins in plasma and tissue fluids—IgG
5. In exocrine secretions, including breast milk—IgA
32. Describe three ways in which an antibody’s direct attack on an antigen helps remove that antigen. (p. 635)
Agglutination—antibodies combine with antigens and clumping results.
Precipitation—antibodies combine with antigens and insoluble substance forms.
Neutralization—antibodies cover the toxic portions of antigen molecules and neutralize their effects.
Lysis—antibodies cause the cell membranes to rupture.
33. Explain the functions of complement. (p. 635)
It is a group of inactive enzymes that become activated when certain IgG or IgM antibodies combine with antigens and the reactive sites become exposed. The activated enzymes produce chemotaxis, agglutination, opsonization, and lysis. It can also promote the inflammation reaction.
34. Contrast a primary and a secondary immune response. (p. 635)
A primary immune response occurs when B cells or T cells become activated after first encountering the antigens to which they are specifically reactant. A secondary immune response happens when memory cells are activated and increased in size, so they can respond rapidly to the antigen to which they were previously sensitized.
35. Contrast active and passive immunity. (p. 638)
Active immunity can be either naturally acquired or artificially acquired. Naturally acquired active immunity is stimulated as a result of exposure to live pathogens. Artificially acquired active immunity is stimulated by exposure to a vaccine containing weakened or dead pathogens. Passive immunity can also be either naturally acquired or artificially acquired. Naturally the antibodies passed to a fetus from a mother with active immunity stimulate acquired passive immunity. Artificially acquired passive immunity is stimulated by an injection of gamma globulin that contains antibodies.
36. Define vaccine. (p. 638)
A vaccine is a substance that contains an antigen that can stimulate a primary immune response against a particular disease-causing agent, but does not cause severe disease symptoms.
37. Explain how a vaccine produces its effect. (p. 638)
A vaccine contains bacteria or viruses that have been killed or weakened so they cannot cause a serious infection; or it may contain a toxin of an infectious organism that has been chemically altered to destroy its toxic effects. The antigens present still retain the characteristics needed to simulate a primary immune response.
38. Describe how a fetus may obtain antibodies from maternal blood. (p. 638)
Receptor-mediated endocytosis utilizing receptor sites on cells of the fetal yolk sac transfers IgG molecules to the fetus.
39. Explain the relationship between an allergic reaction and an immune response. (p. 639)
Allergic reactions are closely related to immune responses in that both may involve the sensitizing of lymphocytes or the combining of antigens with antibodies. Allergic reactions are likely to be excessive and to cause tissue damage.
40. Distinguish between an antigen and an allergen. (p. 639)
An antigen is a substance that stimulates cells to produce antibodies. An allergen is a foreign substance capable of stimulating an allergic reaction.
41. Describe how an immediate-reaction allergic response may occur. (p. 639)
In an immediate-reaction allergy, the individuals have an inherited ability to synthesize abnormally large quantities of antibodies in response to certain antigens. In this instance, the allergic reaction involves the activation of B-cells.
42. List the major events leading to a delayed-reaction allergic response. (p. 641)
It results from repeated exposure of the skin to certain chemical substances. As a consequence of these repeated contacts, the foreign substance and a large number of T cells collect in the skin and eventually activate the T cells. Their actions and the actions of macrophages they attract cause the release of various chemical factors. This causes eruptions and inflammation of the skin. It is called delayed since it takes about forty-eight hours to occur.
43. Explain the relationship between tissue rejection and an immune response. (p. 641)
Tissue rejection is when the immune system sees transplanted tissue as foreign and starts the immune response to try to rid the body of it.
44. Describe two methods used to reduce the severity of a tissue rejection reaction. (p. 641)
Matching the donor and recipient tissues may reduce it. It can also involve giving drugs that suppress the immune system.
45. Explain the goal of using immunosuppressive drugs before a transplant. (p. 641)
An immunosuppressive drug interferes with the recipient’s immune response by suppressing formation of antibodies or production of T cells. This will ultimately leave the recipient relatively unprotected against infection.
46. Explain the relationship between autoimmunity and an immune response. (p. 641)
Autoimmunity occurs when the immune system does not distinguish between self and nonself and manufactures autoantibodies that attack the body’s own cells. For whatever reason, the autoantibodies treat a certain cell type in the body as a foreign object and signal the immune system to defend against the perceived invader.
16.10 Life-Span Changes
47. Explain the causes for a decline in the strength of the immune response in the elderly. (p. 644)
The immune system begins to decline early in life, in part due to the decreasing size of the thymus.
Numbers of T cells and B cells do not change significantly, but activity levels do.
Proportions of the different antibody classes shift.
Source: http://highered.mheducation.com/sites/dl/free/0077262557/631246/Chapter_16.doc
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