The Lymphatic System

Objectives

When you have completed this section, you should be able to

• list the functions of the lymphatic system;
• explain how lymph is formed and returned to the bloodstream; and
• describe the form and function of the lymph nodes, tonsils, thymus, and spleen.

Think About It

Contrast the structure of a lymphatic capillary with that of a continuous blood capillary. Explain why their structural difference is related to their functional difference.

Key Point Review

1. List the primary functions of the lymphatic system. What do you think would be the most noticeable effect of clamping the right lymphatic duct closed?

2. How does fluid get into the lymphatic system? What prevents it from draining back out?

3. Predict the relative seriousness of removing the following damaged or diseased organs from a 2-year-old child: (a) a lymph node, (b) the spleen, (c) the thymus, (d) the palatine tonsils.

Nonspecific Resistance

Objectives

When you have completed this section, you should be able to

• contrast nonspecific resistance with immunity;
• describe the process of inflammation and explain what accounts for its cardinal signs; and
• describe the body's other nonspecific defenses against pathogens.

Think About It

Review eicosanoid synthesis in chapter 17 and explain why aspirin eases the pain of inflammation.

Key Point Review

4. What are macrophages? Give four examples and state where they are found.

5. List the cardinal signs of inflammation and state the cause of each.

6. How do interferons and the complement system protect against disease?

7. Summarize the benefits of fever and the limits of this benefit.

General Aspects of Specific Immunity

Objectives

When you have completed this section, you should be able to

• define specific immunity;
• contrast humoral and cellular immunity;
• describe the chemical constitution of antigens and antibodies and sketch or describe the structure of an antibody molecule; and
• describe the general roles played by lymphocytes, macrophages, and interleukins in the immune response.

Think About It

Is clonal deletion a case of apoptosis or necrosis? (Review these concepts in chapters 4 and 6 if necessary.)

Key Point Review

8. How does specific immunity differ from nonspecific defense?

9. How does humoral immunity differ from cellular immunity?

10. What structural properties distinguish antigenic molecules from those that are not antigenic?

11. Explain the distinction between the variable region and the antigen-binding site of an immunoglobulin.

12. What is an immunocompetent lymphocyte? What does a lymphocyte have to produce in order to be immunocompetent?

13. Define T cell and B cell.

14. Define interleukin, lymphokine, and monokine.

Humoral Immunity

Objectives

When you have completed this section, you should be able to

• explain how B cells recognize and respond to an antigen;
• describe the actions of antibodies; and
• explain how immune memory prevents disease upon reexposure to an antigen.

Think About It

Explain why IgM has a stronger power of agglutination than antibodies of any other class.

Key Point Review

15. What are the three phases of an immune response?

16. What is an MHC protein? How does it relate to B cell and helper T cell function?

17. What is the difference between a B cell and a plasma cell?

18. Describe four ways in which an antibody reacts against an antigen.

19. Why does the secondary immune response prevent a pathogen from causing disease, while the primary immune response does not?

Cellular Immunity

Objectives

When you have completed this section, you should be able to

• list the types of lymphocytes involved in cellular immunity and describe the roles they play;
• describe the role of MHC proteins in the activation of helper and cytotoxic T cells;
• explain how interleukins coordinate the actions of immune system cells;
• contrast the roles played by helper, cytotoxic, and suppressor T cells; and
• compare and contrast the action of memory cells in cellular and humoral immunity.

Think About It

How is a killer T cell like a natural killer (NK) cell? How are they different?

Key Point Review

20. Name four types of lymphocytes that are involved in cellular immunity. Which of these is also essential to humoral immunity?

21. Explain why cytotoxic T cells are activated by a broader range of the body's cells than are helper T cells.

22. What positive feedback cycle can you identify in T cell clonal selection?

23. Why would a viral attack on helper T cells be especially devastating to a person's health?

24. Describe one way in which cytotoxic T cells destroy target cells.

Immune System Disorders

Objectives

When you have completed this section, you should be able to

• distinguish between the four types of hypersensitivity and give an example of each;
• explain the cause of anaphylaxis and distinguish local anaphylaxis from anaphylactic shock;
• explain the cause of asthma and describe how its symptoms are produced;
• state some reasons immune self-tolerance may fail, and give examples of the resulting diseases; and
• contrast severe combined immunodeficiency disease (SCID) with AIDS.

Key Point Review

25. Contrast local anaphylaxis and anaphylactic shock. Include an explanation of why the latter is more serious.

26. Explain why anaphylactic shock occurs immediately upon antigen exposure while the response to poison ivy takes much longer to develop.

27. Give three reasons why the immune system may become activated by the body's own antigens. Name or briefly describe a disease that exemplifies each mechanism.

28. How are SCID and AIDS similar? How are they different?

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