Concepts of Human Anatomy & Physiology   5/e   Van De Graaff/Fox
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I. Lymphatic System

Concept: The lymphatic system, consisting of lymphatic vessels and various lymphoid tissues and organs, helps to maintain fluid balance in the tissues and to absorb fats from the gastrointestinal tract. It is also part of the body's defense system against disease.

II. Defense Mechanisms

Concept: Nonspecific immune protection is provided by such mechanisms as phagocytosis, fever, and the release of interferons. Specific immunity, which involves the functions of lymphocytes, is directed at specific molecules, or parts of molecules, known as antigens.

III. Functions of B Lymphocytes

Concept: B lymphocytes secrete antibodies that can bind to antigens in a specific fashion. This binding stimulates a cascade of reactions whereby a system of plasma proteins called complement is activated. Some of these activated complement proteins kill the cells containing the antigen; others promote phagocytosis and other activity that result in a more effective defense against pathogens.

IV. Active and Passive Immunity

Concept: When a person is first exposed to a pathogen, the immune response may be insufficient to combat the disease. In the process, however, the lymphocytes that have specificity for that antigen are stimulated to divide many times and produce a clone. This is active immunity, and it can protect the person from getting a disease upon subsequent exposures.

V. Functions of T Lymphocytes

Concept: Each subpopulation of T lymphocytes has specific immune functions. Killer T cells effect cell-mediated destruction of specific victim cells, and helper and supressor T cells play supporting roles. T cells are activated only by antigens presented to them on the surface of particular antigen-presenting cells. Activated helper T cells produce lymphokines that stimulate other cells of the immune system.

VI. Tumor Immunology

Concept: Tumor cells can reveal antigens that stimulate the destruction of the tumor. When cancers develop, this immunological surveillance system-primarily the function of T cells and natural killer cells-has failed to prevent the growth and metastasis of the tumor.

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