Immune Disorders

The human body protects itself from diseases caused by microorganisms through an elaborate network of safeguards - the immune system.

The immune system: Structures and strategies

The immune system, also known as the host defense system, consists of physical and chemical barriers to infection as well as the inflammatory and immune responses.

Physical barriers - such as skin and mucous membranes-block invasion by most organisms. Harmful organisms that do penetrate these barriers simultaneously trigger a second line of defense: the inflammatory and immune responses. Both responses call on cells derived from a hematopoietic stem cell in bone marrow.

The inflammatory response mobilizes polymorphonuclear leukocytes, basophils, mast cells, and platelets. The immune response primarily involves forces of T lymphocytes (or T cells), B lymphocytes ( or B cells), macrophages, and macrophage-like cells and their products. Some of these cells circulate continuously, whereas others stand guard in the tissues and organs of the immune system, including the thymus, lymph nodes, Peyer's patches of the intestines, spleen, and tonsils.

The thymus contributes to the maturation of T cells ( the blood cells associated with cell-mediated immunity. Here, these cells are "educated" to differentiate self from nonself. In contrast, bone marrow serves as the site of B-cell maturation. B cells provide humoralimmunity. The key humoral effector mechanism is the complement cascade. The lymph nodes, spleen, and intestinal lymphoid tissue then help to destroy and remove antigens circulating in the blood and lymph.

Immune disorders

For various reasons, the complex processes involved in the host defense and immune response may malfunction. When the body's defenses are exaggerated, misdirected, absent, or depressed, the result may be a hypersensitivity, autoimmune, or immunodeficiency disorder, respectively.

Assessing the immune system

Performing an accurate assessment of the immune system can challenge your skills. Immune disorders may cause vague symptoms, which initially seem related to other body systems.

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