Exam 3 Review:  Chapter 21:  Lymphatic Organs

primary lymphatic organ - Those organs in which lymphocytes are produced or in which they mature; in the human, they are the red bone marrow (B lymphocytes) and the thymus gland (T lymphocytes).

red bone marrow - The type of marrow tissue found in spongy bone and marrow cavities where the various blood stem cells reside and where new red blood cells, white blood cells, and platelets are produced for release into the circulation.

thymus gland - A lobed endocrine organ located in the mediastinum, deep to the sternum, which is responsible for the maturation of T lymphocytes; it produces a number of local hormones including thymosin to contribute to T lymphocyte maturation; the thymus is at its largest at birth and shrinks over time, being replaced by fibrous connective tissue, and is usually absent by the end of the second decade of life.

secondary lymphatic organ  - Those organs in which mature lymphocytes are found and where they play active roles in immune defense reactions; in the human, they include the red bone marrow, the lymph nodes, the spleen, the tonsils and the various isolated microscopic lymphatic nodules, especially those found in lamina propria of mucous membranes of the GI tract, respiratory tract, urinary tract, and reproductive tract, i.e., “MALT” = mucosa-associated lymphatic tissue.

lymph node - Any of the small encapsulated bodies (secondary lymphatic organs) located along the lymphatic vessels, particularly at the neck, armpit, and groin, and in the thoracic and abdominal cavities, which receive lymph (interstitial fluid = intercellular fluid = tissue fluid) from the lymphatic circulation through afferent lymphatic vessels and filter microorganisms and foreign particles from the fluid; during infection, they may become swollen with activated lymphocytes.  aka -- lymph glands

tonsils - Small oral masses of lymphoid tissue covered by mucous membranes, especially either of two such masses embedded in the lateral walls of the opening between the mouth and the pharynx, which help, in a limited fashion, protect the throat from potential infections.

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