Lymphoid Organs

Human anatomy > Lymphatic System > Lymphoid Organs

Lymphoid organs form part of the body’s immune system. Lymphoid organs defend the body against invading pathogens that cause infections or spread of tumors. These organs exist as primary, secondary or tertiary, based on the stage of lymphocyte development and maturation the organ is involved in. These organs consist of connective tissues with different types of leukocytes or white blood cells. Lymphocytes usually present the highest percentage among these white blood cells regardless of the type of lymphoid organ (i.e. primary, secondary or tertiary). 

What are primary lymphoid organs?

The primary lymphoid organs serve to generate lymphocytes from immature progenitor cells. Progenitor cells possess the capacity to differentiate into a specific cell type. Progenitor cells divide for a limited number of times, depending on the need of the body.

Lymphoid organs

Immunologists occasionally refer to these organs as “central lymphoid organs.” Examples of primary lymphoid organs include the bone marrow and the thymus.  

What are secondary lymphoid organs?

Secondary lymphoid organs take charge of maintaining mature but naive lymphocytes. These organs initiate adaptive immune response. Immunologists refer to these organs as “peripheral lymphoid organs.”  Peripheral lymphoid organs serve as the site for lymphocyte activation. Antigen-presenting cells present antigens in these organs and this will lead to expansion and affinity maturation of the lymphocytes. Mature lymphocytes circulate in the blood and the peripheral lymphoid organs until they encounter the specific antigen. Examples of secondary or peripheral lymphoid organs include adenoids, the tonsils, lymph nodes, Peyer’s patches, the spleen, and even the skin, among others. All of these form the mucosa-associated lymphoid tissues.   

What are tertiary lymphoid organs?

The tertiary lymphoid tissue usually contains less number of lymphocytes. It plays an important role during inflammation. Inflammation forms part of the vascular response to unfavorable stimuli. Stimuli include pathogens, damaged cells or other irritants. Inflammation protects the body by removing harmful stimuli and initiating a healing process.

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