Which of the following is considered a primary lymphoid organ?
lymph node
tonsils
appendix
spleen
thymus
The Correct Answer is E
A. Lymph node: Lymph nodes are secondary lymphoid organs where lymphocytes encounter antigens and mount immune responses. They do not provide the environment for initial lymphocyte development or immunocompetence.
B. Tonsils: Tonsils are secondary lymphoid tissues that trap pathogens entering through the oral and nasal cavities. They function in immune surveillance but do not serve as sites for lymphocyte maturation.
C. Appendix: The appendix contains lymphoid tissue that contributes to immune defense, but it is a secondary lymphoid structure involved in antigen exposure, not lymphocyte development.
D. Spleen: The spleen filters blood and supports immune responses to blood-borne antigens. It is a secondary lymphoid organ and does not generate immunocompetent lymphocytes initially.
E. Thymus: The thymus is a primary lymphoid organ where T lymphocytes mature and acquire immunocompetence. It provides the essential environment for T cell differentiation before they enter circulation and secondary lymphoid tissues.
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Related Questions
Correct Answer is D
Explanation
A. Store iron from hemoglobin:The spleen breaks down old erythrocytes and stores the iron from hemoglobin for reuse in new red blood cell production. This storage function is an important aspect of its role in recycling nutrients.
B. House B and T lymphocytes:The spleen contains white pulp, which is rich in lymphocytes. It provides a site for immune surveillance and activation of B and T cells, supporting adaptive immune responses.
C. Remove and recycle old erythrocytes and platelets:The spleen filters blood, removing aged or damaged erythrocytes and platelets. Macrophages within the spleen phagocytose these cells and recycle their components, maintaining blood health.
D. Produce new erythrocytes in adults:In healthy adults, the spleen does not produce new erythrocytes. Erythropoiesis primarily occurs in the red bone marrow, making this option not a normal function of the spleen.
Correct Answer is D
Explanation
A. Antibody:Antibodies are produced by B cells after activation and clonal expansion. They do not determine which B cells will be selected; instead, they are the end product of the immune response.
B. Interferon:Interferons are signaling proteins that help modulate the immune response, particularly against viral infections. They do not directly influence the selection of B cells for clonal expansion.
C. Complement:The complement system enhances pathogen destruction and inflammation but does not select specific B cells for cloning. Its role is part of innate immunity, not clonal selection.
D. Antigen:Antigens bind to specific B cell receptors, selecting which B cells will proliferate. Only B cells whose receptors recognize the antigen undergo clonal expansion, differentiating into plasma cells and memory B cells, which ensures a targeted adaptive immune response.
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