Question

It is a secondary lymphoid organ.

• A. Thymus gland
• B. Bone marrow
• C. Spleen
• D. Bursa of fabricius

Hint:

Distinguish between primary (thymus, bone marrow, Bursa of Fabricius in birds) and secondary (spleen, lymph nodes, tonsils, Peyer's patches, MALT) lymphoid organs based on their functions in lymphocyte maturation vs. immune response initiation.

Answer 1

The Correct Option is C

Step 1: Understand primary and secondary lymphoid organs

Primary (central) lymphoid organs: These are the sites where lymphocytes (B cells and T cells) are produced and mature into immunocompetent cells (cells capable of recognizing specific antigens). Examples include the bone marrow (where B cells mature and T cells originate) and the thymus (where T cells mature).
Secondary (peripheral) lymphoid organs: These are the sites where mature lymphocytes encounter antigens and are activated, proliferate, and differentiate into effector cells and memory cells. These are the sites where immune responses are initiated and carried out.

Step 2: Evaluate each option based on the definitions

• Thymus gland: The thymus gland is a primary lymphoid organ. It is the site where T lymphocytes (T cells) mature and undergo selection processes.
  This option is incorrect.
• Bone marrow: Bone marrow is a primary lymphoid organ. It is the site of hematopoiesis (formation of all blood cells, including lymphocytes) and the maturation of B lymphocytes (B cells). T lymphocytes also originate in the bone marrow before migrating to the thymus for maturation.
  This option is incorrect.
• Spleen: The spleen is a large, secondary lymphoid organ located in the upper left abdomen. It serves as a filter for blood, playing a crucial role in immune responses against blood-borne antigens. It contains B cells, T cells, and macrophages and is a major site for initiating adaptive immune responses.
  This option is correct.
• Bursa of Fabricius: The Bursa of Fabricius is a primary lymphoid organ found only in birds. It is the site of B cell maturation in birds, analogous to the bone marrow in mammals for B cell development.
  This option is incorrect as it’s not a secondary lymphoid organ and not found in mammals.

Step 3: Conclude the correct option

Among the given options, the spleen is a secondary lymphoid organ.

The final answer is: Spleen.