Which of the following are primary lymphoid organs?
spleen and thymus
lymph nodes and tonsils
bone marrow and thymus
appendix and spleen
The correct answer and explanation is :
Correct Answer:
Bone marrow and thymus
Explanation:
Lymphoid organs are classified into primary (central) lymphoid organs and secondary (peripheral) lymphoid organs based on their function in the immune system.
Primary Lymphoid Organs
Primary lymphoid organs are responsible for the production and maturation of lymphocytes (a type of white blood cell). These organs include:
- Bone Marrow – The site of hematopoiesis (blood cell production), including the generation of B cells, T cell precursors, and other immune cells. B cells mature in the bone marrow before migrating to secondary lymphoid organs.
- Thymus – The site of T cell maturation. Immature T cells (thymocytes) from the bone marrow travel to the thymus, where they undergo selection processes to ensure they can properly recognize antigens without attacking the body’s own tissues.
Secondary Lymphoid Organs
Secondary lymphoid organs are where mature lymphocytes interact with antigens and initiate an immune response. These include:
- Spleen – Filters blood and removes old red blood cells while also serving as a site for immune responses against blood-borne pathogens.
- Lymph Nodes – Act as filters for lymphatic fluid and are sites where immune responses to pathogens occur.
- Tonsils, Appendix, Peyer’s Patches (in intestines) – Contain immune cells that help detect and respond to pathogens.
Since bone marrow and thymus are responsible for the production and maturation of lymphocytes, they are considered primary lymphoid organs, making option C (Bone marrow and thymus) the correct answer.