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 :
The correct answer is: Bone marrow and thymus
Explanation:
The lymphoid organs are classified into two main categories: primary (or central) lymphoid organs and secondary (or peripheral) lymphoid organs.
Primary Lymphoid Organs:
These are the sites where lymphocytes (B cells and T cells) are produced and mature. The two primary lymphoid organs in humans are:
- Bone Marrow:
- It is the site of hematopoiesis, where all blood cells, including lymphocytes, are generated.
- B cells mature in the bone marrow before migrating to secondary lymphoid organs.
- Thymus:
- It is responsible for T cell maturation.
- Immature T cells migrate from the bone marrow to the thymus, where they undergo selection processes to ensure self-tolerance and functionality before being released into circulation.
Secondary Lymphoid Organs:
These are the sites where lymphocytes encounter antigens, become activated, proliferate, and initiate immune responses. Examples include:
- Lymph nodes: Filter lymph and trap pathogens.
- Spleen: Filters blood and responds to systemic infections.
- Tonsils, Appendix, and Peyer’s Patches (GALT): These are mucosa-associated lymphoid tissues (MALT) that provide immune surveillance at mucosal surfaces.
Since bone marrow and thymus are the organs responsible for lymphocyte production and maturation, they are classified as primary lymphoid organs, making them the correct answer.