Correct Option
(B) Lymphocytes, which are crucial components of the adaptive immune system, are primarily formed in the bone marrow. The bone marrow, particularly found within long bones, is the primary lymphoid organ where hematopoietic stem cells differentiate into various blood cells, including all lymphocytes. Both B lymphocytes mature in the bone marrow, and T lymphocyte precursors originate there before migrating to the thymus for maturation.
Incorrect Options
- (A) Liver: The liver is a vital organ involved in metabolism, detoxification, and protein synthesis. While it possesses immune functions and can contain lymphocytes, it is not the primary site for their formation in adults.
- (C) Pancreas: The pancreas is an endocrine and exocrine gland. Its exocrine function involves producing digestive enzymes, and its endocrine function involves secreting hormones like insulin and glucagon for blood sugar regulation. It has no role in lymphocyte formation.
- (D) Spleen: The spleen is a secondary lymphoid organ that filters blood, stores lymphocytes, and plays a significant role in immune responses by identifying and responding to pathogens. However, it is not involved in the primary formation (hematopoiesis) of lymphocytes.