Where are red blood cells produced?

• A. Liver
• B. Stem cells in bone marrow
• C. Spleen
• D. Lymph nodes

Answer: (B)

Red blood cells are produced by hematopoietic stem cells in the bone marrow through erythropoiesis. In adults, this process happens in the red marrow of flat bones and the ends of long bones, where stem cells differentiate into erythroid precursors and eventually mature into red blood cells. Erythropoietin, mainly from the kidneys, stimulates production when oxygen levels are low.

The liver and spleen play a role during fetal development as primary sites of hematopoiesis and can resume producing blood cells in certain conditions (extramedullary hematopoiesis), but they are not the normal site of red blood cell production in healthy adults. Lymph nodes do not produce red blood cells.