Which statement correctly describes erythropoiesis?

• A. It begins in the liver
• B. It is the production of platelets
• C. It occurs exclusively in the spleen
• D. It is the production of red blood cells beginning in the red bone marrow and regulated by EPO from the kidney

Answer: (D)

Erythropoiesis is the production of red blood cells, and in adults it begins in the red bone marrow where progenitor cells differentiate and mature into circulating RBCs through stages that culminate in reticulocytes. This process is tightly regulated by erythropoietin, a hormone produced by the kidney in response to low oxygen levels (hypoxia). When the kidneys sense hypoxia, they release erythropoietin, which stimulates the bone marrow to increase RBC production, boosting the body’s capacity to carry oxygen.

Understanding this helps explain why the statement is correct: it accurately links the production site (red bone marrow) with the regulatory trigger (EPO from the kidney). The other ideas aren’t correct for normal erythropoiesis—liver is a major site during fetal development, not adult RBC production; platelets are produced through thrombopoiesis from megakaryocytes; and erythropoiesis is not restricted to the spleen, which can be involved only in special circumstances but is not the normal site.