Which structure in the body is primarily responsible for red blood cell synthesis?

The bone marrow is primarily responsible for the synthesis of red blood cells, a process known as erythropoiesis. This specialized tissue is located within the cavities of certain bones, particularly the long bones, pelvis, and ribs. It contains hematopoietic stem cells, which have the capability to differentiate into various types of blood cells, including red blood cells, white blood cells, and platelets.

The process of red blood cell production is stimulated by erythropoietin, a hormone produced by the kidneys in response to low oxygen levels in the blood. While the kidneys play a role in regulating red blood cell production, they do not synthesize the cells themselves. The liver and spleen are also involved in the lifecycle of blood cells, particularly in the storage and breakdown of red blood cells, but they do not actively produce them. Therefore, the bone marrow is the key site for red blood cell synthesis.