Hematopoiesis (blood cell formation)

Formation of red blood cells

Since RBCs are anucleate, they are unable to divide, grow, or synthesize proteins RBCs wear out in 100 to 120 days When worn out, RBCs are eliminated by phagocytes in the spleen or liver Lost cells are replaced by division of hemocytoblasts in the red bone marrow

Hemocytoblast

All blood cells are derived from a common stem cell

Formation of White Blood Cells and Platelets

Controlled by hormones Colony stimulating factors (CSFs) and interleukins prompt bone marrow to generate leukocytes Thrombopoietin stimulates production of platelets

Hemocytoblast differentiation

Lymphoid stem cell produces lymphocytes Myeloid stem cell produces all other formed elements

Hematopoiesis

Process of blood cell formation, occurs in red bone marrow

Control of Erythrocyte Production

Rate of RBC production is controlled by a hormone called erythropoietin Kidneys produce most erythropoietin as a response to reduced oxygen levels in the blood Homeostasis is maintained by negative feedback from blood oxygen levels