Hematopoietic growth factors are molecules that regulate the differentiation rate of hematopoietic stem cells (HSCs). Erythropoietin (EPO), primarily produced by the kidneys, plays a crucial role in erythrocyte production. When oxygen levels in the blood are low, EPO is released into the bloodstream, reaching the bone marrow, where it stimulates HSCs to differentiate and mature into erythrocytes, which are vital for oxygen transport.

Thrombopoietin (TPO), mainly released by the liver, stimulates the proliferation and maturation of megakaryocytes into platelets, which are essential for blood clotting and wound healing.

Cytokines, small signaling glycoproteins, play a vital role in hematopoiesis. Interleukins and colony-stimulating factors (CSFs) are two significant classes of cytokines that regulate the maturation of various blood cells. For example, granulocyte CSF promotes the growth and maturation of granular leukocytes. Interleukins target specific cell types; interleukin-2 stimulates T-cell proliferation, while interleukin-3 affects granulocytes, megakaryocytes, and erythroid precursors.