Hemopoiesis is the process by which blood cells are produced in the body, primarily occurring in the bone marrow.
Hematopoietic stem cells (HSCs) differentiate into various blood cell types, including erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets).
1) Erythropoiesis
Production of erythrocytes (red blood cells) responsible for oxygen transport.
Process:
Begins with HSCs differentiating into proerythroblasts.
Under the influence of erythropoietin (EPO), proerythroblasts develop through several stages:
Proerythroblast → Basophilic erythroblast → Polychromatophilic erythroblast → Orthochromatophilic erythroblast → Reticulocyte.
Reticulocytes enter the bloodstream and mature into erythrocytes.
2) Leukopoiesis
Production of leukocytes (white blood cells) for immune defense.
Process:
HSCs differentiate into myeloid or lymphoid progenitor cells.
Myeloid progenitor cells develop into granulocytes (neutrophils, eosinophils, basophils) and monocytes.
Lymphoid progenitor cells develop into B and T lymphocytes and natural killer (NK) cells.
Regulated by cytokines and growth factors like GM-CSF, G-CSF, and interleukins.
3) Thrombopoiesis
Production of thrombocytes (platelets) for blood clotting.
Process:
HSCs differentiate into megakaryocyte progenitor cells.
Under the influence of thrombopoietin (TPO), these progenitors mature into megakaryocytes.
Megakaryocytes extend proplatelets into bone marrow blood vessels, which fragment into platelets released into the bloodstream.