🩸 *Hematopoiesis* 🩸 is the process by which the body produces *blood cells* from *hematopoietic stem cells (HSCs)*. This occurs primarily in the *bone marrow* (in adults) and the *liver and spleen* (during fetal development). 📲 *Stages of Hematopoiesis:* 1. *Hematopoietic Stem Cells (HSCs)* - Pluripotent (can differentiate into all blood cell types). - Reside in the bone marrow. - Can self-renew or differentiate into *myeloid* or *lymphoid* progenitor cells. 2. *Progenitor Cells (Commitment to Lineages)* - *Myeloid Progenitor* → Gives rise to: - *Erythrocytes (red blood cells, RBCs)* - *Platelets* (from megakaryocytes) - *Granulocytes* (neutrophils, eosinophils, basophils) - *Monocytes/macrophages* - *Lymphoid Progenitor* → Gives rise to: - *B cells, T cells, NK cells* 3. *Maturation & Release* - Mature cells enter the bloodstream. - RBCs carry oxygen, WBCs fight infection, platelets aid clotting. 📲 *Regulation of Hematopoiesis* - Controlled by *growth factors & cytokines*: - *Erythropoietin (EPO)* → Stimulates RBC production. - *Thrombopoietin (TPO)* → Stimulates platelet production. - *Granulocyte-Colony Stimulating Factor (G-CSF)* → Stimulates neutrophil production. - *Interleukins (e.g., IL-3, IL-7)*→ Support various lineages. 📲 *Clinical Relevance* - *Bone marrow failure* (e.g. aplastic anemia). - *Leukemia* (abnormal proliferation of blood cells). - *Hematopoietic stem cell transplantation (HSCT)* used to treat blood disorders.