Physiology · Blood, hemostasis and basic immunity
Hematopoiesis !
- Concept
- Exam priority: medium
All blood cells come from a few stem cells in the bone marrow that copy themselves and mature into red cells, white cells and platelets.
Updated 2026-11-01
Also called: Blood cell formation, Hemopoiesis
See it in 3D: Hip bone · Sternum · Femur · Liver · Spleen · Thymus
What it is
Hematopoiesis is the continuous production of all blood cells from hematopoietic stem cells. These rare cells renew themselves and branch into a myeloid line (red cells, platelets, granulocytes, monocytes) and a lymphoid line (B, T and NK cells). Growth factors from the kidney, liver, marrow stroma and immune cells adjust each line to demand.
Key facts
- Marrow aspirates and biopsies are usually taken from the posterior iliac crest.
- With age, red marrow in long bones is replaced by yellow (fatty) marrow, which can reactivate under stress.
- Stem cells are identified by surface markers such as CD34, the basis of collecting them for transplantation.
Lines and their main growth factors
| Line | Final cell | Main factor | Source of the factor |
|---|---|---|---|
| Erythroid | Red cell | Erythropoietin | Kidney (renal cortex) |
| Megakaryocytic | Platelets | Thrombopoietin | Liver |
| Granulocytic | Neutrophil, eosinophil, basophil | G-CSF, GM-CSF, IL-5 (eosinophils) | Macrophages, endothelium, T cells |
| Monocytic | Monocyte → macrophage | M-CSF | Stroma, macrophages |
| Lymphoid | B, T and NK cells | IL-7 and others | Marrow stroma, thymus |
Clinical notes
- In β-thalassemia major, expanded marrow widens the skull and facial bones ('hair-on-end' X-ray) and the liver and spleen enlarge.
- Fanconi anemia: an inherited DNA-repair defect that leads to marrow failure of all lines (pancytopenia).
Test yourself
Think of the answer, then tap the question to see it.
Why does a child with severe β-thalassemia develop hepatosplenomegaly?
Ineffective erythropoiesis and anemia drive EPO very high; the liver and spleen, fetal sites of blood formation, resume hematopoiesis and the spleen also removes abnormal cells.
Which bone is the usual site for an adult bone marrow biopsy and why?
The posterior iliac crest: it holds active red marrow throughout adult life and is safe and easy to reach.
Where do T cells and B cells complete their maturation?
B cells mature in the bone marrow; T-cell precursors leave the marrow and mature in the thymus, where self-reactive cells are removed.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- Erythropoiesis and erythropoietin
- White blood cells: types and functions
- Primary hemostasis and platelets
- Innate and adaptive immunity: overview
Related conditions
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 18.2 Production of the Formed Elements (OpenStax (Rice University), 2022); 18.1 An Overview of Blood (OpenStax (Rice University), 2022); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 33). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.