Hematopoiesis is complex biological process by which body produce all cellular components of blood. Healthy adult produces approximately 100 billion to 400 billion new blood cells every single day.
Hematopoietic Stem Cells (HSCs)
All blood cells originate from a single type of unspecialized cell called Hematopoietic Stem Cell (HSC). They found primarily in bone marrow of adults, these cells possess two unique properties:
- Self-Renewal: They divide cells to produce more stem cells, ensuring cells never runs out.
- Multipotency: These cells can divide into any type of blood cell depending on body’s immediate needs.
As an HSC begins to develop, it chooses two primary paths,
Myeloid Lineage
Common myeloid progenitor is the ancestor of most of cells involved in innate immunity and oxygen transport.
This path produces:
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Erythrocytes (Red Blood Cells): Carry oxygen via hemoglobin.
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Megakaryocytes: Large cells that fragment to create Platelets for blood clotting.
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Mast Cells & Granulocytes: Including Neutrophils, Eosinophils, and Basophils, which act as body’s first responders to infection.
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Monocytes: Which mature into Macrophages to “eat” cellular debris and pathogens.
Lymphoid Lineage
Common Lymphoid Progenitor focuses on the adaptive immune system, the part of your body that remembers specific viruses and bacteria.
This path produces:
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B-Lymphocytes: Create antibodies.
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T-Lymphocytes: Directly kill infected cells or coordinate the immune response.
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Natural Killer (NK) Cells: Target tumors and virally infected cells.
Where Does It Happen?
| Life Stage | Primary Site of Hematopoiesis |
| Embryo (Early) | Yolk Sac |
| Fetus (2nd Trimester) | Liver and Spleen |
| Infant/Adult | Bone Marrow (primarily in the pelvis, sternum, and vertebrae) |
In cases of severe bone marrow disease, liver and spleen can sometimes resume blood cell production, known as extramedullary hematopoiesis.
4. Regulation and Balance
The body regulates hematopoiesis through hormones. For example, if your kidneys detect low oxygen levels, they release a hormone called Erythropoietin (EPO). This hormone travels to the bone marrow and signals the stem cells to ramp up production of Red Blood Cells.
Similarly, during an infection, Colony Stimulating Factors (CSFs) trigger the rapid production of White Blood Cells to fight off the invader
Why It Matters
Hematopoiesis is critical for treating medical conditions such as:
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Leukemia: A cancer where the marrow produces abnormal white blood cells.
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Anemia: A deficiency in red blood cell production.
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Bone Marrow Transplants: A procedure where healthy HSCs are infused into a patient to reboot their blood-making system.