HEMATOPOIESIS

What is hematopoiesis?

The process of forming the figurative elements of blood: proliferation, differentiation, and passage into circulation.

What are the main types of blood cell formation included in hematopoiesis?

Erythropoiesis (RBCs), leukopoiesis (WBCs), and thrombocytopoiesis (platelets).

What are the components of hematogenous red marrow?

Stem hematopoietic cells (30-70\%),

reticulo-vascular stroma,

adipose tissue,

fibrocytes,

extracellular tissue,

and vascular sinusoids.

What are the 3 main groups of hematopoietic cells?

Pluripotent stem cells,

progenitor hematopoietic cells,

and blood cell lineage.

What are the 3 compartments of hematopoiesis?

• Generation compartment (immature elements in red marrow) – 5–7 days

• Circulating compartment (mature RBCs, few reticulocytes) – 100–120 days

• Destruction compartment (aged RBCs) – spleen, liver, bone marrow

What are the main cell types in erythropoiesis evolution?

Stage	Main Features	What Happens
1. CSP (Pluripotent Stem Cell)	Primitive stem cell in red bone marrow	Can become any blood cell line (RBC, WBC, platelet). Has receptors for erythropoietin.
2. BFU-E (Burst-Forming Unit–Erythroid)	Early erythroid progenitor cell	Begins committing to the RBC line; rapid “burst-like” cell division.
3. CFU-E (Colony-Forming Unit–Erythroid)	Late erythroid progenitor	Highly sensitive to erythropoietin; prepares to form proerythroblasts.
4. Proerythroblast	Large nucleated cell	Starts hemoglobin and enzyme synthesis; can still divide; nucleus large and central.
5. Basophilic Erythroblast	Strongly basophilic cytoplasm (blue)	Intense RNA activity for hemoglobin synthesis; smaller nucleus.
6. Polychromatophilic Erythroblast	Cytoplasm both blue and pink	Ongoing hemoglobin accumulation gives mixed color; nucleus shrinks.
7. Oxyphilic (Normoblast)	Cytoplasm pink; nucleus very small	Hemoglobin nearly complete; nucleus expelled at the end of this stage.
8. Reticulocyte	No nucleus; residual ribosomal network	Enters circulation; finishes hemoglobin synthesis; matures in 1–2 days.
9. Erythrocyte (Mature RBC)	Biconcave, flexible, no nucleus or organelles	Fully functional red blood cell; circulates for ~120 days.

What are characteristics of the proerythroblast?

• Has erythropoietin receptors-

• Can proliferate and differentiate- Synthesizes Hb and enzymes- Nucleated

What happens during erythrocyte maturation?

• Reduction in size-

• Increase in cytoplasmic volume-

• Decreased basophilia-

• Nucleus reduction and expulsion

What is the total duration of evolution from CSP to reticulocyte?

5-7 days