Define erythropoiesis. Explain the site, duration, steps of erythropoiesis, and factors affecting it.

 ERYTHROPOIESIS

 * Refers to the process of production and maturation of Red Blood

 Cells (erythrocytes)

 * Site of production – Red bone marrow of all the bones upto 20

 years of life. After 20 years, only flat bones produce RBCs.

Stages of Erythropoiesis :

1. Hemocytoblast

2. BFU –E, Blast Forming Unit – E

3. CFU-E, Colony Forming Unit – E

4. Proerythroblast

5. Early normoblast

6. Intermediate normoblast

7. Late normoblast

8. Recticulocyte

9. Mature erythrocyte

1. Hemocytoblast:

 - 18 – 23 um in diameter

 - Large Nucleus

 - Thin rim of basophilic cytoplasm

 -

Pleuripotent stem cells

2. Blast Forming Unit – E:

 - Unipotent progenitor cell.

 - Less Sensitive to Erythropoietin

3. CFU (E) – Colony Forming Unit

 - Matured unipotent progenitor cell

 - Highly sensitive to erythropoietin

4. Proerythroblast:

 - 14-19 µm in diameter.

 - Large nucleus with distinct nucleoli

 - Basophilic cytoplasm.

 - Vit B12 & Folic acid are required for the conversion of this stage into next stage.

5. Early normoblast;

 - 11-17 µm in diameter.

 - Dense nucleus

 - Basophilic cytoplasm.

6. Intermediate normoblast:

 - 10-12 µm in diameter

 - more condensed nucleus

 - Hb (Hemoglobin) is formed

 - Polychromatophilic cytoplasm.

7. Late normoblast:

 - 8-12 µm in diameter.

 - Dense nucleus (Pyknotic)

 - Nucleus extrudes after this stage & disintegrates

 - Acidophilic cytoplasm.

8. Reticulocyte:

 - Almost of the same size of matured RBC

 - A small reticulum is seen in the cytoplasm.

10. Mature Erythrocyte:

 - About 7.2 um in diameter.

- No nucleus

- Acidophilic cytoplasm 

Regulation of Erythropoiesis

1. Erythropoietin a hormone secreted by kidneys

 - Stimulates the bone marrow tissue to produce more RBCs.

2. Hypoxia: Lack of O2 is the main condition which stimulates erythropoietin secretion.

 Lack of O2 (Hypoxia)

 Kidneys

 Erythropoietin

 Red Bone marrow

 RBC Production

 Restoration of O2 Supply 

3. Nutrients:

a) Proteins for synthesis of Hb.

b) Minerals:

i) Iron : for synthesis of heme part of Hb.

ii) Copper: for synthesis of Hb.

4. Vitamins:

a) Vitamins B12 & Folic Acid: Required for synthesis of DNA. These factors are called

 maturation factors.

b) Vitamin C is also required.

5. Hormones:

 Thyroxine stimulate erythropoietin

 Glucocorticoids

 Testosterone

 Growth hormone RBC Production

Normal Count of RBC:

 - Male 5-6 million/cu mm of blood

 - Female 4.5 – 5.5 millions/cu mm of blood.