Definition
Erythropoiesis is the process of the origin, development and
maturation of erythrocytes
Hemopoiesis or Hematopoiesis
It is the process of origin, development and maturation of all
the blood cells
Sites of Erythropoiesis
Fetal stage: yolk sack, liver, spleen, lymphoid tissue
Newborns & Children: long and flat bones
Adults: Membranous bones like vertebra, sternum, skull
Process of Erythropoiesis
From Hemopoietic stem cells: also called uncommitted
pluripotent hemopoietic stem cells (PHSC): primitive cells in the bone marrow which
gives rise to all types of blood cells
When the cells are designed to form a particular type of
blood cell, the uncommitted PHSCs are called committed PHSCs, which is restricted
to give rise to one group of blood cells
Committed PHSCs are of 2 types:
- Lymphoid stem cells: gives rise to lymphocytes & natural killer (NK) cells
- Colony forming cells: which gives rise to myeloid cells
Colony forming myeloid cells are of 3 types:
- Colony forming unit-erythrocytes (CFU-E) – develops into erythrocytes
- Colony forming unit-granulocytes/monocytes (CFU- GM) – develops into granulocytes and monocytes
- Colony forming unit-megakaryocytes (CFU-M) – develops into platelets
Changes during Erythropoiesis
Colony forming unit-erythrocytes (CFU-E) pass through different stages and finally become the matured
RBCs
During these stages 4 important changes occur
- Reduction in size of the cell (from 25 to 7.2 µ)
- Disappearance of nucleoli and nucleus
- Appearance of hemoglobin
- Change in the staining properties of the cytoplasm
Stages of Erythropoiesis
- Proerythroblast
- Early normoblast
- Intermediate normoblast
- Late normoblast
- Reticulocyte
- Matured erythrocyte
Duration of Erythropoiesis:
- Proerythrblast to Reticulocyte: 5 days
- Reticulocyte to Matured RBC: 2 days
- Total: 7 days
Proerythroblast (Megaloblast)
- First cell derived from CFU-E
- Size: Large with a diameter of 20µ
- Nucleus: Large, occupying the cell completely
- Haemoglobin: Not present
- Cytoplasm: Basophilic in nature
Early normoblast
- Cell derived from multiplication of proeythroblast
- Size: Little smaller with a diameter of 15µ
- Nucleus: Condensation of chromatin
- Haemoglobin: Starts synthesis
- Cytoplasm: Basophilic in nature
Intermediate normoblast
- Cell derived from early normoblast
- Size: Smaller with a diameter of 10-12µ
- Nucleus: Further condensation of chromatin
- Haemoglobin: Starts appearing
- Cytoplasm: Both Acidophilic & Basophilic in nature
Late normoblast
- Cell derived from intermediate normoblast
- Size: Much smaller with a diameter of 8-10µ
- Nucleus: More condensation of chromatin, small in size
- Haemoglobin: Present
- Cytoplasm: Acidophilic in nature
Reticulocyte
- Cell derived from late normoblast
- Size: Slightly larger than mature RBCs
- Nucleus: Disappears, only network of reticulum
- Haemoglobin: Present
- Cytoplasm: Basophilic in nature
Matured Erythrocyte
- Cell derived from Reticulocyte
- Size: 7.2µ
- Nucleus: Not present
- Haemoglobin: Present
- Cytoplasm: Contains Hb
- Shape: Biconcave
Factors necessary for Erythropoiesis
- General factors
- Maturation factors
- Factors necessary for hemoglobin formation
General Factors
- Erythropoietin
- Thyroxine
- Hemopoietic growth factors
- Vitamins
Erythropoietin
Secreted by peritubular capillaries of kidney, little quantities by liver
and brain
Hypoxia is the stimulant for the secretion of Erythropoietin
Actions of erythropoietin
- Promotes production of proerythroblasts from CFU-E
- Development of proerythroblasts into matured RBCs
- Release of matured erythrocytes into blood
Thyroxine
Secreted by thyroid gland
Thyroxine accelerates the process of erythropoiesis
Hyperthyroidism secretes excess of Thyroxine leading to Polycythemia
Hemopoietic
growth factor
They are interleukins which induce the proliferation of PHSCs
Interleukins involved are
- Interleukin-3 (IL-3) & secreted by T-cells
- Interleukin-6 (IL-6) secreted by T-cells, endothelial cells and macrophages
- Interleukin-11 (IL-11) secreted by osteoblast
Vitamins
- Deficiency of these vitamins cause anaemia associated with other disorders
- Vitamin B deficiency causes anaemia and pellagra
- Vitamin C causes anaemia and scurvy
- Vitamin D deficiency causes anaemia and rickets
- Vitamin E deficiency leads to anaemia and malnutrition
Maturation Factors
- Vitamin B12 (Cyanocobalamin)
- Intrinsic Factor of Castle
- Folic Acid
Vitamin B12
(Cyanocobalamin)
- It is called extrinsic factor since it is obtained from diet
- Its absorption from intestine requires the presence of intrinsic factor of Castle
- It is stored mostly in liver and in small quantity in muscle
- It is essential for synthesis of DNA in RBCs
- Its deficiency leads to failure in maturation of the cell and reduction in the cell division
- Deficiency of vitamin B12 causes Pernicious Anaemia
Intrinsic factor
of Castle
- It is produced in gastric mucosa by parietal cells of gastric glands
- It is essential for the absorption of vitamin B12 from
- intestine, failure of which leads to Pernicious Anaemia
- Deficiency of intrinsic factor occurs in Severe gastritis
- Ulcer
- Gastrectomy
Folic Acid
- It is required for the synthesis of DNA
- In its absence the synthesis of DNA decreases causing failure of maturation of cells
- This leads to anaemia in which the cells are cause Magaloblastic Anaemia
Factors necessary for Hemoglobin formation
They are essential for the formation of hemoglobin in the RBCs, deficiency of which leads to anaemia
The factors are
- First class proteins and amino acids: Globin
- Iron: For Heme part of Hb
- Copper: For absorption of iron from intestine
- Cobalt and nickel: For utilization of iron during Hb
- formation
- Vitamins: Vitamin C, riboflavin, nicotinic acid and pyridoxine are necessary for formation of Hb
Summary
Erythropoiesis is the process of the origin, development and maturation of erythrocytes
Uncommitted PHSCs → committed PHSCs
Committed PHSCs → CFU-E (Colony Forming Unit Erythrocyte)
CFU-E → Proerythroblast → Early normoblast → Intermediate normoblast → Late normoblast → Reticulocyte → Matured RBC
Duration 7 days
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