2.RBCs and erythropoiesis

Blood

1. Erythropoiesis Dr maria idrees; PT Dpt; TUF MS NMPT; RIPHA

2. Erythropoiesis is the process of the origin, development and maturation of erythrocytes Hemopoiesis or hematopoiesis is the process of origin, development and maturation of all the blood cells

3. Site of erythropoiesis In fetal life Occurs in three stages 1. Mesoblastic stage During first two months of intrauterine life RBCs produced from mesenchyme of yolk sac 2. Hepatic stage From third month of intrauterine life liver is the main organ that producesRBCs . Spleen and lymphoid organs also involved. 3. Myeloid stage Last three months RBCs produced from bone marrow and liver

4. In new born babies, children and adults RBCs are produced only from the red bone marrow. Upto age of 20 years, produced from red bone marrow of all bones After the age of 20 years, produced from membranous bones In adults liver and spleen may produce the blood cells if bone marrow is destroyed

5. Process of erythropoiesis Stem cells Stem cells are the primary cells capable of self renewal and differentiating into specialized cells. Hemopoietic stem cells in the bone marrow are called uncommitted pluripotent hemopoietic stem cells (PHSC). PHSC IS DEFINED as the cell that can give rise to all types of blood cells. But the best source of these cells is the umbilical cord blood.

6. When the cells are designed to form a particular type of blood cell, the uncommitted PHSCs are called committed PHSCs. Committed PHSC is defined as a cell, which is restricted to give rise to one group of blood cells.

7. CHANGES DURING ERYTHROPOIESIS Cells of CFU-E ( Colony Forming Unit-Erythroid ) pass through different stages and finally become the matured RBCs. During these stages four important changes are noticed. Reduction in size of the cell (from the diameter of 25 to 7.2 µ) 2. Disappearance of nucleoli and nucleus 3. Appearance of hemoglobin 4. Change in the staining properties of the cytoplasm.

8. STAGES OF ERYTHROPOIESIS Various stages between CFU-E cells and matured RBCs are: Proerythroblast 2. Early normoblast 3. Intermediate normoblast . 4. Late normoblast 5. Reticulocyte 6. Matured erythrocyte.

9. 1. Proerythroblast (megaloblast) First cell derived from CFU-E Large in size Large nucleus Nucleus has two or more nucleoli Does not contain hemoglobin Multiplies several times and finally formes cell of next stage called early monoblast Synthesis of hemoglobin starts

10. 2. Early normoblast Little smaller than proerythroblast Nucleoli disappears Condensation of chromatin network Also called basophilic erythroblast

11. 3. Intermediate normoblast Cell is smaller than early normoblast Nucleus still present Hemoglobin starts appearing Also called polychromophilic or polychromatic erythroblast

12. 4. Late normoblast Diameter of cell decreases further Nucleus becomes very small Quantity of hemoglobin increases Before it passes to the next stage, nucleus disappears called pyknosis

13. 5. Reticulocyte Known as immature RBC Slightly larger than matured RBC During this stage, cell enters the blood capillaries

14. 6. Matured erythrocytes Reticular network disappears and cell becomes matured RBC Biconcave shape With hemoglobin but without nucleus It requires 7 days for development and maturation of RBC from proerythroblast Requires 5 days upto the stage of reticulocyte Reticulocyte takes 2 days to become matured RBC