First I would like to explain Hematopoiesis
Haematopoiesis (from Ancient Greek: haima blood; poiesis to make) (or hematopoiesis in the United States; sometimes also haemopoiesis or hemopoiesis)
It is the formation of blood cellular components.
It is the process of blood cell production, differentiation, and development.
Origin of Blood Cells
In developing embryos, blood formation occurs in aggregates of blood cells in the yolk sac, called blood islands. The first blood cells are primitive red blood cells (erythroblasts) formed during the first 2 to 8 weeks of life.
By the 2nd month of gestation, as development progresses, blood formation occurs in the spleen, liver and lymph nodes. The granular types of leukocytes have made their initial appearance. The liver predominates from about the 2nd to 5th months of fetal life.
In the 4th month of gestation, the bone marrow begins to function in the production of blood cells.
After the 5th fetal month, the bone marrow begins to assume its ultimate role as the primary site of hematopoiesis (medullary hematopoiesis).
The term erythropoiesis (erythro = RBC, and poiesis = to make) is used to describe the process of RBC formation or production.
In humans, erythropoiesis occurs almost exclusively in the red bone marrow.
Life cycle of a red blood cell
a) Kidneys respond to a lower than normal oxygen concentration in the blood by releasing the hormone erythropoietin.
b) Erythropoietin travels to the red bone marrow and stimulates an increase in the production of red blood cells (RBCs).
c) The red bone marrow manufactures RBCs from stem cells that live inside the marrow.
d) RBCs squeeze through blood vessel membranes to enter the circulation.
e) The heart and lungs work to supply continuous movement and oxygenation of RBCs.
f) Damaged or old RBCs are destroyed primarily by the spleen.