Normal shape and size of the red blood cells are biconcave discs,having 7.8 micrometers and a thickness of 2.5 micrometers at the thickest point and 1 micrometer or less in the center.The average volume of the red blood cell is 90 to 95 cubic micrometers. Production of red blood cells: In the early weeks of embryonic life,primitive,neucleated red blood cells are produced in the yolk sac.

During the middle trimester of gestation,the liver is the main organ for production of the red blood cells but reasonable numbers are produced in the spleen and lymph nodes.After birth red blood cells are produced exclusively in the bone marrow. Genesis of red blood cells:

The red blood cells begin their lives in the bone marrow from a single type of cell called plueripotent hematopoetic stem cell,from which all the cells of the circulating blood are eventually derived.

Stages of differentiation of red blood cells: The first cell that can be identified as belonging to the red blood cell series is the proerythroblast.Then it divides multiple times,eventually forming many mature red blood cells. The first generation cells are called basophil erythroblast.

The cells at this time has accumulate very little heamoglobin.,the nucleus condenses to a small size and its final remnant is absorbed or extruded from the cell. At this time,the endoplasmic reticulum is also absorbed.The cell at this stage is called a reticulocyte .

During this reticulocyte stage,the cells pass from the bone marrow into the blood cappillaries by diapedesis.The remaining besophilic material in the reticulocyte normally disappeas within 1 to 2 days and the cell is then mature erythrocyte.

The total mass of red blood cells in the circulatory system is regulated within marrow limits.so adequate red cells are always available to provide sufficient transport of oxygen from the lungs to to the tissue. Maturation of red blood cells: Especially important for final maturation of the red blood cells are two vitamins,vitamin B12 and folic acid. Both of these are essential for the synthesis of DNA . Life span of red blood cells: When red blood cells are delivered from the bone marrow into the circulatory system,they normally circulate an average of 120 days before being destroyed.