Red Blood Cells (Erythrocytes):

These are the most numerous blood cells.

Amount of Red Blood Cells:

A cubic millimeter of blood contains 5 to 5.5 million of them in males and 4 to 4.5 million in females. These cells, when formed, have a nucleus.

Structure of Red Blood Cells (Erythrocytes):

In the RBCs of mammals, the nucleus, mitochondria, endoplasmic reticulum, etc, are lost when they get mature and before they enter the blood. About 95% of the cytoplasm of red blood cells is filled with hemoglobin, which transports O₂ and small amounts of CO₂. The remaining 5% consists of enzymes, salts, and other proteins. These cells once mature, do not divide. RBCs are biconcave and have an elastic cell membrane.

Size of Red Blood Cells:

The average diameter of erythrocytes is 08 µm.

Formation of Red Blood Cells:

In the embryonic and fetal life, they are formed in the liver and spleen. In adults, they are formed principally in the red bone marrow of short and flat bones, such as the sternum, ribs, and vertebrae.

The average life span of a red blood cell:

The average life span of a red blood cell is about four months (120 days) after which it breaks down in the liver and spleen by phagocytosis.