Erythrocytes or red blood cells:

1. These are otherwise called Red Blood cells or corpuscles.
2. These are the most numerous cells in the blood.There are about 4.5 to 5.5x 10⁹ cells per ml of blood.
3. Each red blood cell is circular and biconcave in its shape.
4. Immature red blood cells have all the organelles. After maturation, organelles like nucleus, mitochondria, lysosomes, Golgi complex, endoplasmic reticulum, ribosomes etc., disappear in R.B.C. Therefore mature red blood cells have only plasma membrane and cytoplasm.
5. In adults, red blood cells are formed only in the marrow of long bones while in embryonic stages they are formed in the liver and spleen.
6. Red blood cells live for 120 days in the blood.
7. The old red blood cells are destroyed mostly in spleen and to some extent in liver.
8. Every day about 10*10¹² red blood cells are destroyed and the same number of new red blood cells are added to the blood.