(RBCs) (Gk. erythros-red, kytos-cell)-
Erythrocytes are circular, biconcave, non-nucleated cells (nucleated in camels). The size is about 7 μm in diameter and 2.5 μm in thickness. There are about 5.1 to 5.8 million RBCs per cubic mm of blood in adult male and 4.3 to 5.2 million per cubic mm in adult female. This is called total RBC count. The average life span is about 120 days.
Formation of RBCs is called erythropoiesis. In foetus, it occurs in liver and spleen whereas in adults it occurs in red bone marrow. The old and worn out RBCs are destroyed in liver and spleen. Increase in number of RBCs is called polycythemia whereas decreases in their number is called erythrocytopenia.
The cytoplasm of RBCs contains respiratory pigment called haemoglobin which helps in transport of oxygen and carbon dioxide. The normal harmoglobin content in adult male is 13-18 gm /100ml of blood and 11.5-16.5 gm/100ml of blood in adult female. Less amount of haemoglobin leads anaemia.
RBCs transport oxygen from lungs to tissues and carbon dioxide from tissues to lungs. They maintain blood pH as haemoglobin acts as a buffer. They also maintain the viscosity of blood.