Erythrocyte (Red blood corpuscles) are highly differentiated and specialized for the function of transporting oxygen. In the lower vertebrates, the erythrocyte is nucleated but in mammals, it loses it nucleus, Golgi apparatus, mitochondria and centroiles before entering blood stream.
The erythrocytes are acidophilic biconcave discs and round in all mammals except in camel and llama where they are elliptical. (Birds, reptiles and fishes have elliptical nucleated erythrocytes). On surface view, the erythrocyte is circular in outline and the central depression appears as a lighter area depending on the focus.
Histologically, the erythrocytes appear entirely homogenous. The covering is a delicate plasma membrane formed by a condensation of the lipo-protein complex of the corpuscular substance. The contents of the corpuscle are present as a relatively fluid colloidal mixture.
- Chemically the erythrocyte consists of a protein and lipoid colloidal complex, of which the most important element is hemoglobin. Hemoglobin is the pigment which gives the red colour to the erythrocytes.
- The average diameter of the erythrocyte is as follows in microns: Elephant 9.0; man 7.3; rabbit 6.5; cow 6.1; cat 6.0; horse 5.7; sheep 5.0; goat 3.7; musk ox 2.5.
- Number (in millions per cubic m.m.) Goat 17.3, Sheep 11.5, cat 7.2, Horse 7, Dog 6.1, Ox 6, Man 5; Guinea pig 5; Rabbit 4.6, Chicken 2.9.
- The number, the size and shape of the erythrocytes are correlated to the metabolic activity of the different animal groups. High metabolic activity is correlated with small size and circular shape and large number of cells conversely, lower metabolic rate is correlated with larger size and small number of cells.
