Erythrocytes are nucleated in all vertebrates except mammals and contain haemoglobin in the cytoplasm, in lower vertebrates (fish, Amphibia, reptiles and birds) these are oval or lentil in shape but in mammals these are biconcave discs with an average diameter of 6-9 microns.
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These cells are produced in the red bone marrow of bones such as the ribs, vertebrate and-skull.
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The red cells or erythrocytes during their development are large colourless and have larges nuclei.
Normally by the time, they are to be released into the blood stream they have lost the nuclei and have accumulated haemoglobin that is why they are technically corpuscles and not cells.
The average span of these cells is 20-126 days after this time they are removed by the liver and the spleen where globin part of these cells is converted to the protein end product, urea.
The liver and spleen extract the iron and conserve most of it for making more red blood cells or corpuscles.
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The dye is converted to red pigment called bilivcrdin and is excreted from the body in the bile which the liver manufactures and sends down to the intestine via the bile ducts.
At the same time certain valuable substances are released into the blood streams which are used in the manufacturing of the new blood red cells.
The production of red cells or corpuscles requires an intake of food which provides sufficient amounts of amino-acids iron and traces of copper.
Two vitamins of the B-complex participate in the formation of RBC—folic acid and vitamin Bu. Vitamin C is necessary to convert folic acid to its active form.
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The presence of antigens A, B and the Rh factor in the red blood cells accounts for blood types.
The individual blood cells are pale yellowish in colour but when they are aggregated they appear to be reddish in colour.
The red colour of the blood is entirely due to the presence of haemoglobin in the cells. Haemoglobin is a complex protein made up of 95% globin and 5% haematin, it is commonly known as respiratory pigment.
Venous blood is purplish red and arterial blood is bright scarlet. The variation in colour of blood is due to the difference in amounts of oxygen absorbed by the haemoglobin in the two cases.
Each red cell is enveloped externally by a thin membrane which is composed of lecithin and cholesterol.
Inside the cell there is a elastic substance called stroma, in the meshes of which iron pigment haemoglobin is present.
The blood of woman contains an average of about 5 million red cells per cubic millimeter, while in man about 5. 5 million per cubic millimeter.