Functions of Plasma Proteins

The proteins of the plasma serve several important functions.

1. They exert osmotic pressure varying from 25 to 30 mm Hg, which regulates blood volume, plasma water content and interstitial water content.
2. They give viscosity to the blood and thus aid to some degree in the maintenance of the blood pressure.
3. They act as carrier molecules for some hormones, vitamins and iron.
4. They act as buffers.
5. The fibrinogen plays an essential role in coagulation of the blood.
6. The gamma fraction of the serum globulin (gamma globulin) is associated with production of immune bodies called antibodies. The concentration of these proteins increases during immunisation.

Most of the organic constituents of the plasma other than protein represent waste products of metabolism (e.g. urea, uric acid etc.) together with nutritive materials (e.g. amino acids, glucose and fats) absorbed from the intestinal tract. Of the inorganic constituents of plasma, sodium chloride is in highest concentration. Plasma also contains potassium, calcium, magnesium, sodium bicarbonate and minute amounts of iodine and iron. Phosphorus is present in both inorganic and organic forms. The concentration of inorganic phosphorus is about 3 mg and that of the organic form about 40 mg per 100 ml of blood. Potassium is in relatively high concentration in the cells of the blood and in the cells of the solid tissues but is in low concentration in the plasma and the body fluids generally.