The function of blood plasma:

Plasma is primarily water in which proteins, salts, ions, metabolites, and wastes are dissolved. Water constitutes about 90-92% of plasma, and 8-10% are dissolved substances.

Materials present in the water of plasma:

The materials present in the water of plasma can be divided into the following six categories.

1. The salts make up 0.9% of the plasma, by weight. More than two-thirds of this amount are sodium chloride (the table salt). Salts of bicarbonate are also present in considerable amounts. Ca, Mg, Cu, K and Zn are found in trace amounts. Changes in the concentration of a particular ion can create serious disturbances e.g. change in the pH of the blood. The normal pH of human blood is 7.4 and it is maintained within narrow limits. Any change in blood pH affects the reactions of the body.
2. Proteins constitute 7-9 % by weight of the plasma. Antibodies are produced by lymphocytes (a type of white blood cell), in response to antigens and then passed to plasma and lymph. They are a part of the body's immune system. Fibrinogen is a plasma protein that takes part in the blood clotting process. The protein prothrombin acts as a catalyst in the blood clotting process. Albumin proteins circulate in the blood and maintain the water balance of the blood. They do not let the water go out of their blood.
3. Organic nutrients in the blood include glucose, lipids, amino acids, etc. They enter the blood after being absorbed from the digestive system.
4. Plasma also contains nitrogenous waste products formed as a result of cellular metabolism. In cells, they are produced in the form of ammonia. Plasma carries ammonia to the liver where it is converted into different (less toxic) forms, which are then carried to the kidneys for removal.
5. Hormones, which work as an important part of the body's coordination system, are carried by blood plasma.
6. Respiratory gases CO₂ and O₂ are present in the plasma of the blood. O₂ is primarily carried by RBCs but small amounts of it are also carried as dissolved in plasma. Most of the CO₂ is carried by plasma.