1. Transport of oxygen and carbon dioxide:
Blood transports oxygen from the respiratory surfaces (lungs) to the tissues and carbon dioxide from the tissues to the respiratory surfaces and thus helps in respiration. Oxygen enters the blood through the lungs and carbon dioxide is eliminated from the blood mainly through the lungs.
2. Transport of food:
Blood carries soluble food from the intestines, first to the liver and then to the whole of the tissues where it is required for cellular activities.
The nutritive substances transported by the blood are glucose, amino acids, polypeptides, fats, vitamins, minerals and water.
3. Transport of waste products:
Waste products are being constantly produced by all the cells of the body. They are harmful to the body, therefore, they require immediate elimination.
Blood transports these wastes to the kidneys, lungs, skin and intestine so that they may be eliminated.
4. Chemical co-ordination:
Endocrine glands of the body produce hormones which are distributed by the blood to the vital tissues, and in various ways harmonize or co-ordinate the working of the body.
5. Maintenance of pH:
The plasma proteins of blood act as buffer system and thus prevent any shift in pH of the blood. This is because of amphoteric property of proteins.
6. Water balance:
Blood maintains water balance to a constant level by bringing about constant exchange of water between circulating blood and tissue field.
7. Transport of heat:
The blood allows the transfer of heat from the deeper tissues to the surface of the body where it can be lost.
8. Defence against infection:
Blood contains corpuscles which possess properties of phagocytosis and special products called antibodies which combat the bacteria and thus plays protective role after neutralizing their toxins.
9. Temperature regulation:
Blood maintains the body temperature to a constant level after distributing heat within the body.
Being under pressure in the arteries the blood helps to support the tissues.
11. Blood loss:
Blood prevents the excessive loss of blood in injury as it has the power of coagulation.