Coagulation Of Blood | Function of Blood

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Coagulation Of Blood ( Blood Clotting )

• When an injury is caused to a blood vessel bleeding starts which is stopped by a process called blood clotting or blood coagulation.
• This process can be described under three major steps.

• First Step

• At the site of an injury, the blood platelets disintegrate and release a phospholipid, called platelet factor-3 (= Platelet throm- boplastin).
• Injured tissues also release a lipoprotein factor called thromboplastin.
• These two factors combine with calcium ions (Cat+) and certain proteins of the blood plasma to form an enzyme called prothrombinase.

• Second Step 

• prothrombinase inactivates heparin (or antiprothrombinanticoagulant) in the presence of calcium.
• Prothrombinase catalyzes breakdown of prothrombin (inactive plasma pro- tein) into an active protein called thrombin and some small peptide fragments.

• Third Step.

• Thrombin acts as enzyme and first brings about depolymerization of fibrinogen (a soluble plasma protein) into its monomers. Later thrombin stimulates repolymerization of these monomers into long insoluble fibre-like polymers called fibrin.
• The thin, long and solid fibres of fibrin form a dense network upon the wound and trap blood corpuscles (RBCS, WBCS and platelets) to form a clot.
• The clot seals the wound and stops bleeding. Soon after the clot starts contracting and a pale yellow fluid, the serum, starts oozing out.
• This serum is blood plasma minus fibrinogen and blood corpuscles.

• Vitamin K is essential for blood clotting as it is necessary for the synthesis of prothrom- bin in the liver.

Bleeding Time

• When a sharp knife is used to pierce the tip of the finger or lobe of the ear, bleeding ordinarily lasts 3 to 6 minutes.
• However, the time depends largely on the depth of the wound and other clotting factors.
• Lack of clotting factors can prolong the bleeding time.

Clotting Time

• Many methods have been devised for determining clotting times. The one most widely used is glass test tube method.
• By this method the normal clotting time is about 3 to 8 minutes.

• Recent theory of blood clotting is cascade theory proposed by Macferlane.
• According to this theory 13 factors are required for blood clotting. VI factor is hypothetical. Actually there is no factor VI.

Role of Vitamin K in Blood Clotting

• Vitamin K is essential for blood clotting because it is necessary for the synthesis of prothrombin in the liver.
• If vitamin K is not sufficient in the body, blood clotting becomes inefficient.

Functions of Blood

• On the basis of the above deseription, the general functions of blood can briefly be summarised as below.

• Transport of Food Materials. Blood transports the digested food from the alimen- tary canal to the different body cells. 
• Transport of Respiratory Gases. Oxygen is carried from the respiratory organs to the tissues and carbon dioxide from the tissue to the respiratory organs by blood.
• Transport of Hormones. Hormones are carried by blood from the endocrine glands to the places of use.
• Transport of Excretory Matter. Blood transports the excretory matter to the kid- neys or other excretory organs.
• Transport of Heat. Blood allows the transfer of heat from the deeper tissue to surface of the body where it can be lost.
• Defence against Infection. Some white blood corpuscles are phagocytic in action, however, certain white blood corpuscles produce antitoxins to neutralize the toxins released by the foreign germs.
• Temperature Regulation. Blood maintains the body temperature to a constant level after distributing heat within the body.
• Water Balance. Blood maintains water balance to a constant level by bringing about constant exchange of water between circulating blood.and tissue fluid.
• Maintenance of pH. Blood helps to regulate the pH of the body.
• Prevention of Excessive Loss of Blood. When any part of the body is injured, loss of blood is prevented by the formation of a clot.
• Helps in Healing. Blood maintains necessary supplies for the repair of damaged tissue. Eosinophils and basophils help in the healing of wounds.
• Maintenance of Physiological Co-operation. Blood maintains a physiological co- operation between parts of the body by circulating from one to other parts.

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