Blood is probably the most vital fluid found in humans and other animals since it provides important nourishment to all body organs and tissues and carries away waste materials. It is not surprising that blood is sometimes referred to as "the river of life"; blood is pumped from the heart through a network of blood vessels collectively known as the circulatory system. When we accidentally cut ourselves, these blood vessels get damaged and the blood oozes out. If the vessels are not repaired, the blood will continue to escape from the body and cause serious problems. Fortunately, the body is all equipped to heal such situations and it is certainly quite an ingenious process!

The blood has many functions, one of which is the protection of the body. It has the ability to clot which helps to stop bleeding and thus prevent unwanted micro-organisms from entering the blood stream. Blood has about millions of different cells - it has the plasma, a colorless liquid in which we have

• red blood cells (they help in carrying oxygen around the body and are also known as erythrocytes)

• white blood cells (help in defending the body from diseases) and lastly

• the platelets, the smallest of the cells.

Although each of these three cells play a large role in helping the body function, we will mainly focus on the platelets since they are involved in blood clotting and help to stop bleeding.

About 250 million platelets are present in 1 milliliter of blood, so you can imagine how tiny they are! Their basic function is to make the blood clot, or coagulate, and discontinue bleeding. Studying how platelets function has become quite a hot topic with doctors, since the platelets might have some connection with the hardening of the arteries or arteriosclerosis.


How The Platelets Operate : In general, the walls of a blood vessel are lined with a smooth layer or pavement of epithelial cells. The moment the skin gets cut, this pavement is damaged and broken and all the constituents are exposed and come into contact with the other parts of the vessel wall. This contact makes the platelets stick to the wall and also to each other. This forms a type of barrier or plug that prevents further bleeding. The platelets allow release messengers into the blood carry out a number of functions like

• constricting the blood vessels to hamper the bleeding

• attracting more platelets to the damaged area to help enlarge the platelet plug and

• initiating the work of plasma-based clotting factors, such as fibrinogen and prothrombin.

Through a complex process involving many steps and the unity of many clotting factors, the plasma protein fibrinogen is transformed into long, sticky threads of fibrin. Together, the platelets and the fibrin create an intertwined meshwork that forms a strong, permanent clot. A clot is formed when the platelets, red and white blood cells become trapped within the fibers. This amazing wound healing process begins in just a few seconds of injury.

The following illustrations describe the process in more detail. The chart on the right shows that different symbols used for the various components present in blood.
When the skin gets a cut or wound, the blood vessels rupture, bleeding occurs and the platelets move towards the site to seal it	The tissue-clotting factors get released and the plasma factors also move to the site
Fibrin (a soft, mesh-like structure) is formed by the reaction of platelets, factors and other clotting agents	The platelets and blood cells trapped in the mesh secrete serum (blood without the clotting factors). This helps form the scab that prevents bacteria from entering the blood stream and causing infection.

The same process can be harmful if it takes place in undamaged blood vessels or even if clotting fails to take place, since as said earlier, this self-sealing aspect of the blood is vital for survival. With a little care, wound healing can achieved quickly.