Anatomy And Physiology

Anatomy Physiology

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Platelets (thrombocytes) are irregularly shaped colorless corpuscles that circulate in the blood. The function of platelets is to prevent bleeding (hemostasis). Each platelet contains within them, compounds that enable them to stick to each other and to a damaged vessel wall. When a vessel gets injured, platelets gather together to form a clot (thrombus) at the site of the injury. Excessive bleeding can occur when the number of platelets is too low; however, too many platelets can lead to thrombosis.

What are platelets?

Platelets are produced in the bone marrow from cells called megakaryocytes. Platelets are cell fragments that do not have a nucleus containing DNA; therefore, they do not go through the process of mitosis. Platelets contain proteins that enable them to stick to damaged sites inside blood vessel walls. They also contain dense granules that secrete other proteins essential for creating firm plugs around blood vessel breaks.

Function of platelets:

The wall of a vessel is lined by cells called endothelium. When the endothelium lining of a blood vessel is disrupted by injury, the blood and extra vascular compartments react to produce a coagulation response. Platelets adhere to the collagen fibers exposed at the region of vascular damage, forming a platelet plug which soon coagulates by the adhesion of fibrin strands interlocking the platelets. Platelet adhesion at the site of blood vessel wall damage initiates activation events that lead to platelet aggregation.

After activation, platelets become more spherical with extended long filaments, increasing the area of surface contact. At this stage, platelets secrete alpha and dense granules, including serotonin, thromboxane A2, and ADP, into the surrounding area, providing a high concentration of molecules needed for platelet plug formation at the wounded site. Platelet aggregation is promoted by ADP and thromboxane A2 (TxA2).

Vessel repair is performed by the secretion of chemicals by the aggregated platelets. The release of fibrin (blood clotting factor) produces a series of tiny threads that begin to trap other blood cells within it, producing a blood clot. This blood clot is later dissolved by an enzyme known as plasmin, and the mesh of platelets is cleared up by other cells known as phagocytes in a process known as phagocytosis.

Either too few (thrombocytopenia) or too many platelets  (thrombocytosis) can bring about serious health problems. A small platelet count in the blood can increase the risk of bleeding. A high platelet count in the blood augments the risk of developing blood clots in the blood vessels (thrombosis), restricting the flow of blood and causing a stroke or a heart attack. According to, The normal platelet count in a healthy individual is between 150,000 and 450,000 per micro liter. The average lifespan of a platelet ranges from 5 to 9 days.

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