Platelets or thrombocytes are produced in the bone marrow and while not actually cells themselves are produced by cells called megakaryocytes. Platelets are formed by budding off of megakaryocytes and live on average for 5-9 days. They are small, colorless bodies, usually round or ovoidin shape. The average adult will produce 10ˆ11 platelets per day with the normal range of platelets being (150-400)x10ˆ9 platelets per liter of blood. Reserve platelets are stored in the spleen and released when needed.
Platelets are involved in vessel repair, platelet aggregation and promote vasoconstriction. In the bloodstream, platelets are an essential part of the clotting process. They function in the clotting process by acting as plugs around the wound and releasing certain factors that are needed for the formation of a blood clot. Platelets are also used to maintain the endothelial lining of the blood vessels.
So how does all this actually happen? Continue reading to find out.
The function of platelets is varied. When endothelial cells (the cells lining the interior of blood vessels) are damaged, such as getting a cut on your arm or leg, the platelets become exposed to the collagen in tissue. The contact causes the platelets to activate which results in platelet adherence to the damaged blood vessel. Fibronectin is secreted by both the endothelial cells and platelets and assists in the bonding process of the platelets to the collagen. Another factor, von Willebrand’s factor, acts as a glue to help with optimal platelet-collagen bonding. Once activated platelets take on another shape, becoming more spherical with long, irregular arms. This allows the platelets to cover a larger area and assists in the bonding process with other platelets and proteins necessary in the coagulation process. The mass of platelets grow to form the primary hemostatic plug in vivo. The plug must then be stabilized the fibrin strands during plasma protein coagulation for a long lasting effect rather then a temporary one.
Platelets also function in the healing process of cuts and scrapes. After the clot has formed the platelets then secrete chemicals that promote firbroblasts from the surrounding connective tissue into the wounded area healing the cut or forming a scar. Afterwards the clot is slowly dissolved by the fibrinolytic enzyme plasmin and the platelets are cleared by phagocytosis.
Disorders invovling platelets can include producing too many or too few platelets. Too many platelets can lead to the formation of blood clots in the blood stream leading to potential heart attacks or strokes. Too few and you can have an increased risk of bleeding or decreased effectiveness in clotting. But this is usually only a risk in platelet counts less then 80-100 million per ml. Spontaneous bleeding can occur if the platelet count drops below 10 million platelets per ml, this is usually seen in the form of tiny pin-prick haemorrhages on the skin (purpura).
There are many more factors involved in the clotting process, testing that is done specifically for platelet and clotting funtion, and diseases associated with platelets. For such a small, non-cell body, their role in the body is just as important as the heart or brain.