The platelets in the blood largely contribute to blood clot formation. Platelets are the parts of blood of cells that have a sticky surface. The sticky surface allows them to bond with each other and to the walls of the veins and arteries which may require a blood clot.
Upon any damage to a blood vessel, a chemical signal stimulates platelets to rush to the affected area, to form a protective seal of proteins (fibrins). They stay in there until the damaged area has healed. After healing, the blood clot formation dissolves into the body and the obstruction that may have formed is carried away from the area. Every healthy body is capable of responding with a high number of platelets stimulated for blood clot formation whenever there is an internal or external injury.
Too many platelets in the blood can cause clots to form even when there is no injury. These clots obstruct the arteries and veins as they may find it difficult to dissolve the clots. If a person is inactive for long periods of time, the blood can become stagnate and collect within the veins. The build up of the blood prompts conditions such as deep vein thrombosis. In arteries, plaque can build up in the blood and block the arteries causing arterial thrombi. Such blood clots cause heart attacks or strokes if the condition is not diagnosed early enough and remains untreated. People with such conditions of high platelets receive anticoagulants to stop the dangerous type of blood clot formation.