Blood clots occur at points inside blood vessels that have been damaged, and blood clot formation occurs largely because of the platelets in the blood. Platelets are pieces of blood cells that have a sticky surface that allows them to bond to each other and to the walls of the veins and arteries. When there is a higher than normal level of platelets in the blood, clots can occur in areas of vessels where there are no injuries.
Normally, when a blood vessel is damaged, there is a chemical signal that summons platelets to the area. The protective seal of proteins formed by the platelets is called fibrin, and remains over the area until the damage has been healed. Once healed, the blood clot formation is dissolved by the body and the obstruction is carried away. In a healthy body, this process occurs when there is any size of injury to the vessel, either from an external wound or inside a vessel.
Sometimes there is a higher than normal level of platelets in the blood, and this can cause large clots to form when there is no injury. When blood clots form inside veins that have not sustained injuries, there is a possibility of the body being incapable of dissolving the clot on its own. This can result in a stroke or heart attack if left undiagnosed and untreated. Anticoagulants can be administered to individuals with high levels of platelets in order to stop this dangerous blood clot formation.
Blood clot formation occurs for different reasons in arteries and in veins. In veins, the vessels that return blood to the heart, blood clot formation can occur when a person remains inactive for a long time, such as on a long airplane flight. This inactivity causes blood to stagnate and collect in the veins, and if inactivity continues, this buildup can completely obstruct a vein in a condition called deep vein thrombosis. Arteries are the vessels that carry blood from the heart to different parts of the body; in these vessels, plaque contained in the blood can build up and block arteries. These clots are called arterial thrombi.
Other conditions can increase the chances of blood clot formation in the veins. High cholesterol, high blood pressure, obesity, lack of exercise, or a family history that includes blood clots can all contribute to the likelihood of an individual developing clots. Those recovering from illness or injury or who are bedridden due to pregnancy or post-surgery recuperation can also be susceptible to developing blood clots.