Facts About Platelets

Platelets are naturally produced by the human body to help prevent blood loss. They work with the protein fibrinogen, vitamin K and the mineral calcium to form clots. Clotting starts once the blood comes in contact with air. Scabs are external blood clots, while bruises are formed internally. A clot that forms inside a healthy vessel can reduce oxygen flow through the blood and lead to a stroke.

Characteristics

• Platelets, which make up about 20 percent of red blood cells, are produced inside bone marrow when megakaryocytes--large cells in the bone marrow--fragment. A normal count is between 150,000 to 350,000 platelets per microliter of blood.

Structure

• Normal platelets are shaped like plates, which is where their name comes from. Technically not cells--but rather portions of cells that circulate--platelets are designed specifically to stop bleeding. Proteins from platelets stick onto the walls of broken blood vessels as well as to each other as part of the clotting process. Granules inside platelets secrete proteins that help seal broken blood vessels.

Function

• Platelets move along the walls of blood vessels, which are lined with endothelium--a surface that does not allow anything to stick to it. Once there is an injury, breaking the endothelium, platelets begin sticking to the damaged area and to each other. Platelets are the first response to injuries, and possess the ability to change shape in order to cover the injured area.

Effects of Aspirin

• Due to its blood-thinning properties, aspirin can cause platelets to function improperly--by not allowing them to stick together. As a result, aspirin is often given to patients having heart attacks, because it prevents platelets from forming, allowing blood to flow more freely to the heart. Taking aspirin, however, can be dangerous to people with hemophilia and other disorders that put them at high risk for bleeding.

Too Many Platelets

• In rare instances, people produce too many platelets--sometimes a million or more per microliter. This increases the risk of blood clots, although many individuals with the disorder never have clotting problems.

Too Few Platelets

• Thrombocytopenia is the term for a condition in people who have too few platelets. While some people naturally produce fewer platelets than normal, in other instances platelets are destroyed or damaged. This can occur when bone marrow is damaged. Another cause is the production of abnormal endothelium, which allows platelets to stick together along the lining of unbroken blood vessels. Some drugs and medications also destroy platelets.