Platelets (or thrombocytes) help the blood clot by forming something called a platelet plug. They also help to promote other blood clotting mechanisms. Each microliter of blood contains approximately 150,000 to 400,000 platelets.
Platelets form in the bone marrow from large cells called megakaryocytes. These large cells break up into fragments. The cellular fragments are platelets. Platelets don't have a nucleus and don't reproduce. Instead, megakaryocytes produce more platelets when needed. Platelets generally last about 10 days on average.
Platelets contain several chemicals that assist in the blood's ability to clot including:
- Actin and myosin, which help them contract
- Various chemicals that help the coagulation process begin
- Various chemicals that attract other platelets
- Various chemicals that stimulate blood vessel repair
- Various chemicals that stabilize a blood clot