Rapid blood clotting is vital when a vessel is damaged to seal the break, limit blood loss and prevent entry of pathogens. When platelets, a type of blood cell without a nucleus, comes into contact with the damaged vessel wall they change to spheres with long, thin projections.

A cascade of changes results in the formation of a blood clot:

Platelets stick to the damaged wall and to each other forming a platelet plug.
Thromboplastin released triggers the cascade. Thromboplastin activates an enzyme that catalyzes the conversion of prothrombin to thrombin. Vitamin K and calcium ions must be present in the blood for this to take place.
Thrombin catalyzes the conversion of soluble plasma protein, fibrinogen, into the insoluble protein fibrin.
A mesh of fibrin forms that traps more platelets and red blood cells to form a clot.

	Created by Cecily Russell almost 7 years ago

A level Biology (SNAB: Processes) Note on Processes within the body, created by Cecily Russell on 08/01/2018.