Question

How do platelets assist in blood clotting?

Answer 1

Platelets normally circulate in the blood and are involved in the formation of plug over damaged blood vessels.

Explanation:

The immediate process of stopping blood after injury is known as " hemostasis " and involves 3 steps

1) blood vessel spasms
2) formation of platelet plug
3) blood coagulation ( clot formation)

Platelets in the circulating blood bind to specific membrane receptors outside the injured endothelium ( of blood vessel).

This activates platelets integrin which results in the tight binding of the platelets to the extra cellular matrix.

The activated platelets release their contents into the blood plasma activating more platelets in the blood.

Fibrinogen and glycoproteins cause adjacent platelets to clump together. This is called platelet aggregation.

Later , thrombin is produced and it converts fibrinogen to fibrin , forming a mesh with platelets. Thus plugging the break in the blood vessel wall.
Within minutes, the fibrin mesh work begins to contract, squeezing out its fluid contents. This is called clot retraction and is the last step in coagulation.
It yields a resilient insoluble clot that can withstand the friction of blood flow.