The platelets are small particles found in the blood. They play a role in blood coagulation, which is the mechanism to stop bleeding.
They are the first responders
After a cut, the wound starts to bleed. Blood runs out because there is a breach in the blood vessels. The body launches an alarm, a “9-1-1 call”, because the breach must be sealed. This is done by the blood coagulation system. The platelets are the first cells to respond.
The platelets at work change their shape
When they arrive at the site of the breach, platelets alter their shape. They generate tentacles and bind together. They form the first stage of the clot (called white clot because it’s only made of platelets). They release special substances which attract and recruit other platelets.
A tight network is formed
The substances released by platelets activate the process of blood coagulation.
Blood coagulation is a succession of complex chemical reactions involving special proteins circulating in the blood. This process leads to the formation of small filaments called fibrin.
One could compare this process to the formation of gelatin. As those small filaments accumulate around the platelets, some red blood cells get passively trapped and this lead to the formation of a sealed net, now called a red clot.
The breach is sealed
The clot closes the breach in the vessel, thus keeping the blood inside. The repair process can now begin.