Platelets, Coagulation and Haemostasis

Blood Platelets

A human body is a structure consisting of various organ systems and mechanisms to regulate the different function. During a cut or an injury our body starts bleeding, but after some time the blood clots and bleeding ceases. What is the mechanism of this clotting? How do platelets and coagulation help in homeostasis?

Platelets and Coagulation

Blood is a body fluid which circulates throughout the body under high pressure and helps the body to maintain a homeostasis. The constant blood loss can result in death. Hence, we need a mechanism to counteract the blood loss. The mechanism which helps the body to prevent the blood loss is called hemostasis. For hemostasis, the body needs both platelets and coagulation system. Platelets are the specialized blood cells, which helps in the healing process. Under normal condition,  the blood is fluid in nature but hemostasis leads to solidification of blood called blood clots.


It is a physiological defensive reaction to an injury or a cut; it seals the blood vessels and thus helps in healing. Mainly platelets, endothelial cells of blood vessels, and blood proteins are responsible for hemostasis. Hemostatic mechanism proceeds in the following series of steps:

  • Changes in blood vessel cells
  • Blood clot formation
  • Platelet plug formation

It takes place in two stages:

Primary hemostasis – it is caused when bleeding ceases or reduced by contraction of the blood vessels and thrombin signals for platelets assembly and form a loose platelet plug.

Secondary hemostasis – it includes the action of blood proteins and coagulation factors in a sequence to reinforce the platelet plug and marks the onset of the healing process. Blood coagulation is provoked by extrinsic pathway i.e.; tissue damage but intrinsic pathway (internal messengers) intensifies the coagulation.

Coagulation of blood is a lengthy process occurring within a few minutes where numerous coagulation factors come into play.

To know more about the processes in detail, visit BYJU’S.

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