Mechanism of blood coagulation

• The blood clots or coagulates within 2-6 minutes if it gets collected in a tube.
• It changes into semisolid jelly. This phenomenon is called coagulation or clotting.
• When skin or any other body part is cut, the blood flows out.
• But it quickly clots and thus stops the blood oozing out.
• It is called blood clotting. The normal clotting time is about 2-6 minutes.
• Blood coagulation is a very complicated process and is under a sensitive control.
• The capacity of blood to clot is essential to life.
• Hemorrhage occurs in absence of this self-sealing function.
• For blood clotting, blood platelets are responsible which takes place in many stages. They are :

i)Release of thromboplastin

• At the site of injury, thrombocytes come outside.
• When get exposed to air, they become damaged which after releases thromboplastin.

ii)Formation of thrombin

• Thromboplastin together with many clotting factors and calcium ions Ca⁺⁺ acts on the plasma protein prothrombin and thus converts the prothrombin into active thrombin.
• It is a proteolytic enzyme.

Prothrombin + Ca⁺⁺  (thromboplastin)  →  Active thrombin (in plasma)

Image source: wikipedia 

iii)Formation of fibrin

• Thrombin acts on the soluble plasma protein fibrinogen and converts it into insoluble fibrin.
• Fibrinogen   ( thrombin )    ⟶     fibrin

iv)Formation of blood clot

• The forms a network of fibre in which RBCs and WBCs are trapped to form a red solid mass called blood clot. 

Fibrin polymer  ( fibrin ) ⟶   insoluble fibrin clot

References:

i) https://www.ast.org/articles/2006/2006-10-274.pdf

ii) https://www.news-medical.net/health/Blood-Clotting-Process.aspx

iii) https://www.slideshare.net/mhnsathish/mechanism-of-blood-coagulation

Mechanism of blood coagulation