Hemostasis
Hemostasis is the cessation of blood loss from damaged vessel, prevent blood loss.
Arrest of bleeding is very important for maintenance of homeostasis.
Mechanism of Hemostasis
Hemostatic mechanism consists of 3 phase -
1. Vasocontrictive phase
2. Platelet plug formation
3. Blood clotting
1. Vasoconstructive Phase
Immediate but temporary closure of blood vessel resulting from contraction of smooth muscle with in wall of blood vessel.
When tissue or blood vessel is damaged and blood escapes from blood vessel.
Injury to blood vessel occurs.
Platelets migrates to blood vessels and connective tissue present in those blood vessels swell and adhere (stick) to collagen.
Which leads contriction to vessels.
Vasocontriction of vessel wall.
Narrow the opening of vessel.
2. Platelets plug formation
Clumping together of platelets, the key stages of this process are-
1. Platelet adhesion
2. Platelet release reaction
3. Platelet aggregation
Platelet plug formation is an accumulation of platelets that can seal up small breaks in blood vessels.
Platelet Adhesion
Initially platelet contract and stick to part of damaged blood vessels, such as collagen fibres of connective tissue.
Activated platelets, due to adhesion, platelets become activated and release chemicals serotonin, adenosin diphosphate (ADP).
Serotonin enhance vascular spasm.
Platelets Aggregation
Platelets aggregation, ADP helps in depositing of platelets over injured area. This process called platelets aggregation. Due to platelets aggregation, platelets become sticky and stickiness cause them to adhere to originate activated platelets.
So the damaged blood vascular wall activates increasing number of platelets that themselve attract more and more additional platelets, thus forming a platelets plug.
Escape from blood vessels of platelets.
Swell and adhere to the collagen in adjacent connective tissues.
Platelets become activated
Release chemicals like ADP, Serotonin
This attachment stimulates vasoconstriction.
Platelets become sticky and as more of them move into injured area they stick together.
Platelets aggregation (platelets plug formation)
Clog a small opening in the vessel.
3. Blood Clotting
Purpose of blood clotting is to plug the ruptured vessels so as to stop bleeding and prevent loss of vital body fluid.
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