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Hemostasis

Prevention of blood loss

Steps:

i.Vascular spasm

ii.Formation of platelet plug

iii.Formation of blood clot as a result of blood coagulation

iv.Eventual growth of fibrous tissue into blood clot

Prothrombin

•Plasma protein –synthesized from LIVER

•Vit. K required for synthesis

•Alpha2-globulin

•Mol. Wt –68,700

•15mg/dl

•Unstable protein –splits into smaller compunds

Thrombin –mol wt. 33,700

Fibrinogen

•100 –700 mg/dl

•Mol wt. –340,000

•Synthesis –Liver

Clot Retraction -Serum

•Within few minutes

•20 to 60 min –most fluid of clot expressed

•Serum –Fibrinogen & most of clotting factors removed

•Platelets –Platelet thrombosthenin

Actin

Myosin

•Thrombin

•Calcium –from mitochondria, endoplasmic reticulum, golgiapparatus of platelets

Vicious Circle of Clot Formation

•Clot extends within minutes to surrounding blood

•Proteolyticaction of thrombin on clotting factors

Activation of ProthrombinActivator

•Trauma to vascular wall & adjacent tissues

•Trauma to blood

•Contact of blood with damaged endothelial cells / collagen

Extrinsic Pathway

Intrinsic Pathway

EXTRINSIC PATHWAY

Traumatized vascular wall / traumatized extravasculartissue that comes in contact with blood

•Explosive

•Severe trauma –within 15 seconds

INTRINSIC PATHWAY

Trauma to blood itself

OR

Exposure of blood to collagen from traumatized blood vessel wall

•Slower to proceed

•1 –6 min

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