Hemostasis is the arrest of bleeding, whether it be by normal vasoconstriction (the vessel walls closing temporarily), by an abnormal obstruction (such as a plaque) or by coagulation or surgical means (such as ligation)

1. HEMOSTASIS

17. Structure of platelet
membrane glycoproteins

20. Composition and function of platelet
alpha granule contents

22. PLATELET ROLE IN HEMOSTASIS
 Perform surveillance of blood vessel continuity
 Platelet-platelet interactions[primary hemostatic plug]
 Platelet – coagulation protein interactions[secondary
hemostatic plug]
 Aid in healing injured tissue

24. Platelet adhesion
 It is the attachment of platelets to collagen and other
components of endothelium.
 Platelets contain 2 collagen receptors :GPIaIIa and
GPVI which mediate direct collagen binding at low
shear rate.
 Platelets adhesion to collagen at high shear rate
however requires the presence of VWF and the
platelet VWF receptor,GPIIb/IX

27. Platelet activation
 Complex process
 Include changes in
 Metabolic biochemistry
 Platelet morphology
 Surface factors
 Membrane phospholipid orientation

28. Biochemical changes after activation
2
34
5
6 7
8

30. Platelet aggregation
 Newly arriving platelets flowing into the area become
activated by contact with agonists
 such as ADP and thromboxane A2[released
by the initial adherent and activated platelets]
 Products from the damaged tissue and
endothelial cells.
 Thrombin[a procoagulant enzyme generated
by tissue factor /F-VIIa]
 Mediated by fibrinogen which forms bridge between
platelets via Gp IIb Gp IIIa