Hemostasis is the maintenance of blood flow is fluid state within the vascular system, the major components of hemostasis are vascular system, platelets, coagulation factors, inhibitors of coagulation and fibrinolytic system. details are given

1. Muhammad Asif Zeb
LecturerHematology
IPMS-KMU

2. DEFINITION
 The term haemostasis means prevention of blood
loss.
 Haemostasis is the arrest of blood flow and
control of hemorrhage from an injured blood
vessels.
or
 It is the process by which bleeding at any site is
arrested by formation of hemostatic plug.
 Or
 Maintenance of normal blood flow within the
circulatory system

3. Prime function of hemostasis
 To maintain blood in fluid state.
 To arrest bleeding followed by trauma
 To remove platelet plug when healing is
complete.

5. Type of hemostasis
 Primary hemostasis
Formation of PLT plug after vessel injury
 Secondary hemostasis
Due to coagulation protein

8. Events in Hemostasis
 Vascular Constriction
- local myogenic spasm
- local autacoid factors from traumatized tissues
and platelets
- nervous reflex

9. Structure of Platelet

10. STAGES OF
PRIMARY HEMOSTASIS
 Platelet Adhesion
 Platelet Activation and release
reaction
 Platelet Aggregation

11. platelet adhesion

14. Platelet activation :
platelet release action

15. Platelet aggregation

16. Clot formation

17. Secondary hemostasis
 “Cascade of reactions” by Macfarlane,
R.G.,1967
It states that ‘inactive’ enzymes are activated, and
the ‘activated’ enzymes in turn activates other
inactive enzymes until final step is reached.

18. Clotting or coagulation Factors
Factor I Fibrinogen
Factor II Prothrombin
Factor III Thromboplastin
Factor IV Calcium
Factor V Labile factor, or proaccelerin
Factor VI Non – existent
Factor VII Stable factor or proconvertin
Factor VIII Antihaemophilic factor / globulin A
Factor IX Christmas factor or Antihaemophilic factor B
Factor X Stuart – Prower factor
Factor XI Plasma thromboplastin antecedent or
Antihaemophilic factor C
Factor XII Hageman factor or Contact factor
Factor XIII Fibrin stabilizing factor or Laki – Lorand factor

19. Secondary hemostasis

20. Blood coagulation
 The clotting mechanism involves a cascade of
reactions in which clotting factors are activated.
 Most of them are plasma proteins synthesized by
the liver (vitamin K is needed for the synthesis of
factor II,VII, IX and X).
 They are always present in the plasma in an
inactive form.
 When activated they act as proteolytic enzymes
which activate other inactive enzymes.
 Several of these steps require Ca++ and platelet
phospholipid.

21. Mechanism
Clotting pathway is activated by:
 Intrinsic pathway
 Extrinsic pathway
 Common pathway

22. Intrinsic pathway
 The initial reaction is the conversion of
inactive factor XII to active factor XIIa.
 Factor XII is activated in vitro by exposing
blood to foreign surface (glass test tube).
 Activation in vivo occurs when blood is
exposed to collagen fibers underlying the
endothelium in the blood vessels.

23. Extrinsic pathway
 Requires contact with tissue factors
external to blood.
 This occurs when there is trauma to the
vascular wall and surrounding tissues.
 The extrinsic system is triggered by the
release of tissue factor (thromboplastin
from damaged tissue), that activates factor
VII.
 The tissue thromboplastin and factorVII
activate factor X.

24. Common pathway
 It involves the activation of factor X to Xa
via intrinsic and extrinsic pathway.
 Xa further activates prothrombin to active
enzyme thrombin.
 Thrombin act on fibrinogen to fibrin.
 Factor XIII helps in the formation of
stabilized fibrin.

26. Clot formation

28. Fibrinolytic system

29. Fibrinolysis
 The process of removing unwanted
insoluble deposit formed as a result of
coagulation is called fibrinolysis.
 It is a physiological process in which fibrin
clot is broken down by enzyme into
soluble fragment.

31.  Activators of plasminogen:
◦ TPA
◦ Thrombin
◦ XIIa
◦ Kallikerin
◦ HMWK
Inhibitors of plasmin :
Alpha 1 anti trypsin
Alpha 2 anti plasmin
Alpha 2 macroglobulin