Hemostasis and blood coagulation

Haemostasis: is the physiological arrest of hemorrhage at sites of vascular leakage.



There are mainly 5 systems which interact together to ensure hemostasis, namely:
1. Platelets.
2. Coagulation Factors.
3. Natural Coagulation inhibitors.
4. Fibrinolytic system.
5. Vascular factors.
Platelets structure

External coat: glycoproteins and glycolipids are important in platelets adhesion and aggregation.
Plasma membrane:
Lipids mainly phospholipid (PF3)
Glycoproteins mainly GP 2b3a …… site for FNG binding
GP 1a ……… site for collagen binding
GP 1b ……… site for VWF binding
Cytoplasmic granules:
alpha granules contain FNG, VWF, Fibronictin, F5, F8, ?-thromboglobuline, heparin antagonist- PF4, PDGF, others)
Dense granules contain (ADP, ATP, 5-HT, Ca++, PO4)
Mitochonderia, lysosomes.
Open canalicular system, to increase reactive platelets surface.
Platelet cytoskeleton: including microtubules and actine.
Dense tubular system: platelets Ca store.
Platelets functions

Primary plug formation (adhesion, shape changes, aggregation, release)
Procoagulant activity
Clot retraction
Vascular constriction, vascular repair, leukocyte recruitment, and inflammatory response.
Fibrinogen Factor I
Prothrombin Factor II
Tissue factor Factor III; tissue thromboplastin
Calcium Factor IV
Factor V Proaccelerin; labile factor
Factor VII Proconvertin
Factor VIII Antihemophilic factor (AHF)
Factor IX Christmas factor
Factor X Stuart-Prower factor
Factor XI Plasma thromboplastin antecedent
Factor XII Hageman factor
Factor XIII Fibrin-stabilizing factor
Prekallikrein Fletcher factor
Fitzgerald factor HMWK kininogen

Half life of all factors range from 10-65 hrs except F7 5-7 hrs

Coagulation pathways old version depend on extrinsic, intrinsic and common pathways.

Coagulation pathways new version consist of:
Initiation: TF binding to F7 and form F7a.
Amplification: F7a activate both F9 and F10. F10a lead to generate small amount of thrombin which amplify the process by activate the F5 and F8.
Feedback inhibition: TFPI, Antithrombin, Activated protein C.
Fibrinolysis system.