Hemostasis

What are the components of hemostasis

Platelets “Thrombocytes”

The Coagulation system - Clotting cascade

Endothelium
- Inside lining of a vessel
- Collagen inside the vessel wall

Platelets

Production controlled by thrombopoietin and has a life span of 5-10 days

Removed from circulation by tissue macrophage system mainly in spleen

Endothelium

Promotes blood flow and prevents platelet aggregation
- Prostacyclin, Nitric oxide, ADP

VWF helps platelets stick to collagen promoting aggregation to the injury site

Merging of the two pathways

Occurs at activation of Factor X = Xa

Clotting cascade continues and prothrombin is converted to thrombin, which acts on fibrinogen to produce fibrin

Can be triggered directly by snake venom, amniotic fluid embolism, acute pancreatitis

What is the Fibrinolytic System

Coagulation must be contained to site of injury so there are coag inhibitors

Adequate blood flow: Clearance of coag factors by the liver

Antithrombin 3 inactivates thrombin, and decreases the conversion of fibrinogen to fibrin

Protein C and S - Vit. K dependent proteins

Dissolution of Clots

Plasminogen principal activator of fibrinolytic system is t-PA. Plasminogen-inactive in blood '

Converts plasminogen to plasmin and digests the fibrin strand

t-PA is produced by endothelial, liver and kidney cells, naturally and normally

Cleaves fibrin knots and digests some clotting factors

What is the fibrin breakdown

D-dimer and antithrombin → release fibrin degradation products

What are the essential components of hemostasis

Adequate clotting factors
Vit. K
Healthy Liver (Digests fat for absorption of VIt. K )
calcium
Adequate platelets
Intact fibrinolytic system

Platelets (Part of the CBC)

High risk for bleeding when platelets <50,000
Thrombocytosis: >400,000 indicated increase in platelet production or decrease in destruction

Abnormal platelet activity can cause either bleeding or thrombosis

Prothrombin time (PT)/INR

Normal: 11-12.5 sec
Protein produced by liver, needs vit. K

Measures potential defect in clotting ability of 5 plasma coagulation factors
Used in extrinsic and common pathway

INR: Normal 2-3 sec for DVT, Heart valve replacement 2.5-3.5

Partial Thromboplastin Time PTT

Normal: 30-40 sec

Can check aPTT normal 21-35 sec.

Intrinsic pathway

Used to monitor heparin