Haemostasis Flashcards
What is haemostasis, what 3 process does it include?
The process of stopping blood flow.
Keeping blood inside a damaged vessel whilst still allowing the blood to flow.
uses, vasoconstriction, platelet aggregation and coagulation.
How does vasoconstriction assist haemostasis?
Blood flow is under pressure so a strong clot cannot form.
Vasoconstriction cases a local reduction in blood flow in the effected area to allow a clot to form in arteries.
In veins and capillaries they do not have enough muscle so will just collapse.
How are thrombocytes stimulated to form?
Thrombocyte = platelet
Stimulated by the release of TPO from the liver (sometimes the kidney).
They assist growth and maturation of megakaryoblasts into megakaryocytes.
How are thrombocytes made through the myeloid line?
Common precursor > Megakaryoblast > Megakaryocyte > Platelet
How do platelet plugs form?
Key stimulus = exposure to collagen.
vWF released and promote the activation of platelets so they become sticky and aggregate together, stick to the collagen via integrin and fibronectin.
Platelet activating factor (PAF) is released by platelets and WBCs, activates more platelets and thromboxane A2 which increases aggregation.
This is a positive feedback mechanism
How do platelet plugs stop?
Formed through a positive feedback mechanism so they could just keep getting bigger.
But normal endothelium releases activators to prevent platelets binding, so the plug only forms in a localised region.
What is coagulation?
The process of converting a plug into a clot
What is the difference between the intrinsic and extrinsic pathways in coagulation?
The intrinsic pathway activates molecules already in the plasma, these will start a pathway and feed into the common pathway.
The extrinsic pathway forms new molecules in the plasma, these then feed into the common pathway.
Describe the common pathway of coagulation?
Activated factor X converted prothrombin into the activated form thrombin. Thrombin the converts soluble fibrinogen into insoluble fibrin forming a clot.
What is anticoagulation and name 2 mechanisms through which it works?
Stops continuous clotting.
- Inhibition of platelet adhesion.
- inhibition of coagulation pathways and fibrin production.
What is fibrinolysis?
The breakdown of fibrin into fragments by plasmin.
The fragments are released as fibrin degradation products (FDP) which act as anticoagulants
How is plasmin formed?
Plasminogen found in clots is converted to plasmin by thrombin and tPA (tissue plasminogen activator)
How is fibrinogen degraded?
Fibrinolytic agents in the saliva.
Where can inappropriate clotting form?
Scar tissue
Foreign surfaces (prosthetic heart valves)
Slow blood flow
Altered blood factors
What is disseminated intravascular coagulation (DIC)
Microclots form after severe trauma. These form due to the release of Factor III, use up all the platelets, factors and fibrin. There is an increase in FDP in order to decrease fibrin after the micro clot forms, this means no other clots can form, patient will bleed out.
