Question

Describe the three responses to hemostasis. Explain the two subcategories for the third response, and when this response is needed.

Answer 1

Hemostasis is a natural process , which stops blood loss when injury occurs.

It involve three steps:

1. Vascular spasm (Vasoconstriction)
2. platelet plug formation
3. Coagulation.

Vascular spasm

• It is the narrowing of blood vessel, which cause increase in blood pressure , but it can decrease blood flow and blood loss.
• Vasoconstriction is caused by thromboxane A2.
• Vasoconstriction only last for few minutes during hemostasis.During inflammation that follows the injury, it is replaced by vasodilation as healing process begins.

Platelet plug formation

• platelets adhere to damaged endothelium and helpin formation of platelet plug , which temporarily seal the break in the vessel wall.
• The activated platelets will release factors for the stimulation of further platelet activation, some factors stimulate coagulation cascadeand maintain vasoconstriction.
• During platelet aggregation , platelet bind to non willebrand factor and fibrinogen to stick together and seal the break in the endothelium

Coagulation

• Coagulation cascade is a series of reaction, which is classically divided into three pathway : the contact ( known as intrinsic pathway ), tissue factor ( extrinsic pathway) and common pathway.
• The intrinsic pathway occur when negatively charged molecule contact causes a cascade of factors that produce factor X.
• The Extrinsic pathway occur when tissue damage cause release of tissue factor , creating smaller cascade that produce factor X .
• The common pathway merges both intrinsic and extrinsic pathways.
• Secondary hemostasis involves factors of coagulation cascade , which collectively strengthen the platelet plug.
• Coagulation can be harmful if it obstruct other blood vessel.