Process of Hemostasis. (Click 👇Description for notes)

Описание: The Process of Hemostasis.

Hemostasis is the body's natural process to stop bleeding from an injured blood vessel. It occurs in three phases:

Vascular Spasm (Vasoconstriction): The damaged blood vessel constricts to reduce blood flow and limit blood loss. This is a reflexive response triggered by injury to the vessel wall.

Primary Hemostasis: Platelets form a temporary plug at the site of injury. This involves platelet adhesion, activation, and aggregation (explained below).

Secondary Hemostasis:A stable blood clot forms via the coagulation cascade, where clotting factors activate one another to convert fibrinogen into fibrin. Fibrin threads reinforce the platelet plug.

2. Platelet Activation:
Platelets are small blood cells that play a key role in clot formation. When a blood vessel is injured:
Platelets encounter exposed collagen and von Willebrand factor (vWF) in the damaged vessel wall.
They become activated, changing from a round to a spiky shape to increase surface area for interaction.
Activated platelets release substances like ADP, thromboxane A₂, and serotonin. These chemicals:
Attract more platelets to the site.
Stimulate vasoconstriction.
Enhance the activation of other platelets.

3. Platelet Adhesion
Platelets bind to the exposed collagen at the injury site.
This process is mediated by **von Willebrand factor (vWF)**, which acts as a bridge between the platelets and the collagen.
Platelets anchor themselves to the damaged vessel wall, initiating the formation of the platelet plug.

4. Platelet Aggregation
Once adhered and activated, platelets release signaling molecules (like ADP and thromboxane A₂) that recruit additional platelets to the site.
These recruited platelets adhere to one another via glycoprotein receptors on their surfaces (e.g., **GPIIb/IIIa receptors**) that bind fibrinogen.
This forms a clump of platelets, called the **platelet plug**, which temporarily seals the vessel.

5. Stabilization (Clot Formation)
The coagulation cascade activates thrombin, which converts fibrinogen to fibrin.
Fibrin strands weave through the platelet plug, stabilizing it and forming a firm blood clot.
The clot remains until the vessel is healed, after which it is dissolved by fibrinolysis.