Three Key Events:
1.
Vascular Spasm: vasoconstriction upon blood vessel damage, narrows luminal diameter
2.
Platelet Plug Formation & Coagulation:
Platelet Plug Formation:* accumulation of platelets in damaged vessel walls.
Coagulation:* conversion of liquid blood into a gel (clot).
Vascular Spasm
- Initiated by exposed collagen – slows flow of blood to minimize blood loss.
Platelet Plug Formation
1.
Adhesion: wherein platelets tether to the exposed collagen
2.
Activation: initiated by adhesion, produces intracellular rearrangement of action that results in spiky processes on platelets (star-shape).
3.
Aggregation: positive feed back loops.
- Activated platelets release ADP and thromboxane A2.
–
ADP makes other platelets stickier.
–
Thromboxane A2 stimulates ADP release.
Coagulation
- Intrinsic: coagulation factors in the blood trigger cascade.
- Extrinsic: coagulation factors released by tissues enter blood stream and
trigger cascade.
Extrinsic pathway is shorter than intrinsic pathway; they converge at factor X activation
Shared pathway:
- Activation of Factor X (halfway through intrinsic/beginning of extrinsic)
– Active
Factor X +
Factor V +
calcium ?
Prothrombinase
–
Prothrombinase +
Prothrombin (Factor II) ?
Thrombin
–
Thrombin +
Fibrinogen (Factor I) ?
Fibrin (loose mesh)
–
Fibrin (loose mesh) ?
Fibrin (strong mesh)
- Fibrin meshwork forms over platelet plug ? traps red blood cells and aggregating platelets.