📚 > Physiology > Hematology > Hemostasis_>

Platelet Plug Formation

Injury

↓

Damage to endothelial cells and exposure of collagen

↓

Von Willebrand Factor (vWF) is released by damaged endothelial cells

↓

vWF binds to exposed collagen.

Platelet Adhesion

• Through following receptors, the platelet attaches to the exposed collagen:

  • Gp Ib ↔ vWF ↔ Collagen

  • Gp Ia/IIa ↔ Collagen

  • Gp VI ↔ Collagen

Platelet Activation & Release Reaction

• Activation of the receptors → intracellular signaling events → release of alpha and dense granule.

• Alpha (α) granules:

  • Growth factors → Wound healing

  • Von Willebrand factor → Platelet aggregation

  • Fibrinogen → Platelet aggregation and coagulation

  • Factor V → Coagulation

• Dense granules:

  • ADP → Platelet aggregation

  • Serotonin → Vasoconstriction

  • Calcium → Coagulation

• Enxyme COX-1 and thromboxane synthase synthesize TxA2 from membrane phospholipids → TxA2 is released into the blood.

• Parallel coagulation cascade on platelet surface → formation of thrombin → released into the blood.

• Platelet changes shape (extend finger-like projection) → Increase surface area.

• Conformational changes in Gp IIb/IIIa → binds with fibrinogen.

Platelet Aggregation

• More platelets are activated by:

  • ADP ↔ P2Y12

  • TxA2 ↔ TP

  • Thrombin ↔ PAR-1 (Protease-activated receptor-1)

• Activated platelets undergo similar changes as described above including:

  • Conformational changes in Gp IIb/IIIa → bind with fibrinogen which acts as bridge between two platelets. vWF can also serve as bridge between platelets.

  • More release reaction→ More platelet activation → So on… → in this way, platelets are recruited till the wound is plugged → this plug is called primary hemostatic plug or primary platelet plug → fibrin synthesized by coagulation strengthens it → called secondary plug.

---

Next >>

▶️ Blood Coagulation Cascade