Platelets: 8 Critical Roles in Hemostasis, Clotting, Wound Healing, and Immune Defense

Platelets (thrombocytes) are anucleate cell fragments (150–450 × 10⁹/L) essential for vascular integrity.

1. Primary Hemostasis (Platelet Plug): Adhesion (vWF-GPIb), activation (ADP, thromboxane A2), aggregation (GPIIb/IIIa-fibrinogen).
2. Vasoconstriction: Release serotonin, thromboxane A2 → vascular smooth muscle contraction.
3. Coagulation Amplification: Provide phospholipid surface (PF3) for tenase/prothrombinase complexes → thrombin burst → fibrin mesh.
4. Clot Retraction: Actin-myosin contraction pulls wound edges together.
5. Wound Healing: Release PDGF, TGF-β, VEGF, FGF → fibroblast proliferation, angiogenesis, re-epithelialization.
6. Antimicrobial Defense: Release defensins, kinocidins; phagocytose bacteria; form NET-like structures.
7. Inflammatory Modulation: Recruit leukocytes (P-selectin, chemokines); interact with monocytes, neutrophils.
8. Immune Complex Clearance: Bind C1q-opsonized complexes for splenic removal.

Thrombocytopenia or platelet dysfunction causes mucocutaneous bleeding (petechiae, epistaxis, menorrhagia); thrombosis risks arise from hyperreactivity or elevated counts.