Platelet Plug Formation: Key Concepts

Overview of Hemostasis

• Hemostasis is critical for survival as it stops bleeding.
• Divided into three steps:
  1. Vascular Spasm
  2. Platelet Plug Formation
  3. Blood Clot Formation
• Focus of this session: Platelet Plug Formation

Platelet Plug Formation

• Platelet plug helps stop blood flow by forming a "plug" of platelets.

Initial Steps

• Begins when a blood vessel is damaged.
• Von Willebrand Factor (vWF):
  • Secreted by endothelial cells.
  • Binds to exposed collagen in the vessel wall.
• Platelets have vWF receptors (gp1B receptors) which bind to vWF.

Platelet Activation

• Binding to vWF causes platelets to:
  • Change Shape: Increases surface area.
  • Express Fibrinogen Receptors (gp2b3a receptors): Anchors platelets.

Secretion of Granules

• Alpha Granules:
  • Release additional vWF to aid adherence and activation.
  • Release Platelet Derived Growth Factor (PDGF): Aids in long-term healing.
• Dense Granules:
  • Release Adenosine Diphosphate (ADP): Aids activation.
  • Produce and release Thromboxane (TXA2): Synthesized via enzymes like cyclooxygenase and thromboxane synthase.

Further Platelet Activation

• ADP and Thromboxane bind to receptors on additional platelets (P2Y12 and TP receptors).
• This binding activates more platelets.

Platelet Aggregation

• Fibrinogen:
  • Produced by the liver.
  • Binds to fibrinogen receptors on platelets.
  • Functions as a linking molecule between platelets.
• Platelets adhere to one another, forming a plug across the vessel opening.
  • Actin and Myosin:
    • Present in platelets, enable contraction.
    • Help form a compact, effective plug.

Key Proteins and Functions

• Actin and Myosin: Crucial for plug contraction and compacting.

Summary

• Platelet plug formation is essential in stopping blood flow by forming a stable plug.
• Involves activation, secretion, and aggregation processes.
• Critical proteins and molecules include vWF, fibrinogen, PDGF, ADP, and thromboxane.

Use these notes to review and understand the process of platelet plug formation as part of hemostasis.