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Difficulty: EasyHemodynamic and Coagulation Processes

A 24-year-old healthy male sustains a minor laceration to his forearm while cooking. Bleeding from the wound ceases within a few minutes due to an intact physiological hemostatic response. Arrange the following cellular and molecular events of hemostasis in the correct chronological order, beginning immediately after the initial vascular injury.

  1. 1Transient reflex vasoconstriction mediated by local endothelin release
  2. 2Platelet adhesion to exposed subendothelial von Willebrand factor via Glycoprotein Ib
  3. 3Platelet degranulation with the release of ADP, calcium, and thromboxane A2
  4. 4Conformational change of Glycoprotein IIb/IIIa receptors allowing fibrinogen binding
  5. 5Thrombin-mediated conversion of fibrinogen to a cross-linked fibrin mesh

Answer

The correct sequence begins with immediate vasoconstriction, followed by vWF-mediated platelet adhesion, platelet degranulation, GpIIb/IIIa activation for platelet aggregation, and finally fibrin mesh formation via the coagulation cascade.
Hemostasis proceeds in a highly regulated sequence: vascular spasm occurs immediately to reduce blood flow, followed by primary hemostasis (platelet adhesion, activation, degranulation, and aggregation to form a weak plug), and finally secondary hemostasis (coagulation cascade activation leading to a stable cross-linked fibrin mesh).

Step-by-Step Solution

1
Identify the immediate vascular response to injury.
Transient reflex vasoconstriction.
Vascular spasm is the first line of defense to limit initial blood loss.
2
Identify the initiation step of primary hemostasis.
Platelet adhesion via vWF and GpIb.
Platelets must anchor to the site of injury before they can recruit other platelets.
3
Determine the consequence of initial platelet adhesion.
Platelet degranulation releasing ADP and Thromboxane A2.
Granule release is necessary to recruit, activate, and amplify the platelet response.
4
Identify the mechanism of platelet aggregation.
GpIIb/IIIa conformational change and fibrinogen cross-linking.
This forms the initial, unstable primary hemostatic plug.
5
Identify the final stabilization step (secondary hemostasis).
Thrombin converting fibrinogen to a fibrin mesh.
Secondary hemostasis produces the definitive, stable blood clot.

Key Concept

Normal sequence of primary and secondary hemostasis
Estimated Time:1m 0s
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Topics

Hemodynamic and Coagulation Processes

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