Platelets get activated when they come in contact with?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2016

Applied Physiology

Easy

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2016

Explanation

Platelet activation is a critical first step in forming a blood clot at the site of vascular injury.
When a blood vessel wall is damaged, the subendothelial matrix is exposed to the bloodstream.
Collagen is a key protein component of this subendothelial matrix.
Platelets have specific surface receptors that bind directly to exposed collagen fibers.
This binding event is the primary trigger that initiates the cascade of platelet activation, leading to shape change, degranulation, and aggregation.

Option A: Heparin is an anticoagulant medication. Its function is to prevent blood clot formation by enhancing the activity of antithrombin, which inhibits key clotting factors like thrombin and Factor Xa. It does not activate platelets.
Option C: Fibrinogen is a plasma protein that is essential for platelet aggregation, but it does not initiate activation. It acts as a bridge, linking platelets together, but only after they have already been activated by another stimulus like collagen or thrombin.
Option D: The intact endothelium (the inner lining of blood vessels) actively prevents platelet activation. It provides a smooth surface and releases inhibitory substances like prostacyclin (PGI2) and nitric oxide (NO).

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain The concept tested is the initial trigger for platelet activation in the process of primary hemostasis as background academic context rather than a clinical decision trigger.
Understanding the mechanism of platelet activation is fundamental for nurses administering antiplatelet medications like aspirin or clopidogrel, which are used to prevent heart attacks and strokes.
Knowledge of this process helps in assessing patients with bleeding disorders. For example, in von Willebrand disease, impaired platelet adhesion to collagen leads to increased bleeding.
What if? If a patient has a deficiency in the platelet receptor for collagen (e.g., a rare GPVI deficiency), they would experience a mild to moderate bleeding tendency because the initial step of platelet activation is impaired, even with normal platelet counts.

How to Approach the Question

First, identify the core physiological process in the question: 'platelet activation'.
Recall the sequence of events in hemostasis (the process of stopping bleeding).
Consider the normal state: platelets circulate without clotting. What prevents them? The healthy endothelium.
Consider the trigger for clotting: an injury. What does an injury to a blood vessel expose? The underlying structures.
Evaluate each option's role: Heparin is a drug that prevents clotting. Fibrinogen is involved in aggregation (a later step). The endothelium prevents activation. Collagen is the subendothelial protein that is exposed upon injury.
Conclude that contact with exposed collagen is the initial trigger for platelet activation.

Concept Tested & Keywords

Concept Tested: The concept tested is the initial trigger for platelet activation in the process of primary hemostasis.
Stem keywords: Platelets, activated, contact
Lead-in keywords: BEST, MOST RELEVANT CLUE
Negative lead-in flag: false

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