Which substance is released by platelets during clotting?

RUHS, Jaipur, PB B.Sc Nursing Entrance-2024

Applied Physiology

Easy

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2024

Explanation

Platelets contain dense (δ) granules which are storage sites for various bioactive molecules.
Upon activation at a site of injury, platelets undergo a process called degranulation, releasing the contents of these granules.
Serotonin is a key substance released from these dense granules.
The primary role of the released serotonin is to act as a potent vasoconstrictor, narrowing the blood vessel to reduce blood flow and blood loss.

Option A: Fibrinogen is a plasma protein primarily synthesized in the liver. Although a small amount is stored in platelet alpha-granules, it is not the key substance released by platelets to initiate their functions; rather, it is the substrate that forms the fibrin clot.
Option B: Creatinine is a metabolic waste product from muscle metabolism and is excreted by the kidneys. It has no function in the blood clotting process.
Option D: Thromboplastin, also known as Tissue Factor, is released from damaged endothelial and subendothelial cells of the blood vessel wall, not from platelets. It is the primary initiator of the extrinsic coagulation pathway.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Substances released by platelets during hemostasis as background academic context rather than a clinical decision trigger.
Understanding the substances released by platelets is fundamental to comprehending how antiplatelet medications work. For example, drugs that block ADP receptors (e.g., clopidogrel) prevent platelet activation and aggregation.
This knowledge is crucial for assessing bleeding risk. Certain medications, like Selective Serotonin Reuptake Inhibitors (SSRIs), can deplete platelet serotonin stores, impairing vasoconstriction and potentially increasing bleeding time.
What if the patient has a platelet storage pool disorder? In this condition, the platelets have defective or absent dense granules. The patient would have a bleeding tendency because they cannot effectively release serotonin and ADP to promote vasoconstriction and platelet aggregation, even if their platelet count is normal.

How to Approach the Question

First, identify the core of the question: it asks for a substance specifically 'released by platelets'.
Next, evaluate each option based on its primary source and function in the body.
Consider Fibrinogen: Recall that it's a major plasma protein involved in the final clot structure, mainly from the liver.
Consider Creatinine: Recognize this as a common lab value related to kidney function and muscle metabolism, not clotting.
Consider Thromboplastin (Tissue Factor): Remember this initiates the extrinsic pathway and comes from damaged tissue, not platelets.
Consider Serotonin: Recall that it is a neurotransmitter but also stored in high concentrations in platelet dense granules for release during hemostasis.

Concept Tested & Keywords

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