Which of the following is an anticoagulant found in blood?

Raj. CHO - 2023

Applied Physiology

Easy

Appeared in: Raj. CHO - 2023

Explanation

Heparin is a natural anticoagulant produced by the body's mast cells and basophils.
It functions by binding to and activating antithrombin III, a protein in the blood.
The heparin-antithrombin III complex is a potent inhibitor of thrombin (Factor IIa) and Factor Xa, which are critical enzymes required for blood clot formation.
By inhibiting these factors, heparin effectively prevents the conversion of fibrinogen to fibrin, thus stopping the formation of a clot.

Option B: Fibrinogen (Factor I) is a procoagulant. It is a soluble plasma protein that is converted by thrombin into insoluble fibrin threads to form the structure of a blood clot.
Option C: Collagen is a structural protein in the subendothelial layer of blood vessels. Its exposure following an injury initiates the intrinsic pathway of coagulation by causing platelets to adhere and become activated. Therefore, it promotes, not prevents, clotting.
Option D: Fibrin is the end product of the coagulation cascade. It is an insoluble protein that forms a mesh, trapping platelets and red blood cells to form a stable clot. It is the substance of the clot itself, not an anticoagulant.

Visual 1: Diagram - The coagulation cascade, showing the conversion of prothrombin to thrombin and fibrinogen to fibrin. The diagram should clearly mark the inhibitory action of the Heparin-Antithrombin III complex on Factor Xa and Thrombin.

Clinical Relevance

Nursing practice connection: Knowing Physiology of hemostasis and natural anticoagulants helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses are responsible for the safe administration of heparin, which requires careful calculation of doses and monitoring for signs of bleeding (e.g., hematuria, epistaxis, bruising).
Understanding the therapeutic range for aPTT (activated Partial Thromboplastin Time) is crucial when managing patients on unfractionated heparin infusions to prevent under- or over-anticoagulation.
Nurses must know that protamine sulfate is the specific antidote for heparin and ensure it is accessible for emergency use in case of life-threatening hemorrhage.

How to Approach the Question

First, identify the keyword in the question stem: 'anticoagulant'. This term means a substance that prevents or inhibits blood clotting.
Analyze each option's role in hemostasis (the process of stopping bleeding).
Recall that 'fibrin' and 'fibrinogen' are central to the formation of a clot. Fibrinogen is the precursor, and fibrin is the final structure. This makes them procoagulants.
Remember that exposed 'collagen' from a damaged blood vessel wall is a primary trigger for the clotting process, making it a procoagulant initiator.
By elimination, or through direct knowledge, identify 'Heparin' as the substance that works against the clotting process.

Concept Tested & Keywords

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