SBA — Single Best Answer · Review
Question 301
Physiology → Haematology
Classification
Question
SSBAOptions
Explanation
The intrinsic pathway begins with collagen and factor XII. APTT assesses the intrinsic and common pathways, whereas PT assesses the extrinsic and common pathways.
Option Validity
A) Factor VII is associated with the extrinsic pathway, which is assessed by PT. It is not the collagen-triggered intrinsic pathway described in the stem.
B) Factor X participates in coagulation but is not identified as the collagen-initiated factor. Bleeding time assesses platelet and vascular haemostasis rather than the intrinsic coagulation pathway.
D) Factor XIII participates in stabilisation of the fibrin mesh after fibrin has formed. PT assesses the extrinsic and common pathways and does not match this combination.
E) Factor VIII deficiency affects the intrinsic pathway in haemophilia A, but factor XII is associated with initiation by collagen. Bleeding time assesses primary haemostasis rather than intrinsic coagulation.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Blood Coagulation and Activated Partial Thromboplastin Time, pp.70-72.