Haemostasis Q's Flashcards
Q1. A 67-year-old man has a myocardial infarction caused by formation of a blood clot at a site of damaged endothelium due to coronary artery stenosis.
Which tunica has most likely been damaged?
a. tunica adventitia
b. tunica externa
c. tunica intima
d. tunica media
e. tunica mucosa
Answer = C, tunica intima.
The tunica intima comprises the endothelium, subendothelium and internal elastic lamina; it is the barrier between the blood and the rest of the vessel wall. Damage to the tunica intima would enable blood to reach cells/proteins that trigger clot formation.
A clinical research study investigates the effect of aspirin on haemostasis. Aspirin is found to inhibit thromboxane A2 biosynthesis, with a concomitant effect on platelets.
What aspect of platelet biochemistry is most likely affected?
a. activation
b. collagen interaction
c. endothelium interaction
d. thrombopoiesis (platelet production)
e. von Willebrand factor interaction
Answer = A, activation.
Thromboxane A2 has a number of effects in haemostasis, including vessel constriction and platelet activation. By inhibiting thromboxane A2 production, aspirin inhibits platelet activation. For this reason, aspirin can be used as an anti-platelet drug as well as an analgaesic.
A 56-year-old woman presents with idiopathic bleeding. She has no history of note. Laboratory investigations reveal an autoantibody against coagulation factor XI.
What aspect of haemostasis is most likely compromised?
a. clot growth
b. extrinsic pathway
c. fibrin cross-linking to the clot
d. intrinsic pathway
e. soft clot formation
Answer = D, intrinsic pathway.
Coagulation factor XI is part of the intrinsic pathway, therefore an autoantibody against coagulation factor XI will compromise its activity, resulting in the intrinsic pathway being inefficient or not functioning at all. The intrinsic pathway is responsible for fibrin formation (the propagation phase of the cell-based model), therefore collapse of the pathway will result in failure to produce fibrin, with a concomitant predisposition to bleed.
An 8-year-old boy with haemophilia A presents in the haemostasis clinic with a joint bleed into the right knee. Following joint aspiration, the doctor administers coagulation factor replacement therapy.
Which coagulation factor is most likely administered?
a. V
b. VIII
c. IX
d. X
e. XII
Answer = B, coagulation factor VIII.
The boy has haemophilia A which is due to a deficiency of coagulation factor VIII. This is therefore the coagulation factor that needs to be administered
A 22-year-old woman presents with severe menstrual bleeding.
Investigations (NORMAL VALUES)
Activated partial thromboplastin
time (APTT) 25 (21-34 s)
Prothrombin time (PT) 12 (10-14 s)
Platelets 200 (150-400 x 109/L)
von Willebrand factor (VWF) 20 (50-150 U/dL)
Which aspect of haemostasis is most likely compromised?
a. amplification
b. fibrin formation
c. initiation
d. propagation
e. soft clot formation
Answer = E, soft clot formation.
The von Willebrand factor level is well below the normal range. von Willebrand factor is essential for formation of the soft clot in primary haemostasis. If the von Willebrand factor level is low, primary haemostasis will be compromised and formation of the soft clot will be inefficient.
