Regulation of Coronary Circulation

Multiple Choice Questions (MCQs)

1. What effect does an increased heart rate have on coronary blood flow?
   a) Increases coronary blood flow
   b) Reduces the duration of diastole, decreasing coronary blood flow
   c) Reduces systolic blood pressure, increasing coronary blood flow
   d) Has no significant effect
   Answer: b) Reduces the duration of diastole, decreasing coronary blood flow
2. How does increased aortic pressure affect coronary circulation?
   a) Decreases coronary flow due to higher resistance
   b) Increases coronary flow due to a higher pressure gradient
   c) Reduces oxygen delivery to the myocardium
   d) Has no significant effect on coronary circulation
   Answer: b) Increases coronary flow due to a higher pressure gradient
3. Which receptor is associated with coronary vasodilation during sympathetic stimulation?
   a) α-Adrenergic receptors
   b) β-Adrenergic receptors
   c) Cholinergic receptors
   d) Endothelium-Derived Relaxing Factor (EDRF)
   Answer: b) β-Adrenergic receptors
4. What neurotransmitter is responsible for sympathetic vasodilation in coronary arteries?
   a) Acetylcholine
   b) Neuropeptide Y
   c) Norepinephrine
   d) Dopamine
   Answer: c) Norepinephrine
5. What is the role of Neuropeptide Y in coronary circulation?
   a) Causes vasodilation
   b) Maintains coronary resting tone
   c) Acts as a potent vasoconstrictor
   d) Increases oxygen uptake by the myocardium
   Answer: c) Acts as a potent vasoconstrictor
6. Which neurotransmitter acts on cholinergic receptors in the coronary endothelium?
   a) Norepinephrine
   b) Acetylcholine
   c) Neuropeptide Y
   d) Epinephrine
   Answer: b) Acetylcholine
7. What is the overall effect of parasympathetic stimulation on coronary circulation?
   a) Significant vasodilation
   b) Significant vasoconstriction
   c) Minor vasodilation due to EDRF release
   d) No effect on coronary circulation
   Answer: c) Minor vasodilation due to EDRF release
8. What happens to coronary blood flow when peripheral resistance increases?
   a) Coronary blood flow decreases
   b) Coronary blood flow increases
   c) Coronary flow remains unchanged
   d) Coronary vessels constrict fully
   Answer: b) Coronary blood flow increases
9. Which adrenergic receptor maintains the resting coronary vasoconstrictor tone?
   a) β-Adrenergic receptors
   b) α-Adrenergic receptors
   c) Cholinergic receptors
   d) Dopaminergic receptors
   Answer: b) α-Adrenergic receptors
10. Which factor primarily determines the duration of coronary blood flow?
    a) Systolic pressure
    b) Heart rate
    c) Peripheral resistance
    d) Aortic valve area
    Answer: b) Heart rate

Fill in the Blanks

1. Higher heart rates reduce the duration of ________, leading to decreased coronary blood flow.
   Answer: diastole
2. ________ pressure facilitates coronary blood flow by increasing the pressure gradient between the aorta and coronary arteries.
   Answer: Aortic
3. ________ adrenergic receptors are responsible for coronary vasodilation.
   Answer: β
4. The neurotransmitter ________ acts on adrenergic receptors during sympathetic stimulation.
   Answer: norepinephrine
5. The release of ________ by the endothelium during parasympathetic stimulation causes vasodilation.
   Answer: Endothelium-Derived Relaxing Factor (EDRF)

True or False

1. Coronary vasodilation during sympathetic stimulation is mediated by α-adrenergic receptors.
   Answer: False
2. Increased peripheral resistance decreases coronary blood flow.
   Answer: False
3. Acetylcholine is the neurotransmitter involved in parasympathetic stimulation of coronary vessels.
   Answer: True
4. Neuropeptide Y acts as a potent coronary vasoconstrictor.
   Answer: True
5. A faster heart rate increases coronary blood flow.
   Answer: False

Subjective Questions

1. Discuss how the autonomic nervous system influences coronary circulation.
   Answer:
   • Sympathetic Nervous System:
     • Involves β-adrenergic receptors (vasodilation) and α-adrenergic receptors (vasoconstriction).
     • Norepinephrine acts on β1 and β2 receptors, causing coronary vasodilation. Neuropeptide Y contributes to vasoconstriction.
   • Parasympathetic Nervous System:
     • Acetylcholine acts on cholinergic receptors, stimulating the release of EDRF, which causes minor vasodilation.
       Sympathetic effects are more prominent than parasympathetic effects, ensuring adequate blood flow during stress or exercise.
2. Explain the relationship between heart rate and coronary blood flow.
   Answer:
   Coronary blood flow occurs predominantly during diastole. Higher heart rates reduce the duration of diastole, limiting the time available for coronary perfusion. This reduction can compromise myocardial oxygen supply, particularly during strenuous activity or stress. Thus, heart rate is a critical determinant of the duration and efficiency of coronary circulation.