Heart Failure & Valvular Diseases Q 11 - Gyan Darpan : Learning Portal
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Thursday, 28 April 2022

Heart Failure & Valvular Diseases Q 11

Stimulation of the sympathetic nervous system produces which of the following responses?
     A. Bradycardia
     B. Tachycardia
     C. Hypotension
     D. Decreased myocardial contractility

Correct Answer: B. Tachycardia

Stimulation of the sympathetic nervous system causes tachycardia and increased contractility. The other symptoms listed are related to the parasympathetic nervous system, which is responsible for slowing the heart rate. Studies have mainly focused on the role of the sympathetic nervous system, specifically evaluating the effect of increased sympathetic activity. It has been well documented that heart rate variability is diminished, and heart rate increases, before ventricular tachycardia in humans, which is likely reflective of increased sympathetic tone.

Option A: Via the vagus nerve, the parasympathetic nervous system stimulates neurons that release the neurotransmitter acetylcholine (ACh) at synapses with cardiac muscle cells. Acetylcholine then binds to M2 muscarinic receptors, causing the decrease in heart rate that is referred to as reflex bradycardia.
Option C: A key modulator of blood viscosity is the renin-angiotensin system (RAS) or the renin-angiotensin-aldosterone system (RAAS), a hormone system that regulates blood pressure and water balance. When blood volume is low, juxtaglomerular cells in the kidneys secrete renin directly into circulation.
Option D: The activation of M2 receptors reduces the contractility of atrial cardiomyocytes, thus reducing, in part, the overall cardiac output of the heart as a result of reduced atrial kick, smaller stroke volume, and slower heart rate. Cardiac output is determined by heart rate and stroke volume (CO = HR x SV).

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