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Physiology

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Cardiovascular System

Question
16 out of 16
 

During Exercise the cardiac output risesupto 5 times, but pulmonary vascular resistance only few mm hg. Why? (AIPG 2010)



A Sympathetic stimulation causing vasodilatation

B Opening of parallel channels

C Pulmonary vasoconstriction

D J receptors

Ans. B Opening of parallel channels

During exercise there is an increase in CO due to increased HR and SV.

I. Peripheral resistance and DBP also increase due to sympathetic vasoconstriction. Sympathetic cholinergic system does cause Vasodilatation but only in few organs like SkeletalmuscleQ, Uterus and Sweat glands.

II. In Lungs there is not much rise in pulmonary vascular resistance because of opening of precapillary sphincters. They cause opening of more blood vessels leading to increasing in pulmonary perfusion.

III. But the vessels are arranged in parallel to each other, their resistances are added as

IV. So, more is the number of resistances (vessels) in parallel lower is the Total resistance (RT).

V. During exercise this mechanism counters the effect of sympathetic vasoconstriction in lungs and there is only small rise in pulmonary vascular resistance.

Cardiovascular System Flashcard List

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