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Cardiovascular System

2 out of 12

Standing to sitting change is: (AIPG JUN 2009)

A Immediate Increase in Venous Return

B Increase in heart rate

C Increase epinephrine

D Increased cerebral blood flow

Ans. A Immediate Increase in Venous Return

I. In the standing position, as a result of the effect of gravity on the blood, the mean arterial blood pressure in the feet of a normal adult is 180–200 mm Hg and venous pressure is 85–90 mm Hg.

II. The arterial pressure at head level is 60–75 mm Hg, and the venous pressure is zero.

III. If the individual does not move, 300–500 mL of blood pools in the venous capacitance vessels of the lower extremities, fluid begins to accumulate in the interstitial spaces because of increased hydrostatic pressure in the capillaries, and stroke volume is decreased.

IV. Symptoms of cerebral ischemia develop when the cerebral blood flow decreases to less than about 60% of the flow in the recumbent position.

V. If no compensatory cardiovascular changes occurred, the reduction in cardiac output due to pooling on standing would lead to a reduction of cerebral flow of this magnitude, and consciousness would be lost.So, under normal conditions the cerebral blood flow remains unchanged.

VI. The major compensations on assuming the upright position are triggered by the drop in blood pressure in the carotid sinus and aortic arch.

VII. The heart rate increases, helping to maintain cardiac output. Relatively little venoconstriction occurs in the periphery, but there is a prompt increase in the circulating levels of renin and aldosterone.

VIII. The arterioles constrict, helping to maintain blood pressure. So, when the person sits from a standing posture the venous return increases due to movement of 300-500 ml of blood pooled in the lower extremities towards the heart.

Effect on the cardiovascular system of rising from the supine to the upright position

Cardiovascular System Flashcard List

12 flashcards