Question

Figure shows some of the effects of simulating mildly increased gravitational stress by lower body suction. For each of the physiological variables a–e below, select the most appropriate option from the following list of trends. 

1. Trend A. 

2. Trend B. 

3. Trend C. 

a. Forearm blood flow. 

b. Cardiac output. 

c. Mean arterial pressure. 

d. Total peripheral resistance. 

e. Renin secretion.

Answer 1

a. Option 3 Trend C. The forearm blood flow falls as part of the general vasoconstriction that helps to maintain arterial blood pressure. 

b. Option 3 Trend C. As the blood pools in the lower body due to suction, the filling pressure of the heart decreases and so the cardiac output falls. 

c. Option 1 Trend A. During this relatively mild gravitational stress, arterial pressure is quite well maintained by mechanisms that compensate for the shift of blood volume towards the feet. 

d. Option 2 Trend B. The shift of blood initiates reflex mechanisms to increase total peripheral resistance to help to maintain arterial pressure. 

e. Option 2 Trend B. The diminished blood flow to the kidneys with vasoconstriction related to the fall in cardiac output and output results in the release of renin from the juxtaglomerular apparatus that again helps to maintain arterial blood pressure.