Question

When a patient’s mean arterial blood pressure falls by 50 per cent 

A. Renal blood flow falls by less than 10 per cent. 

B. Glomerular filtration falls by about 50 per cent. 

C. There is an increase in the circulating aldosterone level. 

D. Renal vasoconstriction occurs. 

E. Urinary output ceases.

Answer 1

A. False Autoregulation cannot compensate for such large falls. 

B. False It falls to about zero when glomerular capillary pressure falls below the sum of intracapsular pressure plus plasma oncotic pressure – around 30–40 mmHg.

C. True Due to release of renin and angiotensin formation, aldosterone is secreted. 

D. True Reflex sympathetic vasoconstriction due to greatly decreased baroreceptor stimulation. 

E. True When glomerular filtration stops, urinary output stops.