Sun21November0452PM 14

Which one of the following statements best describes the process of renal autoregulation?

(Please select 1 option)

Requires autonomic innervation

Renal vascular resistance increases when the mean arterial blood pressure falls to between 80 and 100 mmHg

Reduces the effect of changes in arterial blood pressure on renal Na+ excretion This is the correct answer

Maintains normal renal blood flow when the mean arterial pressure falls to 50 mmHg

The principal alteration is to the diameter of the efferent arterioles Incorrect answer selected

Explanation

Autoregulation is the ability of a vascular bed to maintain perfusion despite fluctuations in systemic arterial pressure. The main organs that have the capacity to autoregulate are the kidneys, brain and heart.

The renal blood flow can be maintained between a mean arterial pressure (MAP) of 80 mmHg and 160 mmHg.

There are two main mechanisms of renal autoregulation, these are:

Myogenic response; is the function of vascular smooth muscle to contract in response of a stretching force. This is thought to be due to an influx of Ca2+ into the myocytes activated by stretch dependent voltage-gated ion channels.

Tubuloglomerular feedback (TGF); this mechanism leads to the constriction of the pre-glomerular afferent arterioles in response to an increase in luminal concentrations of Na+ in the macula densa of the distal convoluted tubule. An increase in arterial pressure will enhance tubular flow and improved glomerular filtration rate and reduced proximal tubular reabsorption.

Renal autoregulation minimises the impact of changes in arterial blood pressure on Na+ excretion.

Autoregulation is well preserved in denervated kidneys.

The effect of a fall in mean arterial pressure to the range 80-100 mmHg is likely to cause an increase in renal blood flow and a fall in renal vascular resistance.

Answer Statistics

1

8%

2

11%

3

22%

4

23%

5

38%

Times answered: 246