Question

Which of the following are mechanisms of intrinsic control of glomerular filtration (renal autoregulation)?

a. myogenic mechanism and tubuloglomerular feedback

b. tubuloglomerular feedback and the renin-angiotensin mechanism

c. sympathetic nervous system control and the renin-angiotensin mechanism

d. myogenic mechanism and sympathetic nervous system control

Answer 1

The correct option is A (myogenic mechanisms and tubuloglomerular feedback).

1 - Myogenic mechanism -

• When mean arterial pressure/ MAP , increases,  it stretches the wall of the afferent arteriole, which causes reflexive vasoconstriction.
• When the MAP decreases, the afferent arteriole reflexively relaxes and dilates, again maintaining glomerular blood flow and GFR.
• The myogenic mechanism provides rapid control of GFR in response to any changes in MAP.

2 - Tubuloglomerular feedback -

• Macula densa cells detect the concentration of sodium chloride in the tubular fluid.
• An increase in MAP increases GFR, which increases the concentration of sodium chloride in the tubule fluid. The macula densa responds by causing strong vasoconstriction of the afferent arteriole and bringing the GFR back down.
• When the MAP goes down, the resulting decrease in GFR reduces the sodium chloride concentration in the tubule fluid. Macula densa then causes vasodilation of afferent arterioles.