Question at position 11 Which of the following BEST describes the autoregulatory renal response to an INCREASE in mean arterial pressure?Vasoconstriction of the afferent arteriole, leading to a decreased glomerular filtration rateVasodilation of the afferent arteriole, leading to a decreased glomerular filtration rateVasodilation of the efferent arteriole, leading to a decreased glomerular filtration rateVasoconstriction of the afferent arteriole, leading to an increased glomerular filtration rate

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BlackTom AI · Accepted Answer

When mean arterial pressure rises, the kidneys engage auto-regulatory mechanisms to keep glomerular filtration rate (GFR) relatively constant.
Option 1: Vasoconstriction of the afferent arteriole, leading to a decreased glomerular filtration rate. This is the classic myogenic autoregulatory response: increased pressure causes the afferent arteriole to constrict, reducing hydrostatic pressure in the glomerulus and thus lowering GFR to offset the rise in systemic pressure. This option aligns with the established renal autoregulation mechanism.
Option 2: Vasodilation of the afferent arteriole, leading to a decreased glomerular filtration rate. Vasodilation would increase blood flow into the glomerulus and tends to raise, not decrease, GFR. Moreover, it would worsen the pressure gradient rather than stabilize it, making this option incorrect for the described scenario.
Option 3: Vasodilation of the efferent arteriole, leading to a decreased glomerular filtration rate. Efferent arteriole dilation would reduce resistance downstream, lowering glomerular capillary pressure and potentially lowering GFR, but dilation of the efferent arteriole is not the primary autoregulatory response to an acute increase in MAP; the key response is afferent constriction to protect the filtration barrier, so this option does not describe the primary mechanism.
Option 4: Vasoconstriction of the afferent arteriole, leading to an increased glomerular filtration rate. Afferent constriction does reduce GFR, not increase it, so this option is inconsistent with the expected outcome during an autoregulatory response to higher arterial pressure.

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