AAMC B/B Question bank #35

[MC789]

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I crossed out the right answer because I thought that when there increased blood pressure, there is increased blood volume and decreased water in the filtrate -> decreased urine output (this is how Aldosterone and ADH work is what I learnt when studying so I applied this). can someone please explain how increased blood pressure increases urine output? is it because it increases glomerular filtration rate? and why doesn't the reasoning on how ADH works not correct to apply to this question?

 

[pretty_positron]

I crossed out the right answer because I thought that when there increased blood pressure, there is increased blood volume and decreased water in the filtrate -> decreased urine output (this is how Aldosterone and ADH work is what I learnt when studying so I applied this). can someone please explain how increased blood pressure increases urine output? is it because it increases glomerular filtration rate? and why doesn't the reasoning on how ADH works not correct to apply to this question?

I prefer to think about the effects of aldosterone and ADH as being on the concentration of urine, rather than urine output. Since they reduce the amount of water in the urine, the overall volume of the urine decreases but that is really just a side-effect.

Increased blood pressure does result in increased glomerular filtration rate, since that depends entirely on the glomerular hydrostatic pressure (blood pressure) which must be greater than the sum of the oncotic pressure (osmotic pressure of the plasma proteins in the blood of the glomerulus) and the hydrostatic pressure of the bowman's capsule.

The greater this glomerular hydrostatic pressure (blood pressure), the greater the filtration, and thus the greater the overall urine output.