AAMC explanation doesn't make sense. I need help walking me through how to get the right answer. Why Av/na and not nav/A??
Thank you
AAMC FL3 C/P #52

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Re: AAMC FL3 C/P #52
Thanks for the question!
This is basically an application of the continuity principle: A1V1 = A2V2
In the first case, we have Av for the area and speed of the blood in the capillary.
In the second case, we have na for the total area of the capillaries (total number * volume of each), and then we're looking to solve for velocity (let's follow the AAMC answer choice convention and call it u).
Thus,
Av = nau
Av / na = u = (A/na)v
I hope this helps clarify it!
This is basically an application of the continuity principle: A1V1 = A2V2
In the first case, we have Av for the area and speed of the blood in the capillary.
In the second case, we have na for the total area of the capillaries (total number * volume of each), and then we're looking to solve for velocity (let's follow the AAMC answer choice convention and call it u).
Thus,
Av = nau
Av / na = u = (A/na)v
I hope this helps clarify it!