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MedFriends.org Forums > USMLE > USMLE Step 1 > Physiology question I came across. Need help figuring it out...
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Author Topic: Physiology question I came across. Need help figuring it out...  (Read 193 times)
jacko43
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Physiology question I came across. Need help figuring it out...
« on: March 10, 2006, 02:16:07 PM »
A cell is equilibrated in an aqueous soln of 300mOsm/kg NaCl. What will happen to the cell volume when this cell is placed in an aqueous soln of 300mOsm/kg glycerol?
A-Decrease
B- Decrease and then increase
C- increase
D- increase and then decrease
E- No change
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doog
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Re: Physiology question I came across. Need help figuring it out...
« Reply #1 on: April 26, 2006, 10:31:36 PM »
In any osmolarity/osmosis/equilibrium question, you need to ask yourself: is the quoted osmolarity effective or ineffective?

Most books teach all about urea, which is an ineffective osmole.  Why? because it freely crosses cell membranes and exerts no osmotic pressure.

Effective osmoles, then, do not cross the cell membrane.  They tend to be large (albumin) or polar (Na+) molecules.

Glycerol would freely cross the cell membrane, and would be an ineffective osmole.  placing a cell in this solution would be equivalent to placing it in pure water.

The cell will swell.
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jacko43
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Re: Physiology question I came across. Need help figuring it out...
« Reply #2 on: April 28, 2006, 06:45:21 PM »
Great answer!  Thanks!
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