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Ammonia is extremely toxic to cells and is kept at very low concentrations by the body. The urea cycle converts ammonia to urea which is nontoxic. Urea contributes to which of the following?
A. Serum osmolality and serum osmotic pressure
B. Serum osmolality but not serum osmotic pressure
C. Serum osmotic pressure but not serum osmolality
D. Neither serum osmotic pressure nor serum osmolality
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sorry raji_321,
I wanted to type "try again" cos D is not the ans.
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hmm.. i thought because urea can cross plasma membrane, it can not contribute to serum osmolality at equilibrium, and because serum osmotic pressure is mainly due to plasma proteins which can not cross capillary memb. i thought D.
plz explain the ans.
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if i have to pick an answer, then B
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Choice (B) is the correct answer. Urea is an ineffective osmole because of its ability to cross cellular membranes. As a result, urea contributes to serum osmolality but does not contribute to serum osmotic pressure. Urea does not contribute to serum osmotic pressure because of its ability to cross cellular membranes. Osmotic pressure results when solutes accumulate that are unable to cross cellular membranes. Increasing concentrations of serum urea levels therefore results in an increase in serum osmolality with no change in osmotic pressure. The other choices are incorrect.
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thanx for nice explanation.
