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drazi
Forum Newbie Topics: 14 Posts: 50 |
Q- A solution contains 300mosm NaCl and 100mM Urea. What is the tonicity and osmolarity compare e RBC having osmolarity of 300mosm/L? What i have figured out is that the osmolarity is 400mosm....this means it is hyperosmotic Tonicity is the total conc of nonpenetrating solute which is in this case 300 so the solution is isotonic..... but what if there is urea...it is permeable and enters the cell with water and the cell swells... SO IS IT GOING 2 B ISOTONIC or HYPOTONIC? im confused here....can some1 provide good explanation and correct?
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drazi
| Forum Newbie Topics: 14 Posts: 50
plz somebody explain this? why does it say in kaplan Q tht in the presence of urea the cell swells???????
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wishikhan
| Forum Newbie Topics: 93 Posts: 278
osmolarity refers to non permeable solutes .which are sodium chloride and glucose in hyperglycemia . tonicity refers to the effect on cell size not to the concentration of solutes . urea is easily permeable to the cell wall doesnot contribute to the osmolarity . so the total osmolarity is 300 so its isoosmotic. plus isotonic no change in size simple explanation of isotonic loss of fluid means equal loss of sodium and water eg in diarrhea you have simply vice versa the made i hope i understand what i have written
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coolraks
| Forum Newbie Topics: 0 Posts: 16
good question drazi... n a decent xplanation wishikhan... i jus hav a slight more xplanantion to offer... 1stly it is not osmolarity... but osmolality to be specific... the whole solution is hyperosmolar by itself COMPARED to blood(300mOsm) but the OSMOTIC EFFECT is due to non penetrable solutes, in this case sodium... but REMEMBER- this solution doesNOT hav only 300mOsm of Na, in tht solution u hav added 100mOsm of urea (which has no osmotic effect onthe movemnt of water into or out of the cell) so wen u add 100(or even 200, 300 etc mOsm of urea) it is equal to adding pure water into the Na solution, therfore makin the solution hypotonic(or reduced osmotic effect on a cell) so tonicity is simply the effect of non-penetrable solutes on cell size or volume... n unlike wt wishikhan says, it is not really vice versa of losing isotonic water... i hope my xplantion makes ur concept clear...if it does do gime a feedback drazi 
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coolraks
| Forum Newbie Topics: 0 Posts: 16
so although tht solution per se is hyperosmolar, but has a hypotonic effect on RBCs... anothr question on similar lines... a solution havin 400mOsm of Na, and 200mOsm of urea... wt wil its effect b? Ans, we dont kno... as , altho it is hyperosmolar, Na being 4oo, makes it hypertonic seemingly, but ur adding water (in the form of urea) so se either make it isotonic with blood or hypotonic to blood.. we at this level dont kno the formula for this kind of calculation, so we cant calculate
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drazi
| Forum Newbie Topics: 14 Posts: 50
To coolraks...thnx a lot for replying...i m trying to get my concept clear...u have given good explanation...will go thru the chp once again to clear it completely...but why did wishikhan write isoomotic to the question i asked isnt it hyperosmolar( the soultion)???
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