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  #1  
Old 10-21-2012
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Question renal physio Q on osmolality

Q)If the plasma concentration of sodium increases by 20 mEq/L, and plasma blood urea nitrogen concentration also increases by 10 mEq/L, this change will result in :

A. A 20 mEq/kg H2O decrease in effective plasma osmolality

B. A 20 mEq/kg H2O increase in effective plasma osmolality

C. A 10 mEq/kg H2O decrease in effective plasma osmolality

D. A 10 mEq/kg H2O increase in effective plasma osmolality

E. A 40 mEq/kg H2O increase in effective plasma osmolality

F. No net change in effective plasma osmolality

G. A 30 mEq/kgH2O increase in effective plasma osmolality

H. A 40 mEq/kg H2O decrease in effective plasma osmolality


copied from other forum.....
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Old 10-21-2012
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I assume it is in an normal person ... So the osmoreceptors being very sensitive will try to compensate even for a one or two mOsm increase or decrease in osmolrity .. So no change occurs in the end ... ( I get a feeling that I'm wrong though )... FFF
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Old 10-21-2012
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B
Considering no body response
OR
no change
Considering there is body response
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Originally Posted by alice View Post
I assume it is in an normal person ... So the osmoreceptors being very sensitive will try to compensate even for a one or two mOsm increase or decrease in osmolrity .. So no change occurs in the end ... ( I get a feeling that I'm wrong though )... FFF
you got a point

but assume here the fluid hasnt reached renal system for compensatory changes....
it's asking the compensatory changes made in plasma prior to changes by renal system(just testing the concept of osmolarity.....first osmolarity movement changes occurs then the compensation by osmoreceptors takes place in my opinion....
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Old 10-21-2012
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Quote:
Originally Posted by venky2600 View Post
Q)If the plasma concentration of sodium increases by 20 mEq/L, and plasma blood urea nitrogen concentration also increases by 10 mEq/L, this change will result in :

A. A 20 mEq/kg H2O decrease in effective plasma osmolality

B. A 20 mEq/kg H2O increase in effective plasma osmolality

C. A 10 mEq/kg H2O decrease in effective plasma osmolality

D. A 10 mEq/kg H2O increase in effective plasma osmolality

E. A 40 mEq/kg H2O increase in effective plasma osmolality

F. No net change in effective plasma osmolality

G. A 30 mEq/kgH2O increase in effective plasma osmolality

H. A 40 mEq/kg H2O decrease in effective plasma osmolality


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B
urea doesnt produce effective plasma osmolarity (equilibrates between intracellular and extracellular compartments)
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Correct Answer E is right

this question is based on the concept of osmolality changes and about the differences of plasma and effective plasma osmolality...

logically B should be the correct one....but according to usage of formula... E would be the most appropriate one.....

plasma osmolality depends on changes of sodium,glucose and urea...

plasma osmolality = 2 [Na+] + BUN/2.8 + glucose/18


but in effective plasma osmolality urea is not taken into account ,as it freely permeable across the cell membrane

so, effective plasma osmolality= 2[Na+] + glucose/18...

assuming glucose is constant here.........

any change in sodium concentration would increase two fold in plasma osmolality....so 40 mEq/kg H20 increase is seen in plasma osmolality...

found it useful in other forum ...so posted here with different values..

and after this changes occurs,our body compensatory changes begin with baroreceptors or RAA system activation

thanks
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Quote:
Originally Posted by venky2600 View Post
this question is based on the concept of osmolality changes and about the differences of plasma and effective plasma osmolality...

logically B should be the correct one....but according to usage of formula... E would be the most appropriate one.....

plasma osmolality depends on changes of sodium,glucose and urea...

plasma osmolality = 2 [Na+] + BUN/2.8 + glucose/18


but in effective plasma osmolality urea is not taken into account ,as it freely permeable across the cell membrane

so, effective plasma osmolality= 2[Na+] + glucose/18...

assuming glucose is constant here.........

any change in sodium concentration would increase two fold in plasma osmolality....so 40 mEq/kg H20 increase is seen in plasma osmolality...

found it useful in other forum ...so posted here with different values..

and after this changes occurs,our body compensatory changes begin with baroreceptors or RAA system activation

thanks
i guess the equation is used when calculating the plasma osmolarity
when Cl combined with Na is taken into account that is why we multiply Na by 2

in this particular example only Na is givven
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Originally Posted by MedicalExaminer View Post
i guess the equation is used when calculating the plasma osmolarity
when cl combined with Na is taken into account
is it..?..i'm not sure..
but i checked goljan(on page 54)..it didnt mention abt the chloride inclusion........

correct me ..thanks
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Originally Posted by MedicalExaminer View Post
i guess the equation is used when calculating the plasma osmolarity
when Cl combined with Na is taken into account that is why we multiply Na by 2

in this particular example only Na is givven
The eq is used to calc value in body as Cl is there to make ionic balance,

And yes I agree in only infused Na I won't multiply it by 2 .
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Originally Posted by Kabutar111 View Post
The eq is used to calc value in body as Cl is there to make ionic balance,

And yes I agree in only infused Na I won't multiply it by 2 .
ya..i agree with you all....but can you explain me with goljan page 54 in 3rd edition regarding it....i'm confused....

thanks
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Default osmolarity

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Originally Posted by venky2600 View Post
ya..i agree with you all....but can you explain me with goljan page 54 in 3rd edition regarding it....i'm confused....

thanks
here is the piece from kaplan physio
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Originally Posted by MedicalExaminer View Post
here is the piece from kaplan physio
so with whom should we go..either goljan or kaplan?
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go to p4 kaplan physio

i have problem with attaching file
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Originally Posted by MedicalExaminer View Post
go to p4 kaplan physio

i have problem with attaching file
ya got it ..thanks....

so is goljan wrong regarding it..?

and why cant we consider cl also constant here..?

thanks
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naturally as kidney absorbs Na, Cl follows it due to opposite charge and then water follows so it is almost equally absorbed therefore 1 m/mole NaCl gives to osmolar particles so 1m/mole x 2
when u artificialy infuse only 1m/mole Na it dissociates into 1 osmoticaly active particle
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