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#1
02-04-2012
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Calculation of Plasma Volume?

The rapid ingestion of 1200 mL of water will cause the plasma volume to increase by how many mL?

A. 720 mL
B. 480 mL
c. 400 mL
D. 100 mL
E. 50 mL

#2
02-04-2012
 USMLE Forums Master Steps History: Not yet Posts: 928 Threads: 17 Thanked 539 Times in 375 Posts Reputation: 549

Ans C ........ 1/3 will remain in plasma , as it appears to be pure water , which is not isotonic and will diffuse intracellularly by 2/3 ...
#3
02-04-2012
 USMLE Forums Addict Steps History: Not yet Posts: 101 Threads: 21 Thanked 11 Times in 10 Posts Reputation: 21

Quote:
 Originally Posted by Hitman Ans C ........ 1/3 will remain in plasma , as it appears to be pure water , which is not isotonic and will diffuse intracellularly by 2/3 ...
the answer is actually D I dont know how to derive to it

#4
02-04-2012
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dont know how to get 100 ml either .......
#5
02-04-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 851 Threads: 88 Thanked 710 Times in 380 Posts Reputation: 720

out of 1200ml -1/3rd will be in extracellular and 2/3rd will move into intracellular

1/3rd extracellular =400ml

extracellular is comprised of 1/4th plasma volume and 3/4 interstitial volume

so plasma vol=1/4 multiplied by 400 =100ml

Thanks for the question
 The above post was thanked by: abayan (02-05-2012), Abdulaziz (02-05-2012), docji (02-04-2012), Hitman (02-05-2012), stepdoc1 (02-05-2012), usmle_taker (02-05-2012)
#6
02-05-2012
 USMLE Forums Addict Steps History: Not yet Posts: 101 Threads: 21 Thanked 11 Times in 10 Posts Reputation: 21

Quote:
 Originally Posted by step_enhancer out of 1200ml -1/3rd will be in extracellular and 2/3rd will move into intracellular 1/3rd extracellular =400ml extracellular is comprised of 1/4th plasma volume and 3/4 interstitial volume so plasma vol=1/4 multiplied by 400 =100ml Thanks for the question

thank u very much!!!!
#7
02-05-2012
 USMLE Forums Guru Steps History: Not yet Posts: 414 Threads: 30 Thanked 87 Times in 70 Posts Reputation: 97

Quote:
 Originally Posted by step_enhancer out of 1200ml -1/3rd will be in extracellular and 2/3rd will move into intracellular 1/3rd extracellular =400ml extracellular is comprised of 1/4th plasma volume and 3/4 interstitial volume so plasma vol=1/4 multiplied by 400 =100ml Thanks for the question

Sorry to disappoint , but rule is 2/3 and 2/3 ,intracellular and interstitial respectively (source Kaplan physiology chapter 1) exact answer 133 taking rough round off goes to 100.
Correct me if I am wrong.
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#8
02-05-2012
 USMLE Forums Master Steps History: Not yet Posts: 928 Threads: 17 Thanked 539 Times in 375 Posts Reputation: 549

Quote:
 Originally Posted by Kabutar111 Sorry to disappoint , but rule is 2/3 and 2/3 ,intracellular and interstitial respectively (source Kaplan physiology chapter 1) exact answer 133 taking rough round off goes to 100. Correct me if I am wrong.
well FA says 2/3 and 3/4 for intralcellular and interstitial fluid ...... renal system pg 459 2011 edition ........

the ans is exactly 100 .........
 The above post was thanked by: usmle_taker (02-05-2012)
#9
02-05-2012
 USMLE Forums Guru Steps History: Not yet Posts: 414 Threads: 30 Thanked 87 Times in 70 Posts Reputation: 97

Quote:
 Originally Posted by Hitman well FA says 2/3 and 3/4 for intralcellular and interstitial fluid ...... renal system pg 459 2011 edition ........ the ans is exactly 100 .........
I am doomed another fact difference between two.
Doesn't make difference here but another set of values and I am doomed to be wrong .
Thx for thumbs up
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There is no shortcut to SUCCESS ,and there is no excuse for FALIURE - by Kabutar111
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 The above post was thanked by: usmle_taker (02-05-2012)

 Tags Physiology-, Step-1-Questions

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