Test your knowledge #13! (Biochemistry) - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 02-16-2011
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 590
Threads: 31
Thanked 1,227 Times in 410 Posts
Reputation: 1251
Arrow Test your knowledge #13! (Biochemistry)

Because he cannot find enough food for himself and his younger sister, a 14-year-old Haitian boy attempts to prepare a meal from unripe Ackee fruit. He and his sister are found hours later by other refugees, who transport them to a rural aid station. The patients present with frequent vomiting and intermittent loss of consciousness in the sister. The toxin in Ackee fruit converts carnitine and coenzyme A into nonmetabolizable esters, effectively shutting down long-chain fatty acid oxidation. The lack of substrate inhibits gluconeogenesis, leading to hypoglycemia. Gluconeogenesis becomes the main source of blood glucose after approximately ___ hours of fasting.
  1. 2
  2. 8
  3. 12
  4. 24
  5. 30
  6. 48
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (02-17-2011), apx85 (02-17-2011), conspicous (02-17-2011), drgabroomunda (03-04-2011), Drmotivation (02-17-2011), drnirajmavani (02-17-2011)



  #2  
Old 02-16-2011
USMLE Forums Addict
 
Steps History: 1+CK+CS
Posts: 149
Threads: 13
Thanked 46 Times in 34 Posts
Reputation: 56
Send a message via AIM to absolutjag9
Default

is it 24 h?
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-17-2011)
  #3  
Old 02-16-2011
USMLE Forums Veteran
 
Steps History: 1+CK+CS
Posts: 244
Threads: 16
Thanked 198 Times in 86 Posts
Reputation: 208
Default

gr8 question dude. i think the NBME is keeping an eye open for poaching you!


is it around 8 hours.. like when hepatic glycogen dissappears...or was that just 2.. id
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-17-2011)
  #4  
Old 02-16-2011
USMLE Forums Scout
 
Steps History: ---
Posts: 95
Threads: 30
Thanked 33 Times in 27 Posts
Reputation: 43
Arrow C is the answer!

I think the answer is C (12 hrs)...but I am not sure!
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-17-2011)
  #5  
Old 02-16-2011
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,175
Threads: 38
Thanked 852 Times in 478 Posts
Reputation: 862
Default

Quote:
Originally Posted by noone_123i View Post
I think the answer is C (12 hrs)...but I am not sure!
I'd lean towards 12 hours aswell. This would be when plasma glucose would start to fall, and gluconeogenesis would begin.

(Perhaps the reason why PPBG is done after 12 hours?)
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-17-2011)
  #6  
Old 02-16-2011
USMLE Forums Guru
 
Steps History: Not yet
Posts: 298
Threads: 45
Thanked 713 Times in 210 Posts
Reputation: 723
Default

I believe it is 30h, this is when glycogen stores are completely depleted in the starving state
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-17-2011)
  #7  
Old 02-17-2011
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 487
Threads: 95
Thanked 1,458 Times in 356 Posts
Reputation: 1468
Arrow C) 12

Gluconeogenesis is quite active after about 10-12 hours after the last meal. So, I'll go with the closest number 12.
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-17-2011)
  #8  
Old 02-17-2011
USMLE Forums Scout
 
Steps History: Not yet
Posts: 10
Threads: 2
Thanked 5 Times in 5 Posts
Reputation: 15
Default

I also think the answer is C 12 hrs
For this we must understand when the body utilizes fuel stores. For example Creatine phosphate will be the primary source of energy for 3 to 4 seconds. After this is depleted glycolysis starts. After an extended time period (not sure exactly) Gluconeogenesis takes place. Lastly Lipolysis takes over. (Information reviewed in Kaplan Q Book)
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-17-2011)
  #9  
Old 02-17-2011
USMLE Forums Guru
 
Steps History: Not yet
Posts: 298
Threads: 45
Thanked 713 Times in 210 Posts
Reputation: 723
Default

Great question Mondoshawan! We have a test on Endocrine/Nutrition tomorrow and this was actually a point of confusion for me.

Could you please post an explanation, it would really help me for the test!
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-17-2011)
  #10  
Old 02-17-2011
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 590
Threads: 31
Thanked 1,227 Times in 410 Posts
Reputation: 1251
Arrow D. 24 hours

The correct answer is 24 hours. This is a tricky question, because the timeline has so many elements, and because a question could be worded so many different ways to ask for different answers.

Test your knowledge #13! (Biochemistry)-da5c24ff10.png
click image to enlarge
from Lippincott's


2 hours after ingestion of dietary carbohydrates, blood glucose levels return to the fasting state range, stimulating a burst of glycogenolysis. It's true that by 12 hours, gluconeogenesis is quite active (in parallel, ketogenesis kicks in once glucuneogenesis is going strong), but glycogenolysis is also still very active. Around 16 hours of fasting, the glycogenolysis and gluconeogenesis curves cross that is to say, they contribute about equally to the maintenance of blood glucose. By the 24-hour mark, gluconeogenesis is the main source of glucose. By 30 hours after a meal, liver glycogen stores are largely depleted, and gluconeogenesis becomes the only real source of blood glucose. The human body is able to fast for weeks and even months, given adequate stores of fat and intake of necessary non-carbohydrate nutrients.
Reply With Quote Quick reply to this message
The above post was thanked by:
abdul.rehman (02-18-2011), aktorque (02-17-2011), Amenah (02-17-2011), apx85 (02-17-2011), cool_atomic (02-19-2011), donofitaly (02-18-2011), drgabroomunda (03-04-2011), Drmotivation (02-17-2011), FrontalBossing (02-17-2011), malarneela (02-17-2011), manin (02-17-2011), orfie25 (02-18-2011), patelMD (02-17-2011), prataptetali (02-17-2011), TAAOM (03-19-2011), wam_256 (02-20-2011)
  #11  
Old 02-17-2011
USMLE Forums Guru
 
Steps History: Step 1 Only
Posts: 487
Threads: 95
Thanked 1,458 Times in 356 Posts
Reputation: 1468
Arrow

hhhmmmm!!! That was tricky. If the qn asked about the peak time of gluconeogenesis then I'd ans 24hrs. Anyway, Thanks for the qn and your excellent explanation. I'm leaning new things from you. Keep it up doc.
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-17-2011)
  #12  
Old 02-17-2011
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 590
Threads: 31
Thanked 1,227 Times in 410 Posts
Reputation: 1251
Default

Quote:
Originally Posted by aktorque View Post
hhhmmmm!!! That was tricky. If the qn asked about the peak time of gluconeogenesis then I'd ans 24hrs...

Yeah - or " a major source" for 8 or 12 hours, or I guess "the primary source" could have been 24 or 30 - definitely a trick of the words for a question like this... I hope that the USMLE is a little more merciful or less picky than we are in challenging each other!
Reply With Quote Quick reply to this message
The above post was thanked by:
aktorque (02-17-2011)
  #13  
Old 02-17-2011
USMLE Forums Scout
 
Steps History: Not yet
Posts: 10
Threads: 2
Thanked 5 Times in 5 Posts
Reputation: 15
Default

In questions like these it's always good to go with the "Hunch" at first I thought it was D 24 hrs, but I had read something like this a few weeks ago and looked for it and I changed my mind and thought it was C 12hrs.
Apparently the first thing that comes to mind 95% of the time is right!
Reply With Quote Quick reply to this message
The above post was thanked by:
Mondoshawan (02-17-2011)



Reply

Tags
Biochemistry-, Figures-, Step-1-Questions

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Test your knowledge! Mondoshawan USMLE Step 1 Forum 14 01-20-2012 07:34 PM
Test your knowledge #11! (Immunology) Mondoshawan USMLE Step 1 Forum 5 02-15-2011 10:09 AM
Test your knowledge #10! (Pathology) Mondoshawan USMLE Step 1 Forum 4 02-14-2011 08:10 PM
Test your knowledge#4! (Biochemistry) Mondoshawan USMLE Step 1 Forum 9 02-11-2011 03:30 PM
Test your knowledge #8! (Anatomy) Mondoshawan USMLE Step 1 Forum 9 02-11-2011 06:43 AM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)