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Discussion Starter · #1 ·
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.
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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) :)
 

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Discussion Starter · #10 ·
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.

Rectangle Slope Plot Line Triangle

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.
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Discussion Starter · #12 ·
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!:eek:
 

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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. :eek:
Apparently the first thing that comes to mind 95% of the time is right! :rolleyes:
 
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