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Aymeric Aymeric
wrote...
Posts: 7
Rep: 2 0
10 years ago
 Hello,

I'm a dietetics student, and my course is really unclear about gluconeogenesis regulation, and exactly WHEN it happens.

What my coursebook teaches me is that glycogenolysis is the main purveyor of energy during physical exercise, and it is triggered by LOW INSULIN, HIGH GLUCAGON and HIGH ADRENALINE, which is exactly what happens when you start working out. So far so good.

But then they tell me that gluconeogenesis is triggered by LOW INSULIN, HIGH GLUCAGON and HIGH ADRENALINE, so: exactly the same conditions as above. And yet they keep saying throughout the chapter that gluconeogenesis SELDOM occurs during physical exertion itself, and that aminoacids are used only as a last resort, even though they specified a few pages before that the main substrate for GNG is alanine (followed by lactate and glycerol).

So there HAS to exist some factor that apparently delays GNG other than the aforementionned hormones, otherwise both metabolisms would start at the same time since they respond to the same hormonal changes. Right? But there is no mention of any such thing in my course.

I'm lost! If anyone could clear that up for me, I'd be really thankful.
Source  It's a French textbook...
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wrote...
Staff Member
Educator
10 years ago
The process is triggered by glucagon. Glucagon is released when the glucose level in the blood is low (hypoglycemia), causing the liver to convert stored glycogen into glucose and release it into the bloodstream. The action of glucagon is thus opposite to that of insulin, which instructs the body's cells to take in glucose from the blood in times of satiation.
Mastering in Nutritional Biology
Tralalalala Slight Smile
Aymeric Author
wrote...
10 years ago
Thank you padre!

So you too are of the opinion that GNG does start at the same time as glycogenesis?

Why do most textbooks I've come across say that GNG starts only after glycogen is depleted? I agree with you that it doesn't make sense, unless some crucial info is missing.
wrote...
Staff Member
Educator
10 years ago
NP. Not all textbooks are consistent because they're written by different authors.
Mastering in Nutritional Biology
Tralalalala Slight Smile
wrote...
10 years ago
According to Tortora's Principals of A&P, sympathetic stimulation will cause both gluconeogenesis and glycogenolysis in response to glucocorticoids in the blood stream. 

Assuming you are able to generate a sympathetic response to exercise, you will do both, simultaneously, during exercise.  Depending on the level of intensity (stress), levels of cortisol may vary, changing the amount of glucose generated from non-carbohydrate energy sources (preferably protein).

Hope this helps.
Source  Tortora-Principles of Anatomy and Physiology 13th edition
Aymeric Author
wrote...
10 years ago
Thank you both for your remarks.

I am really surprised to see that this issue does not seem to be clear even to authors of recent textbooks...
And the idea that GNG only starts after glycogen is used up seems to be very common among ahtletes (based on the bodybuilding and marathon blogs/sites I have read).
wrote...
Staff Member
Educator
10 years ago
based on the bodybuilding and marathon blogs/sites I have read

Those are terrible reads, especially body-building websites.
Mastering in Nutritional Biology
Tralalalala Slight Smile
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