avishkar1984
Forum Junior
Topics: 15
Posts: 58
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the kaplan text states that ketogenolysis occurs in brain only in cases of starvation.....
wat is the possible signal to the brain that the body is starving??
the glucose that it is taking up....(obviously)
well if gluconeogenesis is supplying enough glucose to the brain tissue then why would the brain start using ketones for energy???
the chapter on lipid mobilization states that when ketones are metabolized to acetyl coA, pyruvate dehydrogenase is inhibited and hence glycolysis stops.
true, but why would ketones be metabolized in the first place, when there is sufficient glucose frm gluconeogenesis?
well one might argue that gluconeogenesis is not sufficient to keep up with the energy requirements of the brain.
the kaplan notes further mention that the switch from glycolysis to ketogenolysis is important as it spares the body protein..
and if this is the case then why shd ketogenolysis occur??
so wat it is trying to say is that the brain uses ketones, not because it doesnt have enough supply of glucose, but, because it has to prevent too much of protein from going into gluconeogenesis.
well this implies that there is still enough protein in the body for gluconeogenesis to occur.
so the question arises, wat is the actual signal for ketogenolysis in the brain??
it cannot be starvation as there is plenty of protein for gluconeogenesis.
then wat is it??
i hvnt been able to find out an answer to this..
ppl pls help me out.
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| drduck
Forum Guru
Topics: 82
Posts: 529
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brain utilises ketones only when there is no sufficient glucose present in the body.......including the stored gycogen...
u r correct saying that brain does this in order to avoid protein or in other words muscle break down....
this doesnt mean brain cannot use AA for energy....but, bcos it has ability to convert ketones to produce energy....not glucose....it does that efficiently....
also the brain doesnot wait for whole of body glucose and glycogen stores to get depleted to a level of ZERO....it starts utilising ketones as and when required....
it is not that only at fixed level of Serum glucose it will switch over to ketones.
remeber ketone utilisation never gives glucose to the brain, it just provides energy or ATPs to the brain till sufficient amount of glucose gets available.
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| avishkar1984
Forum Junior
Topics: 15
Posts: 58
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the point is that there is already sufficient amt of glucose available from gluconeogenesis otherwise the brain would stop working
so ur explanation that ketone metabolism is just a way of buying time till glucose becomes available doesnt seem very plausible
but thnx fr the reply neway
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| avishkar1984
Forum Junior
Topics: 15
Posts: 58
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ppl pls help me out
ne other suggestions???
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| SmokyWaters
Forum Elite
Topics: 6
Posts: 458
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its PROLONGED STARVATION that means more than a week...when aminoacids are BURNT out to produce GLUCOSE through gluconeogenesis...
so its that you have to CONCEPTUALIZE the fact which I am goin to tell now...
its true that blood glucose is maintatined by hepatic gluconeogenesis and later kidneys also play a significant role in prolonged fastin...from gluconeogenic precursors such as amino acids provided by rapid breakdown of muscle proteins...
in prolonged fasting, plasma ketone bodies which were produced before as well reach significant ELEVATED LEVELS and are used in addition to glucose as a fuel by the brain...so its just not that GLUCOSE isnt produced at all..its just that KETONES have INCREASED and GLUCOSE has decreased so preferentially thereis more use of ketone bodies...alongwith induction of enzymes for their utilization...
this reduces the need for protein catabolism...which is STILL There ...its not totally SWITCHED off...consider the concept not as concrete as its written in KAPLAN...thats just for explanation...
consider that there is a significant level at which somethings in body are used PREFERENTIALLY over others...
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| avishkar1984
Forum Junior
Topics: 15
Posts: 58
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thnx smokywaters
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