Doctors or Med students in the house?

[Pohemi]

From my understanding, ketones are a type of acid produced when your body starts using muscle tissue for fuel instead of fat. After extended periods of blood sugars above normal, ketones start to become present in the blood and urine.
My question is: When your blood sugar is high and your liver keeps pumping out glucose because there is not enough insulin present to allow the sugar in your bloodstream to enter your tissues where it's needed, why does your body start burning(using) muscle tissue for energy?

 

[Gibsons]

cells do a poor job of taking up glucose in the absence of insulin. Lacking glucose, they resort to burning protein and/or fat.

 

[Pohemi]

Originally posted by: Pohemi420
...your liver keeps pumping out glucose because there is not enough insulin present to allow the sugar in your bloodstream to enter your tissues where it's needed, why does your body start burning(using) muscle tissue for energy?

Originally posted by: Gibsons
cells do a poor job of taking up glucose in the absence of insulin. Lacking glucose, they resort to burning protein and/or fat.

Ok well thanks for basically repeating what I just said, but do you know why your body resorts to burning muscle(protein) instead of fat in the absence of glucose/ATP's? Ketones are produced by protein consumption, not the typical useage of fat that the body does normally.

 

[Gibsons]

going from memory, so apologies if I slip up...

The ketones in the blood are (most likely) from the liver. In conditions of high fat oxidation (ie diabetes), the liver can produce ketones from fats, from some sort of beta-oxidation/acetyl CoA reaction.


edit
(can open up the biochem books and give more detail if this doesn't get at what you're asking.)

edit 2: don't forget the ketone bodies are small slightly hydrophobic molecules. Which means they can probably diffuse across cell membranes pretty easily. So if most all cells are making them (regardless of source), they'll show up in the blood just from diffusion.

 

[Pohemi]

Well I remember a little bit about ketones from adv. biology in high school...but most of my knowledge about it comes from being a diabetic for 21 yrs myself. My doctor was the one who had described to me how absence of insulin led to sugar being trapped in the blood stream. Since your involuntary systems don't realize this, your brain tells your liver to pump out even more glucose. It becomes a vicious cycle, which leads to extreme dehydration and ketoacidosis. My doctor explained that the ketones were a byproduct of your body breaking down protein tissue to use for fuel. I don't remember why but he told me the body eventually stops trying to use fat tissue and just starts burning muscle. The ketones go through your liver AND your kidneys (and can contribute damage by being filtered through these organs), as they wind up in your urine also, but I'm not sure the ketones are actually produced by the liver. I could be wrong...I'm not a doctor myself.
You know the feeling someone might get in their legs if they're not used to running and they go out and run 2 miles? That build up of lactic acid in their leg muscles that burns like hellfire?
Basically ketoacidosis at an advanced stage feels like that....times 10....through your entire body. You feel it in every muscle, even your jaw. It's a pretty sickening feeling. I'm just wondering why your body eventually stops using/burning fat (which is the usual fuel source), and instead switches to burning muscle tissue when it really doesn't do your body any good. Is it maybe like your body's last ditch effort to provide fuel to itself before shutting down?
Left unchecked and untreated, diabetic ketoacidosis will most certainly lead to diabetic coma and then death.

 

[Gibsons]

First, the liver definitely produces ketone bodies no doubt about that (other organs/cells may also).

Generally speaking, I don't think that there are cases where either protein or fat are metabolized exclusively. If glucose isn't available, both will be used to some degree, and both can produce ketone bodies. There's not a big "switch" from one to the other under the conditions we're talking about.

The immediate product of (most) fatty acid metabolism is acetate which is then made into acetyl CoA. Acetyl CoA is the starting point for synthesis of ketone bodies, whether from fat or protein.

 

[Mark R]

To pohemi: You've made a couple of mistakes there.

Ketones are a type of partially digested fat which are used in place of sugar. Normally, the body has a store of glucose (actually it's stored in the muscles and liver as a polymer called glycogen), and this is released when the glucose in the blood starts to fall.

Insulin is the control system that tells the body how much glucose it has, and what energy source to use.

When you eat, high blood sugar causes insulin to be produced. The insulin causes glucose in the blood to go into the muscles and liver where it is stored as glycogen. Without insulin muscles and liver can't absorb the glucose. (Basically, glucose is unable to cross cell membranes on its own. Cells which need glucose have special transporter molecules on their surface which grab glucose molecules and drag them inside. Insulin is needed to switch these on).

When you are hungry, and the body reduces insulin production, the flow of glucose reverses - i.e. out of muscles.

When you are starving, the body virtually stops producing insulin, and glucose reserves continue to be raided. Certain organs (like brain and kidney) can't burn fat - if glucose reserves were to run out, this would be a problem. However, when the body thinks it's starving (very little insulin at all) in addition to glucose flowing from muscles and liver, a second emergency energy supply comes on stream: ketones. Ketones are essentially partially digested fats. They are produced in the liver - and can be burned by vital organs in place of glucose. Small quantities of ketones can be produced in muscles from protein, but the dominant source is conversion of fat by the liver.

So, diabetes is inappropriate loss of insulin - no insulin means the body thinks it is starving, whereas in reality there is so much glucose available it is becoming toxic.

Ketoacidosis can occur in diabetes when there is no insulin produced in the body. Even in starvation there is always a tiny trickle of insulin to keep ketone production in check. Without any insulin, ketone production goes into overdrive and produces toxic quantities of ketones and their related ketoacids.

 

[Pohemi]

Ok thanks, that explains what I wanted to know a little better. :thumbsup:

 

[Taejin]

nevermind.