What is really going on in my body when I am high / low?

Hey all,

today I have a question regarding what is going in the body of a diabetic person when they have a Low vs when the blood sugar is high...

So as I understand it, as a Type 1 diabetic, when I dont inject myself with insulin, my cells dont get the glucose they need for fuel because the glucose remains in the blood stream, which makes my BS levels high. My symptoms then would include feeling tired, dizziness etc...
If I inject TOO MUCH insulin, my BS number drops low, because all that glucose is taken from my blood into my cells, my symptoms would include shaking, light headedness and ultimately I would faint.
Now my question: If I DONT inject the insulin I need, my cells are not getting the glucose they need, so isnt that really a "low" because my cells are running on too little fuel, therefore shouldnt I also feel the low symptoms – a classic example would be that my brain isnt getting the glucose it needs (because the lacking insulin doesnt deliver the glucose into my cells) and isnt that why when low, I ultimately faint?
So why is a "high" not really a "low" – since in both scenarios my cells end up with too little glucose to work with and give me energy?
Or are the symptoms my body gives me a result of what is going on in my BLOOD STEAM, not in my CELLS?

It seems I havent really understood the true mechanisms of what is going on during a high and a low quite yet...Maybe someone can explain it to me?
Would be HIGHly appreciated ;)

I've only noticed lows affecting my head but highs seem to affect all sorts of things. Not only does your brain get fuzzy because there's no energy in the cells but things that seem to require precisely calibrated blood seem to get it the worst...eyes, extremities, kidneys, etc. Maybe too places with smaller vessels get clogged from the sludgy blood? I don't run high very often (211 now though, eeek!) so I'm not as familiar with that but I'm familiar enough with it to know that it's bad, if that makes sense.

The terms Hyperglycemia and Hypoglycemia refer to the amount of glucose in the bloodstream, not the cells. So you were correct when you said that the symptoms you get when your high or low are a result of what is going on in the blood. The symptoms varies from person to person and from event to event.

I know when I'm high, I get severe cottonmouth, which I always thought was my body's way of telling me to drink more to dilute the amount of glucose in my blood. When I'm low, I get shaky and light-headed, which was my body's way of telling me I need energy from food (read; my blood needs more glucose).

Untreated T1D is ultimately the body in starvation mode. The body starts to process fat and then muscle for fuel (since it can't get sugar into the cells) resulting in ketoacidosis (ketones are a byproduct of fat metabolism, thus even when our BG is normal, if we are starving, ketones can increase, obviously magnified in the long-left-untreated T1D - severe undernourishment). Furthermore, the brain can adapt in this case, using the ketones mainly for fuel. I believe, when glucose is in the brain cells, but it is sensed that more is not available in the bloodstream (i.e. LOW BG), the brain will shut down (i.e. one may faint) - this is a protective mechanism to keep our other organs running in time of need. Whereas in untreated T1D, while it's true that the brain cells struggle to utilize the sugar (at least in the insulin-mediated sense), they in fact can sense that sugar is available so the "fainting mechanism" is not activated, because the brain cells "think" they have plenty of sugar in their environment.

I'm by no means an expert on this. I am a cell biology Ph.D. student, and this is what I remember from Undergrad Biochemistry... Hope it helps!

I think passing out from a low is partly because our bodies don't match the physical state of how things are "supposed" to be. My understanding was that ketones are only produced when there is a low insulin level. So they are produced when our BG is high (because there is lack of insulin) and ALSO when BG is low (for normal people), as the pancreas stops producing insulin if BG drops low. In this case, in either state, your brain could run off ketones.

But, for those of us with Type 1, there is too much insulin when we are low (which causes the low), and there is no way of "shutting off" the insulin that is there. Therefore, no ketones can be produced (at least as long as there isn't some other factor, like we haven't eaten for days), and therefore our brain has nothing to run off of.

Most of the symptoms of a low like shakiness, sweating, hungriness, and so on are caused by the hormones that our body releases to try and raise blood sugar levels. This is why anyone, with or without diabetes, can get these symptoms. But my understanding is that it's very rare for someone without diabetes to get brain-related symptoms of a low, like confusion, weird visual and auditory effects, numbness in the mouth or all over, and loss of consciousness. For most people without diabetes or some other condition that causes them to abnormally produce too much insulin, they will never reach a dangerously low blood sugar level, even though they can go low.

I am no doctor or scientist, so someone please correct me if I am totally wrong, but this is how I would assume lows work.

The “low” refers to the level in your blood not the levels in your cells. Interestingly, brain cells do not require insulin to consume glucose, but they do require glucose of a certain level to function correctly… Hence the fainting, etc when blood gluccose drops too low. Your first assumption is correct that your immediate symptoms are based on blood glucose levels. Longer term symptoms such as unexplained weight loss, etc, could be attributed to he cells in your body having been unable to consume much glucose-- I’m not sure though if referring to them as “low” would be correct or not

The reason your brain gets foggy when you have a low but not a high is because the brain is the only part of the body that does NOT require insulin to get at the sugar. Your brain runs on pure glucose no insulin needed. When the sugar is high your brain has plenty of sugar because it doesn’t require insulin. When its low and your confused, it because there is no pure glucose in the body for the brain

I forgot about this. I think this makes my explanation above completely wrong. :)

I do wonder sometimes why the entire body can't run off pure glucose? It would make things easier, I would think.

From wiki reference, validated by memory: http://en.wikipedia.org/wiki/Glucose_transporter)

There are 4 glucose transporters, but only one of them (GLUT4) responds to insulin signaling. So GLUT4 increases in response to insulin (GLUT4 is in muscle and fat cells mainly). The neurons actually have GLUT3, which has "both a higher affinity for glucose and at least a fivefold greater transport capacity than GLUT1, GLUT2 and GLUT4, which is particularly significant for its role in neuronal glucose transport, where ambient glucose levels are fivefold lower than in serum": http://en.wikipedia.org/wiki/GLUT3

As noted, GLUT3 does not respond to insulin. So when the blood glucose level is high but no insulin is present, the brain cells should be able to still utilize the glucose...

With respect to ketones, I did some searching, this is a good article:

Importantly, it states: " Unlike most other tissues, the brain cannot utilize fatty acids for energy when blood glucose levels become compromised. In this case, ketone bodies provide the brain with an alternative source of energy, amounting to nearly 2/3 of the brain's energy needs during periods of prolonged fasting and starvation." So this would actually be in the case of actual starvation, with respect to Brain using ketones. Because GLUT3 is the main neuronal transporter, in untreated T1D (or HIGH BG) the brain would still use sugar. In a "normal" individual, the ketones would be used by the brain during starvation....

If for some reason a T1D individual has LOW BG along with ketones, the brain would then also utilize the ketones (although with T1D ketones typically are associated with HIGH BG)..

Hope this clears it up a little more :)

Sorry - **NOT true when I said that "in untreated T1D, while it's true that the brain cells struggle to utilize the sugar (at least in the insulin-mediated sense)" See explanation below about Glucose Transporters (GLUTS).

:D Thanks!