we have a lot of mechanisms to save us from starvation, like sensing by mTOR, leptin, and sensing glucose levels. question 1) is there a mechanism to sense that insulin levels are getting too low? what is it? does it work to try to raise insulin levels? maybe there is no mechanism so that is why dka can occur? we do have a mechanism to deal with excess glucose in the blood (peeing it out and getting thirsty). questions 2) why do we have a mechanism for dealing with high blood sugar when having extremely high blood sugar was probably rare during evolution?
As far as I know, no such mechanism exists. Elevated blood glucose levels are the only stimulus to raise insulin levels, I think. Insulin levels probably aren’t useful for the body to measure since they depend on various things like carb intake and activity.
DKA occurs because the body isn’t able to make enough insulin. A mechanism that senses insulin levels wouldn’t help preventing DKA.
I believe this is not so much a mechanism to get rid of excess glucose, but rather the inability of the kidneys to reabsorb excess glucose from pre-urine. Getting thirsty is the natural consequence of this process. As glucose can’t be excreted without water, you constantly need to compensate for the loss of water.
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For what it’s worth, peeing out glucose isn’t super effective at dealing with extremely high blood sugars (just not powerful enough, otherwise you’d eventually come down from most highs on your own), but it does get activated when blood sugars aren’t that high (160-180, depends on the person), and spikes into that range can occasionally occur even for non-diabetics. So while it’s a mechanism that’s in overdrive for extremely high blood sugars, it’s probably at its most effective at taking the edge off temporary minor elevated ones where only a little excess sugar needs to be removed.
Agree with @cardamom. This is not the body’s mechanism to deal with high blood sugar. Rather this is the body starting to fail. Usually the high BG is corrected with insulin whether from pancreas or external so this situation does not have to continue. Without the insulin, the body clearly can not self correct.