Homeostasis and Glucose: How It works
Homeostasis is the regulation maintaining a balance of a number of conditions in the body, including but not limited to temperature, water content, sugar, carbon dioxide levels and other. Maintaing homeostasis is essential for long term health because as one of components gets disbalanced it pulls other components behind and so the entire system becomes skewed and finally collapses.
In relation to blood glucose, homeostasis is mostly about the proper balance of insulin and glucagon, the hormones produced by your pancreas to maintain adequate blood glucose levels. These hormones from the so-called negative feedback loop where one counterbalances the other's action. Consistently high blood glucose may result in nerve damage or epileptic seizures. Consistently low blood glucose leaves your body cells starve for energy and may cause you to faint, and at some point the work of a brain deprived of glucose may affect vital fucntions, like breathing and the work of your heart.
Insulin is a hormone secreted by the pancreas when your blood glucose goes up, usually that happens after meals. Ideally, the concentraion of glucose in your blood is 0.001%. When you blood sugar goes above 0.001% your pancreas starts producing insulin necessary for the uptake of glucose by your body cells other than you brain's neurones, such as muscles, and converting in into energy. In reaction to insulin your liver starts converting glucose into glycogen, a starchy sugar type, and stores it, and this process is called glycogenesis. A certain anount of glycogen is also stored in your muscles. When blood sugar stops coming to your blood flow from you digestive system you pancreas stops producing insulin and so you liver stops converting glucose into glycogen.
When your blood glucose drops below 0.001%, usually four to six hours after meals, your body cells stop using the sugar from your blood because pancreas no longer produces insulin. Instead, it starts producing glucagon, a hormone that signals to the liver that it's time to release its glycogen supplies and convert them into glucose to prevent you blood glucose from dropping lower. All the energy from glycogen goes to the VIP user, brain, which does not need insulin for glucose uptake. Why so? You brain is responsible not just for active thinking, solving problems, memorizing or other cognitive taks, concentration etc, but for maintaining basic viral functions in your body, like the work of you heart and blood pressure regulation, breathing, thermoregulation and other. Having energy for constant control of all these functions is critical. On the other hand, too much glucose delivered to your brain cells may damage them or cause epilepcy.
How much glycogen does my liver store?
As a rule, maximun glycogen supplies in your liver are 200-300 g. This amount is enough to supply your brain with energy for 2 days. After that the energy is produced by breaking down fat stored in your body. This is important information for those fighting with excess weight: starving for 2 days won't make you lose any fat. Starving on and losing weight rapidly is dangerous.
What does my liver do with excess glucose?
When glycogen storage capacity of you liver is exceeded (200-300 g) you liver starts transforming glucose into fat.
How do I check my glucose homeostasis?
The ability of your body to maintain glucose homeostasis is checked by means of Glucose Tolerance Test. You will be injected a high amount of glucose and then the doctor will estimate how quickly your body restores normal blood sugar level.
Any other factors or hormones involved?
When your plasma glucose goes down you brain receives a signal and the areas responsible for appetite activate. However, this is not the only regulating factor. As your stomach shrinks your brain receives 'mechanical' signal from collapsing stomach and appetite zones acitvate. Quite recently, ghrelin also called a "hunger hormone" was discovered. This hormone is produced by you stomach and also works as a chemical signal activating appetite zones.
Another involved hormone is leptin. Leptin, also known as a fat-burning hormone, is released by your fat cells when your body has stored enough fat. Now many scientists believe that excess weight is caused by leptin-resistance. The reason is simple: historically humans were more likey to die of starvation than of overeating. For this reason the mechanisms targeted at supplying fat, fetching and storing energy work better. Homeostasis also largely depends on genetic factors.