The two hormones that play perhaps the largest role in controlling the blood sugar (Glucose) level are insulin and glucagon. These two hormones actually work in antagonistic fashions to each other. Another way to think of this relationship is like a ‘Ying and Yang', when one hormone level is high, the other hormone level will be low. The hormone level that is highest depends on what the blood sugar level is. The brain is constantly monitoring the blood sugar level.
When the blood sugar level is high, insulin is in charge. Insulin is released to tell the body to put the excess blood sugar into the tissues. Insulin tells the body to ‘store' the excess sugar in the storage form of glycogen; it also tells the liver cells that make glucose to stop making it. It also tells the liver and fat cells to make fat.
In opposition, when the blood sugar level is low, the hormone glucagon will tell the body storage areas (mostly the liver) to start releasing glucose into the blood stream. The hormone glucagon tells the body to put more sugar into the blood stream by telling the liver to ‘stop listening to insulin and take orders from glucagon'. The result of this is that the storage of glucose stops, fat production stops, and glucose (sugar) is released into the blood stream.
Although these two hormones work in opposite directions, they actually work towards the same goal. The goal of these two hormones is to maintain a level concentration of blood sugar. This ‘stable' level is what the brain likes and allows it to function at its best level. The amazing thing is this is all done without the human consciously knowing that it is going on.