The human body turns food into sugar, and then transports that sugar around in the blood to the cells that need it for energy. Sugar homeostasis refers to the way that the body constantly keeps the level of blood sugar within safe limits. Various hormones in the body act together to control sugar concentration, such as insulin and glucagon, and when these hormones do not do their job properly, illness like diabetes may develop.
Food comes in various forms, from carbohydrates to fats to protein. As the preferred molecule for energy in the body is glucose, the body breaks down food to produces glucose from the useful breakdown products of carbohydrates. Glucose is one type of sugar molecule, which is why it is often referred to as sugar. All parts of the body are able to use glucose for energy, whereas protein and fat is not suitable for red blood cells or cells in the brain.
Glucose is a very important molecule in the human body's metabolism. Complex mechanisms have evolved to ensure that the production, use, and circulation of glucose is safeguarded as much as possible. This safeguarding and regulatory mechanism is sugar homeostasis, and it involves many different substances, which interact with each other.
Insulin is one of the most important substances in sugar homeostasis. The body can only have a certain range of sugar concentration moving around in the blood for health reasons, and when the level gets too high, insulin helps collect up excess sugar and stores it. Glycogen is the storage form of glucose, and insulin helps produce this from glucose in the liver and the muscles. When blood glucose levels drop too low, on the other hand, the sugar homeostasis mechanism needs to boost up the circulating sugar in order to supply the cells of the body with enough energy to run on. Another hormone, called glucagon, acts in the opposite way to insulin, and helps transform glycogen back into glucose to raise blood sugar.
Both insulin and glucagon are produced by the pancreas, and as well as these two major hormones, a variety of other substances have an effect on sugar homeostasis. These include molecular signals from the digestive system which inform the body about the intake of food, and growth hormones which help tell the body where new cells are to be built, and where extra energy needs to go. Certain situations, such as those of danger, also produce signals like adrenaline, which can alter the blood glucose level in order to have more energy available for running away from danger, for example. All of these substances, however, help boost sugar levels, whereas insulin is the only hormone that reduces blood sugar.