Insulin is an endocrine hormone which is secreted by the pancreas. Its purpose in the body is to store excess glucose in the liver, as well as the muscle tissue as a substance known as glycogen. This is sometimes called animal starch. When the body needs it, it can be converted back to glucose once again and utilized for obtaining energy. The storage of excess glucose prevents a dangerous level of glucose in the circulating blood which can be toxic to the body and upsets homestasis. Another function of insulin is its presence inhibits the secretion of glucagon, and thus prevents the body from using fat as an energy source. This is known as a negative feedback loop.