This chapter discusses pancreas, where pancreatic polypeptide plays a role in the regulation of some gastrointestinal secretions. Insulin increases the utilization of glucose and decreases its production. Insulin affects the metabolism of carbohydrates, lipids and proteins, and also stimulates cell division. Food has two basic functions, such as to provide energy and to provide material for growth and repair. Insulin helps in utilization of carbohydrate as fuel to obtain energy. Excessive urinary loss of water activates the mechanism of thirst. Epinephrine and cortisol are stimulated by stress, including that of hypoglycaemia, and bring the plasma glucose back to normal. Excessive loss of water in the urine may lead to some dehydration and disorders of electrolyte and acid base balance. Both glycogenolysis and gluconeogenesis tend to raise plasma glucose level. Insulin resistance may be due to insulin antibodies in circulation, a decrease in insulin receptors, or antibodies to insulin receptors. Glucagon stimulates lipolysis.