The pancreas is a large gland that lies alongside the stomach and the small bowel. It is about six inches (approximately 15 cm) long and is divided into the head, body and tail.
The pancreas carries out two important roles:
The pancreas produces hormones in its 'endocrine' cells. These cells are gathered in clusters known as islets of Langerhans and monitor what is happening in the blood. They then can release hormones directly into the blood when necessary. In particular, they sense when sugar (glucose) levels in the blood rise, and as soon as this happens the cells produce hormones, particularly insulin. Insulin then helps the body to lower blood glucose levels and 'store' the sugar away in fat, muscle, liver and other body tissues where it can be used for energy when required.
The pancreas is very close to the stomach. As soon as food is eaten, the pancreas releases digestive enzymes into the bowel to break food down. As the food is digested, and nutrient levels in the blood rise, the pancreas produces insulin to help the body store the glucose (energy) away. Between meals, the pancreas does not produce insulin and this allows the body to gradually release stores of energy back into the blood as they are needed.
Glucose levels remain very stable in the blood at all times to ensure that the body has a steady supply of energy. This energy is needed for metabolism, exercise and, in particular, to fuel the parts of the brain that 'run' on glucose. This makes sure that the body doesn't starve between meals.