Pancreas

The pancreas is an elongated organ that generally measures six inches in length and lies sideways slightly below the stomach. As an exocrine organ, the pancreas produces enzymes that influence digestion. The pancreas is a tiny fraction of the organ that is composed of a cluster of hormone producing cells referred to as the islets of Langerhans.

The hormone-producing cells of the pancreas are named for Paul Langerhans. It was Langerhans who in the late 1860s first described the existence of cells within the pancreas that were not connected to ducts. Later scientists discovered that these scattered cells actually operated as an endocrine gland. Estimates of the number of Langerhans' islets occupying a normal pancreas vary, but some go as high as 1 million. You can imagine how small they must be if all together they make up less than 2% of the entire pancreas.

Scientists have identified three types of cells within each of these miniscule islets. They are known as alpha, beta, and delta cells. Delta cells secrete somatostatin, which inhibits the release of growth hormone and the secretion of insulin and gastrin. The beta cells, which comprise approximately 80% of the islets, manufacture and secrete insulin. This hormone helps remove glucose from the blood by binding to receptor cells and increasing its target tissue's ability to take up and use glucose. Glucagon, the hormone produced by the alpha cells, works in direct opposition to insulin-it increases blood sugar. Unlike many of the hormones, neither insulin nor glucagon is controlled by the pituitary gland. Both alpha and beta cells receive signals directly from the circulating blood and the nervous system. With a balance of insulin and glucagon secretions, the body is able to constantly adjust its level of circulating glucose.