In the pancreas, there are "islands" of cells scattered throughout. They are richly supplied with vessels and include specialized cells that produce insulin and glucagon. Insulin is probably one of the most famous hormones because of the relative prevalence of diabetes. Read the section on the Endocrine Pancreas in the chapter that focuses on the pancreas. (Gartner and Hiatt pp 418-420).
Insulin lowers blood glucose by stimulating cells to take it up. Glucose is available to cells as a vital food source, to support the cells' energy needs. It is the only major food source for the brain and individuals will pass out if their glucose levels drop.
If glucose drops, insulin levels rise. If glucose levels rise, insulin levels drop. Glucagon has an effect opposite to that of insulin. This hormone will raise glucose and its actions also have a negative effect on insulin (it lowers insulin).
Below is a light microscopic photograph of the endocrine island in the pancreas. It is the cluster of pale cells just below the lettering (Islet of Langerhans). The surrounding cells are clusters of pancreatic cells that make digestive enzymes. These are exocrine gland cells; they secrete their enzymes into a duct that eventually leads to the small intestine.
The Insulin producing cells are blue-purple cells scattered throughout the island. The glucagon producing cells are reddish.
In the above figure, the Islet of Langerhans contains clusters of insulin producing cells. These are called "beta cells". The reddish glucagon-producing cells are not seen as well in this view.
Insulin dependent (Type I) and non-insulin dependent (Type II) diabetes are among the most famous endocrine diseases. The type I diabetes usually has its onset during childhood. In this type, circulating insulin is virtually absent and the pancreas beta cells fail to respond to any stimuli. This disease may result from an infection or a toxic insult to the pancreas. It may be the result of the person's immune system actually destroying the pancreatic beta cells while they fight the infection. While Type I does not appear to be inherited, there may be a genetic predisposition to developing the disease. About 85% of Type I diabetics have circulating autoantibodies to Islet of Langerhans' cells. Many antibodies are directed against a particular enzyme made by insulin producing cells.
Type II diabetes is also called non-insulin dependent. It may be controlled by diet and exercise alone, especially in early stages. This type tends to be linked to obesity and this condition can bring out the Type II diabetic state. Obese individuals develop a resistance to insulin, so that blood glucose is not taken up by the cells . Only about 15% of Type II diabetics are non-obese individuals. The defect may be in the insulin receptor. There may actually be subtypes of type II diabetes. Also, there may be genetic defects associated with Type II diabetes. It can be inherited, especially if both parents pass on the gene. If only one parent passes on the gene, then other factors may intervene, like obesity. So, if you have diabetes in your family, you can prevent onset by eating right and exercising.
