The pancreas contains exocrine cells and endocrine cell clusters. Exocrine cells secrete digestive enzymes into the small intestines.
Endocrine cell clusters (aka pancreatic islets or islets of Langerhans) secrete insulin and glucagon. Insulin and glucagon regulate blood glucose levels. After a meal, when blood glucose levels rise, insulin is released so that cells can uptake the elevated glucose levels. Liver and skeletal muscles form glycogen, a carbohydrate.
As glucose levels fall, insulin production is inhibited. Glucagon causes breakdown of glycogen into glycose, which is in turn released into the blood to maintain homeostatic glucose levels. Glucagon production is stimulated by low blood glucose levels, and inhibited when they rise.
The pancreas serves as a ductless gland by regulating blood glucose levels:
- When blood glucose levels rise, insulin is released so that cells uptake the glucose and it is removed from the bloodstream. Also, the liver and skeletal muscles store glucose as a carbohydrate named glycogen.
- When blood glucose levels drop, glucagon is released so that the glycogen in liver and skeletal muscles is released as glycose. This maintains homeostatic blood glucose levels.
When blood glucose levels are not properly regulated, diabetes results.
For example, if not enough insulin is produced (or the liver does not properly respond) then blood sugar can rise out of control and the result is diabetes mellitus. Diabetes causes impairment in functioning of eyes, circulation, CNS & PNS, and kidneys; it is the 2nd leading cause of death. The two major types of diabetes are shown below:
- Type I Diabetes involves inadequate levels of insulin secretion, usually from a genetic cause. This results in blood glucose levels to rise, possibly out of control.
- Type II diabetes develops in adults form both genetic and environmental causes. Loss of response of insulin targets rather than lack of insulin causes this.