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Overview of the Endocrine System

Author(s): Center for Educational Outreach, Baylor College of Medicine.


The pancreas is one of many organs with both endocrine and exocrine functions. Islets of Langerhans are regions of the pancreas made of clusters of endocrine cells that secrete two major hormones. Each islet has alpha cells, which secrete glucagon, and a population of beta cells, which secrete insulin. Insulin and glucagon are antagonistic hormones that regulate the concentration of glucose in the blood. When blood glucose is too high, insulin is released. This lowers the glucose levels by stimulating all body cells, except those of the brain, to take up glucose from the blood. When blood glucose is too low, glucagon increases glucose concentration by stimulating liver cells to break down glycogen into glucose.