 Endocrine glands provide the cardinal example, but specialized cells in various other organs also secrete hormones.Hormone secretion occurs in response to specific biochemical signals from a wide range of regulatory systems.For instance, serum calcium concentration affects parathyroid hormone synthesis; blood sugar (serum glucose concentration) affects insulin synthesis; and because the outputs of the stomach and exocrine pancreas (the amounts of gastric juice and pancreatic juice) become the input of the small intestine, the small intestine secretes hormones to stimulate or inhibit the stomach and pancreas based on how busy it is.