Blood sugar level several interacting systems, of which hormone regulation is the most important. There are two types of mutually antagonistic metabolic hormones affecting blood glucose levels: These hormones are secreted from pancreatic islets which are bundles of endocrine tissues. There are four types of pancreatic islets, alpha (A) cells, beta (B) cells, Delta (D) cells and F cells. Glucagon is secreted from alpha cells, while insulin is secreted by beta cells. Together they regulate the blood-glucose levels through negative feedback, a process where the end product of one reaction stimulates the beginning of another reaction. In blood-glucose levels, insulin lowers the concentration
Corpuscle of Stannius composed of several columnar cells, which contain secretory granules and are, thus, secretory in function. Each Secretory granule is spherical in shape and measures 0.5 to 1 μm in diameter. Their possible endocrine nature, i.e. producing hormone, was suspected from the complete anatomical description, and it was believed to be responsible for regulating calcium level in the blood. The hormone was identified as stanniocalcin. Bony fishes obtain calcium directly from their aquatic surrounding (unlike other vertebrates which acquire from diet), so that they require separate endocrine organ. The corpuscles of Stannius are the sites of production of the hormone called