The endocrine portion of the pancreas consists of numerous small clusters of cells called islets of Langerhans or, more simply, islets. Humans have roughly one million islets.

Alpha cells (A cells) secrete the hormone glucagon.

Beta cells (B cells) produce insulin and are the most abundant of the islet cells.

Delta cells (D cells) secrete the hormone somatostatin, which is also produced by a number of other endocrine cells in the body.

Islets are richly vascularized - though comprising only 1-2% of the mass of the pancreas, they receive about 10 to 15% of the pancreatic blood flow.

They are also innervated by parasympathetic and sympathetic neurons, and nervous signalscan modulate the secretion of both insulin and glucagon.