The document discusses the pancreas and pancreatic islets. The pancreas is a large gland that secretes hormones and is part of both the endocrine and digestive systems. It contains clusters of cells called pancreatic islets (islets of Langerhans), the main cells of which are beta cells that secrete insulin, alpha cells that secrete glucagon, and delta cells that secrete somatostatin. These hormones work to regulate blood sugar levels. The pancreas is located in the abdomen behind the stomach and produces enzymes to aid in digestion.