A gland in vertebrates lying between the duodenum and the spleen. Under the influence of the hormone secretin it secretes pancreatic juice containing bicarbonate ions, which neutralize the acidity of chyme entering the duodenum from the stomach, and digestive enzymes or their precursors (trypsin, chymotrypsin, amylase, lipase, nuclease, and carboxypeptidase). This mixture is discharged into the duodenum via the pancreatic duct (see acinus). The pancreas also contains groups of cells—the islets of Langerhans—that function as an endocrine gland, producing the hormones insulin and glucagon, which regulate blood sugar levels.