Structure and Innervation of the Exocrine Pancreas
The pancreas is a mixed gland. The exocrine part elaborates pancreatic juice, while the endocrine part synthesizes and secretes insulin, glucagon, pancreatic polypeptide, and somatostatin. The exocrine pancreas comprises 98% of the gland. The endocrine pancreas makes up the remaining 2% . The pancreas is characterized by islands of endocrine cells amongst the exocrine pancreas; therefore, the endocrine part is often called the Islets of Langerhans. The 100-gram pancreas synthesizes and secretes about 1.5 L of pancreatic juice per day. The alkaline juice neutralizes the duodenal chyme and contains enzymes for digesting proteins, fats and carbohydrates.
The secretions of the acinar cells that synthesize and secrete pancreatic juice leave the cells via exocytosis (figure). They drain into intercalated ducts, which in turn drain into intralobular ducts, and ultimately drain into the extralobular duct that empties into the duodenum along with the common bile duct. The exocrine pancreas is supplied by blood from the celiac and superior mesenteric arteries.
The pancreas is innervated by preganglionic parasympathetic branches of the vagus that synapse with cholinergic neurons within the pancreas. Sympathetic nerves from the celiac and superior mesenteric plexuses innervate the blood vessels of the pancreas. Sympathetic nerve impulses inhibit and parasympathetic nerve impulses stimulate pancreatic juice secretion.