<P> The pancreas is an endocrine and digestive organ that, in humans, lies in the upper left part of the abdomen . It is found behind the stomach . The pancreas is about 15 cm (6 in) long . </P> <P> Anatomically, the pancreas is divided into the head of pancreas, the neck of pancreas, the body of pancreas, and the tail of pancreas . The head is surrounded by the duodenum in its concavity . The head surrounds two blood vessels, the superior mesenteric artery and vein . From the back of the head emerges a small uncinate process which extends to the back of the superior mesenteric vein and ends at the superior mesenteric artery . The neck is about 2.5 cm long and lies between the head and the body, and in front of the superior mesenteric artery and vein . Its front upper surface supports the pylorus (the base) of the stomach . The neck arises from the left upper part of the front of the head . It is directed at first, upward and forward, and then upward and to the left to join the body; it is somewhat flattened from above downward and backward . On the right it is grooved by the gastroduodenal artery . The body is the largest part of the pancreas and lies behind the pylorus, at the same level as the transpyloric plane . The tail ends by abutting the spleen . </P> <P> The pancreas is a secretory structure with an internal hormonal role (endocrine) and an external digestive role (exocrine). The endocrine part is composed of hormonal tissue distributed along the pancreas in discrete units called islets of Langerhans . Islets of Langerhans have a well - established structure and form density routes through the exocrine tissue . The exocrine part has two main ducts, the main pancreatic duct, and the accessory pancreatic duct . These drain enzymes through the ampulla of Vater into the duodenum . </P> <P> The upper margin of the pancreas is blunt and flat to the right; narrow and sharp to the left, near the tail . </P>

Where does the pancreas secrete digestive enzymes into