Duodenum and pancreas
The graphic shows the structure of the duodenal wall. From inside to outside, there are the mucosa, submucosa, muscularis (with inner circular and outer longitudinal muscular layer), and serosa. The duodenum is about 30cm ("twelve fingers") long and is the beginning of the small intestine, directly following the gastric pylorus. The head of the pancreas lays in the duodenal loop. The excretory ducts of gall bladder and pancreas, the common bile duct (ductus choledochus) and pancreatic duct, end in the small intestine via the major duodenal papilla. The pancreatic duct transports the exocrine (digestive) secretions of the pancreas into the duodenum, while the endocrine part of the pancreas produces insulin and glucagon. It`s the most important digestive gland.