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Now we'll continue our journey along the gastro-intestinal tract by looking at the small intestine. The small intestine consists of the duodenum and the jejuno-ileum.

The duodenum is the first part of the small intestine. It's also the hardest to see because there's so much in front of it. To see it we'll go to a dissection in which the lower ribs, which were here, have been removed. We've also removed the left lobe of the liver, the greater omentum, and the colon.

This is the duodenum. It begins here, and ends here. The duodenum is partly hidden by the root of the mesentery, which is the peritoneal attachment of the jejuno-ileum. To see all of the duodenum, we'll remove the mesentery, and the jejuno-ileum.

The duodenum starts at the pylorus by passing upwards and to the right, then turns to run in almost a full circle, ending here at its sharply angled junction with the jejunum, the duodeno-jejunal flexure. The discoloration up here is due to post-mortem staining from the nearby gall bladder.

The duodenum is often described as having four parts, numbered one through four. The inner aspect of the curve of the duodenum is largely occupied by this structure, the head of the pancreas, which we'll see later.

The pancreatic duct or ducts, which lie within the panreas, together with the common bile duct, join the second part of the duodenum, as we'll see.

The duodenum lies further to the back than any other part of the gastro-intestinal tract. It's there as a result of an important process that happens in the embryo, the rotation of the midgut. To understand how that happens, we'll look at another extremely simplified animation.