 The top boundary of the abdomen is the diaphragm. When it contracts the lungs are pulled downward and the abdomen becomes smaller. This notch here in its posterior surface allows room for the vertebral column, and there are then two holes in the superior surface of the diaphragm, one for the inferior vena cava and one for the esophagus, which plugs into the stomach here. The stomach is roughly J shaped and as you can see leans back on a slightly oblique angle. It's said to have a greater curvature here and a lesser curvature here. It connects to the duodenum, which is more like a C shape. The duodenum wraps around the head of the pancreas. The pancreas's tail heads laterally towards the spleen. The stomach is tucked quite neatly under the liver, which looks like a simple triangle from this angle. Looking around the back, its shape, though it has been simplified here, is more complex, allowing passage of the IVC and the aorta through here. It pushes down the right kidney, which is slightly lower than the left. The left kidney sits just underneath and behind the spleen, which is just behind the stomach. If we move around back now to the duodenum, you may hear anatomists split it into four parts. These parts correspond to the angles that it's travelling on. You have part one here, then part two, part three, and then part four. The gallbladder sits just here, anterior to the first part of the duodenum. You may have noticed that there is this space here. Before we go any further on that point, all the organs in the abdomen are covered in this fine membrane called peritoneum. If we opened up somebody's abdomen, they'd actually look a bit more like this. But for simplicity's sake, let's remove all that now. So there's a small sheet of peritoneum hanging between the liver and the stomach, which is called the lesser omentum. And the lesser omentum is that small space from before, which we call the lesser sac. Relevant to the lesser sac, I'm going to mark this part of the liver here and then remove that model. Getting forward now, that if in anatomy class, you can find a hole here between the liver, this part of it, the duodenum, the inferior vena cava, and then the lesser omentum. If you try poking your finger through that hole, that's the omental foramen you're poking your finger through, and your finger will now be inside the lesser sac. So the lesser omentum, as you can see, connects to the lesser curvature of the stomach. And from the greater curvature comes the greater omentum, which folds down and covers the whole abdomen like an apron. Back to the gastrointestinal tract. Now the end of the duodenum becomes the start of the small intestine, which is a six-metre long tube, all wrapped in peritoneum, and attached to the posterior abdominal wall by something called the mesentery. The mesentery is just a sheet of peritoneum with vessels, lymph nodes, and nerves all inside it. The end of the small intestine then plugs into the cecum, which is the first part of the colon or the large intestine. The colon has two flexures, or 90-degree angles here and here, so this is the hepatic flexure, as hepatic means of the liver, just beneath the liver there, and this is the splenic flexure because of its proximity to the spleen. The appendix is located just near the cecum there. And the last part of the large intestine is called the sigmoid colon. Sigmoid means S-shaped, you can see its orientation there. The sigmoid colon is continuous with the rectum, which then ends in the anal canal. And the bladder, lastly, sits underneath the sigmoid colon. Click the link below to have a look around this model yourself, highly recommend you do that. Hit the like button if you enjoyed this video, thank you very much for watching and we'll see you next time.