(3.29)

We'll move on now, to begin our trip along the continuous tube that forms the gastro-intestinal tract. We'll start where the esophagus joins the stomach, and we'll end at the exit, the anal canal.

The stomach is up here: this is just part of it. To get a clear look at the stomach, we'll remove several structures in front of it and below it, starting with this bulky fold of peritoneum, the dependent part of the greater omentum.

Next we'll remove these numerous loops of jejuno-ileum, that make up the greater part of the small intestine. We'll remove them by dividing the double sheet of peritoneum that attaches them to the posterior abdominal wall, the mesentery.

After removing the jejuno-ileum, we'll also remove the colon, which starts down here, and goes up, across and down.

Along with the colon we'll remove this double sheet of peritoneum that goes from the stomach to the transverse colon, the gastro-colic ligament.

With these structures of the way we start to get a much clearer view. The last structure hiding the stomach is the liver. We'll remove this left lobe of the liver.

Now we can see the stomach clearly. All this is the stomach. This is the underside of the diaphragm. Here's the esophagus, coming through its hiatus in the diaphragm. In this view we're looking up at the stomach from about this angle. Much of the stomach lies above the level the costal margin, which is here.

To get a more complete view of the stomach we'll look at it in isolation. Here's the way in: the esophago-gastric junction. Here's the way out: the pylorus, which leads to the first part of the small intestine, the duodenum. The narrow part of the stomach leading to the pylorus is the pyloric antrum. In this specimen it's unusually narrow.

This broad curve, facing to the left, is the greater curve of the stomach. This much tighter curve, facing to the right, is the lesser curve. This upward and backward bulge is the fundus of the stomach: it sits right below the diaphragm.

Here's the inside of the stomach. Like all the parts of the gastro-intestinal tract, its wall is formed by an outer layer of smooth muscle, and an inner layer of mucosa. In the fundus the mucosal layer is smooth; in the pyloric antrum it's thrown into prominent longitudinal folds.

At the esophago-gastric junction the muscle coat of the esophagus forms a partly effective sphincter that keeps the contents of the stomach from passing upwards.

At the pylorus the thickened muscular coat forms a highly effective sphincter that relaxes intermittently to let the contents of the stomach into the duodenum a little at a time. Here are the mucosal folds of the pylorus, protruding into the duodenum.