Chapter 9

The foregut consists of the distal end of the esophagus, the stomach, and a portion of the duodenum. In addition, the pancreas, liver, and gallbladder form embryologically from the foregut and thus also are included in this discussion. The celiac trunk is the principal (but not exclusive) artery supplying the foregut. The celiac trunk arises from the abdominal aorta.

### Esophagus

The distal end of the esophagus enters the abdominal cavity in the upper left quadrant by traversing the diaphragm at the T10 vertebral level. The esophagus immediately transitions into the stomach, with the cardiac sphincter serving as the transition boundary. Coursing parallel to the esophagus are the anterior and posterior vagal trunks. The vagal trunks consist of visceral motor and sensory parasympathetic fibers from the left and right vagus nerves, respectively.

A function of the stomach is the production of hydrochloric acid. If the cardiac sphincter fails to contain the acidic chyme produced by the stomach, the acid moves into the esophagus, irritating its mucosal lining and causing gastro-esophageal reflux disease (GERD). The irritation presents as an uncomfortable, perhaps burning sensation in the region of the esophagus, deep to the heart. As a result, this condition is also referred to as “heart burn.”

### Stomach

The stomach is a dilated, J-shaped portion of the foregut, juxtaposed between the esophagus and the duodenum (Figure 9-1A and B). The stomach is located in the upper left quadrant of the abdomen, with the spleen, pancreas, and aorta located deep to the stomach body.

###### Figure 9-1

A. Parts of the stomach and duodenum. B. Anterior view of the foregut; the lesser omentum is partially removed.

Gastric secretions are churned in the stomach, with food, into a semifluid mixture (chyme) that is eventually transported from the stomach into the duodenum.

The stomach is partitioned into the following four regions:

• Cardia. Surrounds the gastroesophageal opening.
• Fundus. Dome-shaped region superior to the cardia.
• Body. Largest region of the stomach that consists of a lesser curvature and a greater curvature, where the lesser omentum and greater omentum attach, respectively.
• Pylorus. Distal end of the stomach containing the pyloric sphincter, which is located in the transpyloric plane at the L1 vertebral level.

The distal end of the esophagus and gastric fundus can herniate through the esophageal hiatus of the diaphragm into the thoracic cavity. This is known as a hiatal hernia and results from conditions such as strain on the diaphragm due to childbirth or to congenital defects in the diaphragm.

When food enters the stomach, it begins to expand and stretch, resulting in a vagovagal reflex. Visceral sensory neurons from the vagus nerve ...

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