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Figure

Steps in the swallowing reflex. (a) The tongue forces food into the pharynx. (b) The soft palate, hyoid bone, and larynx are raised, the tongue is pressed against the palate, the epiglottis closes, and the inferior constrictor muscles relax so that the esophagus opens. (c) Superior constrictor muscles contract and force food into the esophagus. (d) Peristaltic waves move food through the esophagus to the stomach.

Esophagus

Diaphragm

Esophageal hiatus

Stomach

Esophagus

Diaphragm

Esophageal hiatus

Stomach

The esophagus functions as a passageway between the pharynx and the stomach.

opening, the esophageal hiatus, and is continuous with the stomach on the abdominal side of the diaphragm (figs. 17.15, 17.16 and reference plates 57, 73).

Mucous glands are scattered throughout the sub-mucosa of the esophagus. Their secretions moisten and lubricate the inner lining of the tube.

Lumen

Mucosa

Submucosa

Muscular layer

Figure 17.16

This cross section of the esophagus shows its muscular wall (10x).

Lumen

Mucosa

Submucosa

Muscular layer

Figure 17.16

This cross section of the esophagus shows its muscular wall (10x).

In a hiatal hernia, a portion of the stomach protrudes through a weakened area of the diaphragm, through the esophageal hiatus and into the thorax. As a result of a hiatal hernia, regurgitation (reflux) of gastric juice into the esophagus may inflame the esophageal mucosa, causing heartburn, difficulty in swallowing, or ulceration and blood loss. In response to the destructive action of gastric juice, columnar epithelium may replace the squamous epithelium that normally lines the esophagus (see chapter 5, page 145). This condition, called Barrett's esophagus, increases the risk of developing esophageal cancer.

gion, which balloons superior to the cardiac portion, is a temporary storage area and sometimes fills with swallowed air. This produces a gastric air bubble, which may be used as a landmark on a radiograph of the abdomen. The dilated body region, which is the main part of the stomach, is located between the fundic and pyloric portions. The pyloric region (antrum) is a funnel-shaped portion that narrows and becomes the pyloric canal as it approaches the small intestine.

At the end of the pyloric canal, the circular layer of fibers in its muscular wall thickens, forming a powerful muscle, the pyloric sphincter. This muscle is a valve that controls gastric emptying.

Just superior to the point where the esophagus joins the stomach, some of the circular muscle fibers have increased sympathetic muscle tone, forming the lower esophageal sphincter (lo'er e-sof"ah-je'al sfingk'ter) or cardiac sphincter (fig. 17.17). These fibers usually remain contracted, and they close the entrance to the stomach. In this way, they help prevent regurgitation of the stomach contents into the esophagus. When peristaltic waves reach the stomach, the muscle fibers that guard its entrance relax briefly to allow the swallowed food to enter.

H Describe the regions of the pharynx.

^9 List the major events that occur during swallowing.

^9 What is the function of the esophagus?

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