Figure 162

Photomicrograph of the esophagus. This low-magnification photomicrograph shows a H&E-stained section of the esophagus with its characteristically folded wall, giving the lumen an irregular appearance. The mucosa consists of a relatively thick stratified squamous epithelium, a thin layer of lamina propria containing occasional lymphatic nodules, and a muscularis mucosae. Mucous glands are present in the submucosa; their ducts, which empty into the lumen of the esophagus, are not evident in this section. External to the submucosa in this part of the esophagus there is a thick muscularis externa made up of an inner layer of circularly arranged smooth muscle and an outer layer of longitudinally arranged smooth muscle. The adventitia is seen just external to the muscularis externa. x8.

As noted, the esophagus is fixed to adjoining structures throughout most of its length; thus its outer layer is composed of adventitia. After entering the abdominal cavity, the short remainder of the tube is covered by serosa, the visceral peritoneum.

Mucosal and submucosal glands of the esophagus secrete mucus to lubricate and protect the luminal wall

Glands are present in the wall of the esophagus and are of two types. Both secrete mucus, but their locations differ.

• Esophageal glands proper occur in the submucosa. These glands are scattered along the length of the esophagus but are somewhat more concentrated in the upper half. They are small, compound, tubuloalveolar glands (Fig. 16.4). The excretory duct is composed of stratified squamous epithelium and is usually conspicuous when present in a section, because of its dilated appearance.

• Esophageal cardiac glands are named for their similarity to the cardiac glands of the stomach and occur in the lamina propria of the mucosa. They are present in the terminal part of the esophagus and frequently, though not consistently, in the beginning portion of the esophagus.

The mucus produced by the esophageal glands proper is slightly acidic and serves to lubricate the luminal wall. Because the secretion is relatively viscous, transient cysts often occur in the ducts. The esophageal cardiac glands produce a neutral mucus. Those glands near the stomach tend to protect the esophagus from regurgitated gastric contents. Under certain conditions, however, they are not fully effective, and excessive reflux results in pyrosis, a condition more commonly known as heartburn.

The muscle of the esophageal wall is innervated by both autonomic and somatic nervous systems

The striated musculature in the upper part of the esophagus is innervated by somatic motor neurons of the vagus nerve, cranial nerve X (from the nucleus ambiguus). The

muscularis., mucosae >

of the food in the stomach by its gastric secretions produces a pulpy fluid mix called chyme. The chyme then passes into the small intestine for further digestion and absorption.

The stomach is divided histologically into three regions on the basis of the type of gland that each contains

Gross anatomists subdivide the stomach into four regions. The cardia surrounds the esophageal orifice; the fundus lies above the level of a horizontal line drawn through the esophageal (cardiac) orifice; the body lies below this line; and the pyloric part is the funnel-shaped region that leads into the pylorus, the distal, narrow sphinc-teric region between the stomach and duodenum. Histologists also subdivide the stomach, but into only three regions (Fig. 16.5). These subdivisions are based not on location but on the types of glands that occur in the gastric mucosa. The histologic regions are the

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