Porth's Essentials of Pathophysiology, 4e

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Gastrointestinal and Hepatobiliary Function

U N I T 8

Hiatal Hernia Hiatal hernia is characterized by a protrusion or hernia- tion of the stomach through the esophageal hiatus of the diaphragm. There are two anatomic patterns of hiatal herniation: sliding (axial) and paraesophageal (nonax- ial). 6 The sliding hiatal hernia is characterized by a bell- shaped protrusion of the stomach above the diaphragm (Fig. 29-1A). Small sliding hiatal hernias are common and considered to be of no significance in asymptom- atic people. In paraesophageal hiatal hernias a separate portion of the stomach, usually along the fundus of the stomach, enters the thorax through a widened open- ing (Fig. 29-1B). The hernia progressively enlarges and increases in size. In extreme cases, most of the stomach herniates into the thorax. Large paraesophageal hernias may require surgical treatment. Gastroesophageal Reflux The term reflux refers to backward or return move- ment. In the context of gastroesophageal reflux, it refers to the backward movement of gastric contents into the esophagus, a condition that causes heartburn or pyro- sis. Most people experience heartburn occasionally as a

result of reflux. Such symptoms usually occur soon after eating, are short lived, and seldom cause more serious problems. The lower esophageal sphincter regulates the flow of food from the esophagus into the stomach. Both inter- nal and external mechanisms function in maintaining the antireflux function of the lower esophageal sphinc- ter. The circular muscles of the distal esophagus con- stitute the internal mechanisms, and the portion of the diaphragm that surrounds the esophagus constitutes the external mechanism (Fig. 29-2). The oblique muscles of the stomach, located below the lower esophageal sphincter, form a flap that contributes to the antireflux function of the internal sphincter. Relaxation of the lower esophageal sphincter is a brain stem reflex that is mediated by the vagus nerve in response to a number of afferent stimuli. Transient relaxation with reflux is common after meals. Gastric distention and meals high in fat increase the frequency of relaxation. Normally, refluxed material is returned to the stomach by second- ary peristaltic waves in the esophagus, with swallowed saliva neutralizing and washing away the refluxed acid. Gastroesophageal Reflux Disease The persistent reflux of gastric contents into the esoph- agus is referred to as gastroesophageal reflux disease (GERD). 8–10 It is thought to be associated with a weak or incompetent lower esophageal sphincter that allows reflux to occur, the irritant effects of the refluxate, and decreased clearance of the refluxed acid from the esopha- gus after it has occurred. In most cases, reflux occurs dur- ing transient relaxation of the esophagus. Delayed gastric emptying also may contribute to reflux by increasing gas- tric volume and pressure. Esophageal mucosal injury may occur and is related to the destructive nature of the reflux- ate and the amount of time it is in contact with mucosa. The mucosa is partially protected by mucin and alkaline secretions from the submucosal glands. Injury occurs when the reflux episodes are frequent and prolonged. Agents that decrease the tone of the lower esophageal

Esophagus

Thorax

Stomach

Diaphragm

Abdomen

Body of stomach

A

Esophagitis

Esophageal stricture

Esophagus

Erosive esophagitis

Thorax

Diaphragm

Stomach

Stomach

Diaphragm

Incomplete closure of lower esophageal sphincter

Abdomen

Body of stomach

Acid reflux

FIGURE 29-2. Gastroesophageal junction and site of gastroesophageal reflux. (From Anatomical Chart Company. Atlas of Pathophysiology. Springhouse, PA: Springhouse; 2004:171.)

B

FIGURE 29-1. Hiatal hernia. (A) Sliding hiatal hernia. (B) Paraesophageal hiatal hernia.