Malfunctions of the organs of digestion from the esophagus to the rectum. The gastrointestinal tract usually functions unnoticed, intruding into consciousness only in the form of specific sensations of hunger, intestinal motion, or the need to defecate. However, it is subject to a wide array of pathologic states.
Esophagus
The esophagus is the site of two principal disorders: disturbance of the muscular contractions, and mechanical interference with the passage of food caused by a narrowed lumen. Carcinoma of the esophagus produces mechanical obstructions to swallowing; the long-term prognosis is poor. Excessive acid reflux or regurgitation from the stomach may result in inflammation of the lower esophagus with heartburn and indigestion. Changes in diet and eating habits may bring relief.
The prime example of muscular or neuromuscular disorder is achalasia, a condition of unknown etiology characterized by degeneration of the nervous mechanisms that coordinate contractions of the esophagus and relaxation of the lower esophageal sphincter. Swallowing solids and liquids is difficult, and nutritional consequences usually result.
Other disorders that affect the esophagus include connective tissue diseases such as scleroderma or dermatomyositis. Scleroderma is characterized by weakening of the smooth musculature, which is present in the lower two-thirds of the esophagus, and the lower esophageal sphincter. Dermatomyositis affects the striated musculature present in the upper third of the esophagus. See also Connective tissue disease.
Mechanical problems include stricture or scarring of the lower esophagus, which usually develops from acid reflux. Swallowing is also impeded mechanically by a lower esophageal, or Schatzki, ring, which is a mucosal constriction at the junction of the esophagus and stomach in the presence of a hiatus hernia. See also Hernia.
Carcinoma of the esophagus causes mechanical obstructions to swallowing.
Reflux esophagitis is an inflammation of the lower esophagus that results from excessive acid reflux or regurgitation from the stomach.
Stomach
The stomach is the site of secretion of the highly concentrated hydrochloric acid. The lining of the stomach and duodenal both need to be protected against the effects of the acid.
Peptic ulcer disease is characterized by breaks in the mucosa of the proximal duodenum (duodenal ulcer) or stomach (gastric ulcer). Duodenal ulcer is one of the most common maladies, but for unknown reasons its incidence seems to be declining. It is associated with high concentrations of hydrochloric acid caused by excessive gastrin secretion. In persons with a gastric ulcer, acid concentrations are usually normal or low. The cause of gastric ulcer is not known but may involve increased reflux of bile and other constituents of the small intestine.
Inflammation of the stomach lining, known as gastritis, ranges in severity from acute to chronic and can ultimately lead to atrophy of the tissues and loss of function.
The typical symptoms of gastric cancer include early satiety after eating small amounts of food, abdominal pain, anemia from blood loss, and difficulty in swallowing. Benign stomach tumors are usually asymptomatic but may cause bleeding.
Small intestine
The small intestine is normally resistant to disease. When nutrition is adequate, structure and function remain intact into old age with only slight changes if no specific diseases occur. A prototypical disease of malabsorption is gluten enteropathy, or nontropical sprue. Probably due in part to genetic abnormalities, gluten enteropathy is characterized by inflammation and loss of the normal architecture of the small intestine following ingestion of some proteins. The causative substance is contained in gluten, the protein of cereal grains; a gluten fraction, gliadin, contains the toxin that is responsible. A gluten-free diet, once it has been adopted, is usually maintained for life. Other conditions may also interfere with the absorptive function of the small intestine. Tropical sprue, found in tropical and subtropical climates, resembles gluten enteropathy in its manifestations. It may, however, be an infectious diarrhea; it can be treated with antibiotics and high doses of folic acid. A gluten-free diet does not cure the condition. Infections within the small intestine, particularly those of the parasite Giardia lamblia, may also cause malabsorption. Bacterial infection by Escherichia coli causes most cases of traveler's diarrhea. Among the many other diseases that may lead to malabsorption is regional enteritis, or Crohn's disease. See also Inflammatory bowel disease.
Of all the body's organs, the small intestine is one of the most resistant to neoplastic disease. Benign tumors are rare, as are cancer and lymphoma. (In some familial conditions, however, benign polyps may develop.)
Colon
The colon, or large intestine, is subject to malfunction of widely varying degrees, ranging from mild irritation to life-threatening diseases.
Disturbance of bowel function is among the most common complaints. Constipation probably predominates, particularly with advancing age, but loose stool and diarrhea are also frequent and troublesome. A familiar condition associated with altered function is irritable bowel syndrome, a nonspecific label for an intestinal disturbance without known anatomic cause. See also Diarrhea.
In diverticulosis, small pouches appear along the wall of the colon. Diverticulosis is associated with high pressures within the colon and particularly its narrowest segment, the sigmoid colon. The pressure pushes the mucosa through the weakest points in the wall, leading to formation of the diverticuli.
The second most common internal cancer is that of the colon and rectum. Cancers frequently arise in benign polyps of the colon, which are stalklike or leafed structures (villous adenomas). A high intake of red meat and low fiber and low vitamin A consumption may be contributing factors; a genetic predisposition has been suggested.
Hemorrhoids are veins near the anus that have become distended or occluded. The cause is not fully understood but may be related to straining at stool.
Appendix
Appendicitis, that is, inflammation of the vermiform appendix, was once common among young people but is now relatively rare; the reason for the sharp drop in frequency is unclear. Appendicitis seems to result when a hardened piece of fecal matter known as a fecalith becomes trapped within the appendix and causes infection that can lead to gangrene. If the condition persists, the appendix may perforate, resulting in widespread infection in the abdomen. See also Appendicitis; Cancer (medicine); Digestive system; Tumor.
