Porth's Essentials of Pathophysiology, 4e

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Disorders of Gastrointestinal Function

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cancer, suggesting that other factors may be involved. 7 Autoimmune gastritis, like H. pylori infection, increases the risk of gastric cancer, presumably due to chronic inflammation and intestinal metaplasia. Most gastric cancers involve the antrum of the stom- ach, with the lesser curvature being involved more often than the greater curvature. Compared with benign ulcers, which have smooth margins and are concen- trically shaped, gastric cancers tend to be bulky and irregularly shaped and have firm and jagged edges. Unfortunately, stomach cancers often are asymptom- atic until late in their course. Symptoms, when they do occur, usually are vague and include indigestion, anorexia, weight loss, vague epigastric pain, vomiting, and an abdominal mass. Because these symptoms are essentially nonspecific, early detection is often difficult. Diagnosis of gastric cancer is accomplished by a vari- ety of techniques, including barium x-ray studies, endo- scopic studies with biopsy, and cytologic studies (e.g., Papanicolaou smear) of gastric secretions. 24 Cytologic studies can prove particularly useful as routine screen- ing tests for persons with atrophic gastritis or gastric polyps. Endoscopy and computed tomography (CT) scans often are used to delineate the spread of a diag- nosed stomach cancer. Depending on the location and extent of the lesion, surgery in the form of radical subtotal gastrectomy usu- ally is the treatment of choice. Irradiation and chemo- therapy have not proven particularly useful as primary treatment modalities in stomach cancer. These methods usually are used for palliative purposes or to control metastatic spread of the disease. ■■ The integrity of the mucosal layer of the stomach is maintained by tight intercellular junctions and the presence of a protective mucous layer. Prostaglandins serve as chemical messengers that protect the stomach lining by improving blood flow, increasing bicarbonate secretion, and enhancing mucus production. Major causes of gastric irritation and ulcer formation are aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs), which exert their destructive effects by irritating the stomach and inhibiting prostaglandin synthesis and Helicobacter pylori infection, which disrupts the mucosal barrier that protects the stomach from the harmful effects of its digestive enzymes. ■■ Gastritis refers to inflammation of the gastric mucosa. Acute gastritis is a transient inflammation of the gastric mucosa, most commonly caused by local irritants such as bacterial endotoxins, caffeine, alcohol, and aspirin. Chronic gastritis, which is characterized by the presence of chronic inflammatory changes leading eventually to SUMMARY CONCEPTS

Disorders of the Small and Large Intestines There are many similarities in conditions that disrupt the integrity and function of the small and large intestines. The walls of the small and large intestines consist of four layers: (1) an inner mucosal layer that lines the lumen of the intestine; (2) a submucosal layer that lies beneath the mucosal layer; (3) the muscularis externa, which has an inner circular layer and an outer longitudinal layer of smooth muscle; and (4) an outer serosal layer or visceral peritoneum that consists of a single layer of flat serous fluid–producing cells (see Chapter 28, Fig. 28-3). The visceral peritoneum is continuous with the parietal peri- toneum, which lines the abdominopelvic cavity. Among the conditions that cause altered intestinal function are irritable bowel syndrome, inflammatory bowel disease, infectious enterocolitis, diverticulosis, appendicitis, dis- orders of bowel motility (i.e., diarrhea, constipation, and bowel obstruction), peritonitis, disorders of intes- tinal absorption, and cancer of the colon and rectum. Irritable Bowel Syndrome The term irritable bowel syndrome (IBS) is used to describe a functional gastrointestinal disorder charac- terized by a variable combination of chronic and recur- rent intestinal symptoms not explained by structural or biochemical abnormalities. 25,26 Prevalence estimates for IBS in North America range from 5% to 10%, with peak prevalence from 20 to 29 years of age. 26 atrophy of the glandular epithelium of the stomach, can be caused by H. pylori (H. pylori gastritis), autoantibodies (autoimmune gastritis), or chronic injury from reflux of alkaline duodenal contents, pancreatic secretions, and bile into the stomach (chemical gastropathy). ■■ Peptic ulcer disease occurs in areas of the upper gastrointestinal tract that are exposed to acid–pepsin secretions, most commonly the duodenum and stomach.The most common complications of peptic ulcers are hemorrhage, perforation, and gastric outlet obstruction. ■■ Cancer of the stomach, while having decreased in incidence in the United States, continues to be a leading cause of cancer deaths worldwide. Among the factors thought to predispose to stomach cancer are carcinogenic factors in the diet (e.g., N-nitroso compounds and benzo[ α ] pyrene found in smoked and preserved food) and chronic gastritis. Because there are few early symptoms with this form of cancer, the disease often is far advanced at the time of diagnosis.