GASTROINTESTINAL FUNCTION

The gastrointestinal tract shows less age-associated change in function than many other organ systems. Although tooth loss is common, and approximately 40% to 50% of the older adult population is edentulous, it is not consid­ered part of the normal aging process. Poor dental hygiene with associated caries and periodontal disease is the main reason for the loss. Edentia, or toothlessness, can lead to di­etary changes and can be associated with malnutrition. Use of dentures can enhance mastication; however, taste sensation is inhibited. Because of improved dental tech­nology and the fluoridated water supply, more persons are able to keep their teeth into their later years. Xerostomia, or dry mouth, also is common, but it is not universal among older adults and typically occurs as a result of de­creased salivary secretions. Other causes of dry mouth can include medications, such as anticholinergics and tran-quilizers, radiation therapy, and obstructive nasal diseases that induce mouth breathing.

Soergel and colleagues (1964) coined the term pres-byesophagus to denote changes in esophageal function, such as decreased motility and inadequate relaxation of the lower esophageal sphincter, that occur with aging.³³ However, in studies that controlled for disease states such as diabetes mellitus and neuropathies, no increase in ab­normal motility was observed. In general, the physiologic function of the esophagus appears to remain intact with advancing age.

Atrophy of the gastric mucosa and a decrease in gas­tric secretions can occur in older adults. Achlorhydria (i.e., decrease in hydrochloric acid secretion) occurs, prob­ably as a result of a loss of parietal cells. Although not uni­versal, achlorhydria is more prevalent among older adults and can cause impaired gastric absorption of substances requiring an acid environment.

Atrophic gastritis and decreased secretion of intrinsic factor are more common with aging and result in a mal-absorption of vitamin B₁₂. Because vitamin B₁₂ is necessary for the maturation of red blood cells, a deficiency can lead to a type of macrocytic anemia called pernicious anemia. Vitamin B₁₂ deficiency also can cause neurologic abnor­malities such as peripheral neuropathy, ataxia, and even dementia. Treatment consists of regular periodic vitamin B₁₂ replacement therapy through injection because the oral form is not absorbed owing to a lack of intrinsic factor.³⁴

The small intestine shows some age-related morpho­logic changes, such as mucosal atrophy; however, absorp­tion of most nutrients and other functions appear to remain intact. Absorption of calcium, however, decreases with aging and may reflect decreased intestinal absorption along with other factors, such as reduced intake of vitamin D, de­creased formation of vitamin D₃ by the skin because of re­duced sun exposure, and decreased activation of vitamin D₃ by the liver and kidney.

Diverticula of the colon are common among older adults, with more than 50% of individuals older than 80 years having diverticular disease. The high incidence ap­pears to result mainly from a low-fiber diet. Constipation, or infrequent passage of hard stool, is another frequently occurring phenomenon. It often is attributed to immo­bility and decreased physical activity, a low-fiber diet, de­creased fluid intake, and medications; malignancies and other disease states also can be responsible. Complica­tions of constipation can include fecal impaction or ob­struction, megacolon, rectal prolapse, hemorrhoids, and laxative abuse.