The aging process has clinically significant effects on oropharyngeal and upper esophageal motility, colonic function, gastrointestinal (GI) immunity, and GI drug metabolism (Figure 89-1). On the other hand, because the GI tract exhibits considerable reserve capacity, many essential aspects of GI function, such as intestinal secretion, are preserved with aging. Despite such adaptation, superimposed effects of chronic diseases and environmental/lifestyle exposures (medications, alcohol, tobacco) can further impair GI function in older patients. A modest decline in gastric mucosal cytoprotection or esophageal acid clearance may become significant when superimposed side effects of certain medications or concurrent disease are also present. Certain age-related changes in GI function, such as constipation, are viewed as dysfunctional by patients and health care providers. Research areas that have been identified as important in aging include the pathophysiology of swallowing disorders, esophageal reflux, dysmotility syndromes, GI immunobiology, and the cellular mechanisms of neoplasia in the GI tract. Animal studies provide important insights into the cellular physiology of aging, despite the issue of species variation.
Effects of physiological aging on the gastrointestinal tract. This schematic diagram summarizes significant effects of aging on various divisions of the gastrointestinal tract. Key: up arrow, increased, down arrow, decreased. (Revised from Hall and Wiley. Age-associated changes in gastrointestinal function. In: Hazzard et al., eds. Principles of Geriatric Medicine and Gerontology, 5th ed. New York, New York: McGraw-Hill; 2003 [chapter 63].)
The increasing likelihood of dental decay and tooth loss with aging affects the efficiency and completeness of mastication (also see Chapter 42). Chewing and swallowing are impaired by xerostomia, which affects roughly 25% of older patients, while as many as 50% have subjective complaints of dry mouth. Medication side effects are a common cause of xerostomia, while a minority is caused by specific diseases affecting the salivary glands, such as Sjogren's syndrome. A mild loss of saliva production appears to occur with normal aging.
After food is broken up in the mouth by mastication, the act of swallowing moves the food bolus from the oral cavity into the pharynx and esophagus (also see Chapter 41). The oral and pharyngeal stages of swallowing are regulated by cortical input to medullary swallowing centers, which innervate skeletal muscle groups in the pharynx. The proximal esophagus contains skeletal muscle controlled by nerves from the medullary swallowing centers, whereas the mid- and distal esophagus consists of smooth muscle regulated by intrinsic enteric innervation and extrinsic innervation by the vagus nerve.
Oropharyngeal swallowing disorders are most commonly observed in patients with cognitive and/or perceptual dysfunction secondary to stroke or dementia, or chronic neurodegenerative diseases that affect the brainstem or motor neurons, such as Parkinson's disease, myasthenia gravis, or amyotrophic lateral sclerosis. Normal aging, however, is associated with alterations that predispose older individuals to dysphagia. Video fluoroscopy demonstrates abnormal transfer of a food ...