PubMed1984
In contrast to the cardiovascular system, the gastrointestinal tract in old age does not reveal the marked structural and functional deteriorations that might be expected to arise from the body's aging process. Besides preserving an active mass of functional tissue, the intestinal regulatory mechanisms show a precise and functional response to the changing circumstances of aging. With regard to the aging processes, therefore, the relative physiological stability of the gastrointestinal system is very important. A possible cause of the maintenance of its functional capacity may be the processes involved in the cellular aging and rapid turnover of the gastrointestinal epithelium. This part of the gut remains practically unchanged and may continue its growth processes almost up to the point of death. Thus, intestinal functions do not seem to deteriorate even in late age. Kinetic studies indicate that the intestinal response in senescense to secure normal absorption processes occurs through an adaptation of transfer (carrier mediated) mechanisms. Such model studies have suggested that with age the affinity of the intestinal carrier mechanisms for the absorption of glucose and neutral amino acids are diminished. Appropriate changes in absorption occur i.e. in the young a faster rate of absorption is achieved at low luminal concentration than in the old. The amounts and activities of many essential intestinal enzymes have been observed to be reduced with age. This too may lead to a slower rate of absorption. In old age therefore it is the rate of intestinal absorption that undergoes a significant change rather than an overall deterioration in absorptive ability. Our present knowledge indicates that there are at least two important regulatory mechanisms that enable the aged gastrointestinal tract to adapt itself to its altered functional capacity. On the one hand, the response of the intestinal epithelium mediated by the various rapid repair processes for the uptake of substances needed by the organism, and, on the other hand, the existence of the current load in the luminal environment controlling the intestinal metabolism and homeostasis in a normal way during aging. An analysis of the close relationship that exists between structure and function in the gastrointestinal tract during aging, in particular the reasons for the observed alterations of the absorptive surfaces, will undoubtedly be useful in the practical elucidation of such problems as mucosal injuries, resection and malabsorption therapy.