Aging and the Gastrointestinal functions
This essay deals mainly with physiological but not extensively the structural changes that take place in the gastrointestinal system with aging. It contains the following sections, you need only to click on the required sub-heading to be taken to the underlying content.
Changes in gastrointestinal motility:
esophageal gatric intestinal colonic anorectal
Changes in gastrointestinal secretory functions
salivary gastric pancreatic biliary
Changes in digestion and absorption
of proteins of carbohydrates of fats
Other changes in the gastrointestinal tract
Aging can be defined as the physical and mental changes that
occur with the passage of time. The physical
changes involve the structure and function of the various systems
making up the body. However, some of the systems have a
large reserve capacity, therefore, no major changes
attributed to aging leading to major medical conditions are found
in them. Moreover, the presence of any underlying disease
or the intake of certain drugs is sometimes the major drive for
the occurrence of some of the changes which may be wrongly
attributed to aging. The gastrointestinal tract is an
example on such phenomena . In the following paragraphs, the
motor, secretory, digestive and absorptive changes taking place
in the gastrointestinal tract due to aging are going to be
Changes in gastrointestinal motility:
Motility in the gastrointestinal tract acts to physically breakdown food, emulsify fat, mix food with digestive juices, maximize the exposure of digested food to absorptive cells and to control the propulsion of food along the digestive tract. Changes in the gastrointestinal motility which are due to aging are found in the esophagus, stomach, small intestine, colon and in the anorectal region.
Changes in esophageal motility:
In the esophagus, aging processes in addition to presence of medical problems such as diabetes mellitus and intake of drugs, lead to various changes that affect the overall function of this organ which are mainly concerned with motility(4) . However, in an otherwise healthy elderly person, the changes are so minor to cause any major disability. Presbyesophagus is the term given to describe an esophagus with esophageal motor dysfunction attributed to aging(1) . A presbyesophagus has decreased contractile amplitude, decreased polyphasic waves in the esophageal body, incomplete sphincter relaxation and esophageal dilation (4) . With age, there appears to be a gradual decrease in the upper esophageal sphincter pressure, but the resting pressure of the lower esophageal sphincter seems not to be significantly affected(3) . In addition, there is a delay in the upper esophageal sphincter relaxation after swallowing which itself, i. e swallowing, needs a higher than usual sensory stimulus in order to be initiated (4) . Furthermore, due to the increased resistance to flow across the upper esophageal sphincter caused by the loss of compliance with age, there is an increase in the pharngeal contraction pressures as well as the pharngeoesophageal wave velocity. Moreover, there is a significant increase in the occurrence of asynchronous contractions with failure of contractions after swallowing in the distal esophagusv (3) . In addition, the secondary esophageal peristalsis, which constitute a major clearence mechanism for refluxed gastric acid, seems to be evoked less frequently and less consistently, this increases the liklyhood of the occurrence of gastroesophageal reflux with age. Moreover, numerous non-repulsive tertiary contractions are seen (4). As a result of the disordered motility of the esophagus, esophageal emptying is delayed (3) . The previous changes in the esophageal motility may be explained by the occurrence of neuromuscular degeneration, in addition to the decreased number of myentric neurons in the esophagus with aging. Moreover, the partial denervation might contribute to the disordered peristalsis (1) . Gastroesophageal reflux and dysphagia are among the diseases commonly seen in elderly people due the malfunctioning esophagus.
Changes in gastric motility:
In the stomach, and with aging, there is a mild delay in
gastric emptying time, and the overall gastric motility seems to
decrease (2) . It is noteworthy that the delayed gastric
emptying affects only the emptying of liquids, while the emptying
of solids is the same as in younger people. However, it is
known that decreased gastric acidity leads to accelerated solids
emptying, and since hypochlorhydria is commonly seen in elderly
people, it is logic to say that gastric emptying of solids is
accelerated, nevertheless, it remains sort of unchanged.
This suggests that the gastric musculature is weakened by aging
processes, thats why solids emptying remains apparently
intact (3) .
Changes in intestinal motility:
The motility of the small intestine remains intact with advanced age and there are no major abnormalities with the intestinal transit time after a meal (5) . Although all phases of the migratory motor complexes are preserved, there are minor changes in the motility index and amplitude of contraction, of which no clinical consequences has been described (3) . Moreover, decreased contraction tone has been postulated but not proven in regard to aging. It is worth mentioning that the presence of any systemic diseases such as diabetes mellitus or the intake of certain drugs such as the tricyclic antidepressants lead to altering the motor function of the small intestine (2) .
Changes in colonic motility:
The motility functions of the colon are also well preserved in an aged person, although various medical problems such as constipation are common amongst elderly people. These problems are usually due to other reasons rather than to disordered colonic motility. Numerous drugs such as anticholinergics and narcotic analgesics are known to affect colonic motility leading to constipation (3) . Moreover, with age, there is an increase in both the longitudinal and circular smooth muscle layers along with an increase in the elastic and connective tissues, leading as well to constipation and fecal impaction (5) . Moreover, there may be a mild delay in the emptying of the cecum and ascending colon along with mildly reduced peristaltic activity resulting from autonomic neuropathies and resulting in constipation (2) . Apart from all that, manometric studies of the colon in the elderly fail to identify any age-related decrease in the motility. In the aged colon, both segmental contractions and massive movements increase after a meal exactly like in young colons, but these types of motility are only associated with propulsive activity in elderly people who are physically active (1) .
Changes in anorectal motility:
The motility of the anorectal region changes with aging.
There is decreased rectal elasticity and the rectal volumes at
which external sphincter tonic activity is lost diminishe,
nevertheless, subjective sensations of rectal volumes are
maintained (1) . Investigation of the anorectal function
using anorectal manometry with emphasis on the internal sphincter
function in relation to resting anal canal pressure,
revealed significant reduction with aging. The same studies
found several aged people with normal anal pressures who are
having incontinence, the majority of whom had major associating
medical conditions such as congnitive impairment, diabetes or
inflammatory bowel disease (3) . Therefore, incontinence
cannot always be attributed to aging changes.
Changes in gastrointestinal secretory functions:
The function of the exocrine secretions the gastrointestinal tract produces is to chemically breakdown food macromolecules into absorbable molecules. The secretions are produced in the mouth by the salivary glands, stomach by chief and parietal cells, pancreas and the liver which produces bile. With aging gastrointestinal functions change.
Changes in salivary secretion:
The salivary secretions are produced by the acinar cells
of the salivary glands which are the acinar cells
reduced in number in elderly people. However, no relation
has been described between aging and the reduction in either the
spontaneous or stimulated secretion of saliva. Due to the
fact that saliva is important for the prevention of mucosal
dryness, the prevention of dental caries, and aid in
tasting and speech, a decrease in salivary production
constitutes an important issue for the aged people. Studies
that have suggested decreased salivary production and function
with age, have been limited by factors such as disease and/or use
of medications. Thus, it is possible that the remaining few
salivary acinar cells in old age are enough and efficient in
their function (1) .
Changes in gastric secretion:
In the stomach, there seems to be an overall decrease in the secretory functions. There is a significant decrease in gastric acid secretion both the basal and the stimulated and in response to fixed doses of exogenous gastrin and hypochlorhydria is the term given to describe low acid production (3) . This may be due to atrophic gastritis which increases in prevalence with age. In atrophic gastritis there is loss of parietal cells (2) . However, in case of intact mucosa, gastric acid secretion remains normal despite advanced age (1) . Moreover, gastric production of pepsinogen is also slightly diminished with age. Furthermore, intrinsic factor production by the stomach is also reduced, however, the amounts produced are fairly enough to facilitate the absorption of vitamin B12, therefore, vitamin B12 deficiency is rarely seen, except when the intake of the vitamin is deficient (5) .
Changes in pancreatic secretion :
The pancreatic secretory functions seem to remain intact with
old age upon initial stimulation with either secretin or
cholecystokinin. However, upon repeated stimulation,
pancreatic secretion drops significantly in older people as
compared with younger people (1) . It is worth mentioning
that as the volume of pancreatic secretion drops with repeated
stimulation, the composition of the secretion drops as well in
regard to the bicarbonate and amylase components of the
secretions (3) . Therefore, it appears that the pancreas
might be able to function well under unstressed conditions, and
that was further proved by studies showing that fat malabsorption
doesnt occur in normal circumestances i. e absence of
disease, in elderly humans up to 91 years of age when the
amount of fat in the diet was around 100 g/d, however, when the
amount of fat was increased, mild steatorrhea was developed in
the elderly group but not in the younger age groups (3) .
Although endocrine secretory function of the pancreas is out of
the scope of this essay, it is worth mentioning that serum
insulin levels increase with age, but the sensitivity to insulin
diminishes with age (1) .
Changes in biliary secretion :
Although not much information is available on how the hepatic biliary secretion is affected by aging processes, it seems that the basic production is well maintained enough to full fill the needs, although the composition of the produced bile is altered. With aging there seems to be an increase in the secretion of cholesterol in the bile (lithogenic bile) and a decrease in the synthesis of bile acids, the outcome of which will be a tendency towards the formation of gallstones (5) . Moreover, the gallbladder kinetics and absorptive capabilities do not change appreciably with aging. However, the gallbladder sensitivity to cholecystokinin decreases with aging in humans, this is compensated by increased secretion of cholecystokinin, with an end result of no significant change in gallbladder emptying (3) .
Changes in digestion and absorption with aging:
In the gastrointestinal tract, digestion acts to transform ingested food from large particles into absorbable molecules, and through absorption, those molecules are transported from the lumen of the intestine into the circulation. With aging, there seems to be minor changes in these two functions which are mainly caused by diminished alimentary secretions as mentioned earlier.
Changes in digestion and absorption of proteins:
Although the digestion and absorption of proteins has not been studied in detail, it seems that due to the fact that with advanced age, there is decreased secretion of acid and pepsinogen, the gastric digestion of proteins ( which constitutes about 10 15 % of total protein digestion) in elderly people is less than in younger age groups. However, as long as the pancreatic secretion of pancreatic proteases is intact under unstressed conditions, the major portion of proteins digestion (40 50 %) will remain intact as well. In this regard, experiments have shown that a diet containing 1 g of protein/kg of body weight , revealed normal fecal nitrogen excretion for both younger and older age groups, but when the amount of protein in the diet was increased, increased fecal nitrogen excretion was noticed only in the older age groups, but not in the younger age groups (3) . Finally, the brush border peptidases seem also to remain intact with older age, and these also contribute largely to the terminal digestion of proteins (polypeptides) Moreover, it seems that the absorption of proteins is also well maintained throughout age.
Changes in digestion and absorption of carbohydrates:
With advanced age, the capacity to digest and absorb carbohydrates is decreased. In a study conducted to understand the effect of aging on carbohydrates digestion and absorption, both older and younger age groups were fed a diet containing ? 200 grams of mixed carbohydrates. When breath-hydrogen tests were performed after ingestion of the diet, about 60% of the elderly age group showed positive test results, while there were no positives amongst the younger age groups (3) . Breath-hydrogen test becomes positive when ingested carbohydrates are exposed to colonic bacteria, either due to maldigestion or malabsorption of the ingested carbohydrates. Wither it is maldigestion or malabsorption that is taking place is uncertain yet. However, it is known that in animals and with older age there is decreased activity of several small intestinal brush border enzymes including lactase, maltase, and sucrase-isomaltase, and it is thought that these findings might be applicable to humans and may explain the earlier findings in older humans (5) . In addition, in older age, it is noticed that urinary excretion of D-xylose is decreased, and that was interpreted as being due to deterioration in the renal function rather than due to malabsorption by the small intestine (3) .
Changes in digestion and absorption of fat:
As was previously mentioned, as long as the pancreas is not
over stimulated, fat digestion seems not to be affected by
advanced age. However, putting the pancreas under stress
will result in diminished secretions and reduced fat digestion.
Moreover, as long as the biliary secretion is maintained enough
to aid in the digestion of fat, fat digestion will remain sort of
intact. Fat absorption seems not be significantly decreased in
elderly people. However, some studies found out an increase
in fat absorption with advanced age (3) .
Other changes taking place in the gastrointestinal tract:
These are mainly morphological, and although they are out of
the scope of this essay, it is nice to mention them for the
purpose of completion. In the mouth, the thresholds for the
recognition and detection of flavors become elevated with age (1)
. Moreover, in the stomach, mucosal atrophy is commonly
seen with aging in addition to reduction in the villus height of
the small intestinal mucosa which results in reduced mucosal
surface area (2) . In the colon, mucosal atrophy is also
seen in addition to cellular infiltration of the lamina propria.
Furthermore, the liver decreases in size and its blood supply is
also reduced. Hepatocyte hypertrophy is seen as a
compensation for the reduction in size (3) . However, liver
function test remain normal although some liver functions
deteriorate with age. In the pancreas, there is metaplasia
of the duct epithelium with an increased diameter of the main
duct and dilated acini and ducts (2) .
The gastrointestinal tract has a large reserve capacity and no major changes attributed to aging are seen in an otherwise healthy elderly person. The changes in motility taking place in the esophagus, stomach, small and large intestine and the anorectal region. In the esophagus, there is disordered motility attributed mainly to underlying disease, and these include decreased amplitude of contraction, decreased number of peristaltic waves occurring after swallowing and increased number of disordered contractions in the body of the esophagus. The motility of the stomach witnesses delayed fluid emptying while the small intestinal and colonic motility remain intact. The anorectal motility is affected leading to incontinence which in most of the cases is due to other medical problems. The secretory functions of the gastrointestinal tract are affected by aging. Salivary production as well as the gastric acid secretion are diminished, while pepsin and intrinsic factor production are slightly decreased. Pancreatic secretion is well preserved under unstressed conditions and the biliary composition is altered. The digestion and absorption of proteins seem to be intact or slightly reduced while carbohydrate digestion or absorption is diminished. Fat digestion and absorption is normal if not elevated. Other changes also take place in the gastrointestinal tract and these are mainly morphological.
1. Russell RM : Changes in gastrointestinal function attributed to aging. American Journal of Clinical Nutrition. 55:1203-1207,1992.
2. B. Mark Evers, et al. Organ physiology of aging. The Surgical Clinics of North America. 74:23-37,1994.
3. David F. Altman. Changes in gastrointestinal, pancreatic,biliary and hepatic function with aging. Gastroenterology Clinics of North America. 19:227-233,1990.
4. Jan Tack and Gaston VanVantrappen. Aging and the alimentary tract. Gut. 41: 421- 424, 1997.
5. Hanbrich Williams S. et al. Bockus Gastroenterology.
5th ed. Philadelphia: W. B. Saunders Company, 1995.