Bottom: diagram showing small intestine, colon, rectum
In the previous article we reviewed how aging affects the oral cavity, esophagus, stomach and small intestine. We will now turn our attention to the effects of aging on the colon (large intestine), rectum, liver, pancreas and gallbladder.
Digested food, now mostly liquid, moves into the colon after passing through the small intestine. Here, most of the water is absorbed back into the bloodstream through the intestinal wall. Bacteria residing in the colon break down remaining nutrients such as certain carbohydrates. The remaining waste material then moves into the rectum until the anal sphincter muscle pushes it out of the body as stool.
In many older individuals, food moves more slowly through the colon and chronic constipation is common. This is more likely to be a result of medication side effects and immobility than aging itself.1 Because food transits more slowly through the colon, more water is absorbed back into the bloodstream. This produces harder stool which also contributes to constipation.
On colonoscopy, many seniors are found to have diverticula lining the inside of their colon. These are outpouchings of the inner wall of the colon that occur due to weakening of the bowel wall and increased pressure that is generated inside the abdomen to move stool out of the body. These diverticula often are asymptomatic but they can become infected or cause bleeding.
Normally, the mucosal wall of the large intestine acts as a barrier to prevent undesirable molecules from entering the bloodstream. With age, this barrier becomes less effective. Thus, older individuals typically have increased levels of pro inflammatory molecules such as bacteria, toxins and antigens moving into the bloodstream from the gut. The intestinal mucosal barrier dysfunction described here is implicated in several conditions including diabetes, metabolic syndrome, fatty liver disease, irritable bowel syndrome, microbial infections, and also in the chronic low level inflammation related to aging known as “inflammaging”.
By the time the partially digested food has moved through the colon, the nutrients and water have been absorbed, leaving stool as a waste product. The external anal sphincter, a mass of muscle 10 cm in length, holds the stool in the rectum until you want to go. Both sexes are affected by decreased resting pressure in the anal sphincter with age. This means that the muscle is less able to generate enough pressure to prevent the stool from leaking out. Fecal incontinence, or leakage of stool, is more common in women. Older females are more likely to suffer from complications of the vaginal birthing process, including pudendal nerve injury and stretching of the pelvic muscles. Nerve and muscle injury is even more likely to occur when episiotomy is performed or when forceps are used to assist in vaginal delivery.
Aging has significant effects on the liver, which is responsible for filtering blood coming from the digestive tract before delivering it to the rest of the body. The liver also processes drugs and removes harmful chemicals from the bloodstream. It secretes a chemical called bile which helps the small intestine digest fat.
Liver mass decreases by 20 to 40% with age while blood flow to the liver drops by up to 50% between age 20 and age 90.2 In elders, the decreased blood flow means that the liver is less able to clear drugs from the body. In fact, metabolic clearance of drugs is 20 to 40% slower in older individuals3 and they often require a lower dose of medication compared with younger patients. The liver is less able to regenerate new tissue after injury. With age there is an accumulation of fat cells and waste products in the liver tissue. This fat accumulation often leads to fatty liver disease, the most common liver disorder worldwide.
The gallbladder, a pear- shaped organ just below the liver, stores and concentrates bile. Its function is mostly preserved with age. However, older people have a higher concentration of cholesterol in their bile, meaning that cholesterol gallstones are more likely to form. Gallbladder disease, most often stone related, is the most common reason for surgery in patients with acute abdominal pain over age 55.4. Acute cholecystitis or infection of the gallbladder becomes much more common with age.
Finally, the pancreas supports the digestion of food by secreting enzymes that assist in this process. There are only minor changes in the digestive functions of the pancreas with aging. As seen in other organs, fat cell infiltration increases with age.
Overall the digestive tract is less affected by age than other organ systems. Acute abdominal pain is often muted in older people, making it more difficult to recognize severe disease when present. Irritable bowel syndrome, a common cause of abdominal pain in younger people, rarely presents in old age. Thus, it should be a diagnosis of exclusion in the older person with new abdominal complaints. Some symptoms, such as constipation, are often related to other factors such as medication side effects or decreased mobility rather than to aging itself.
References
- Fillit, H., Rockwood, K., & Young, J. B. (2016). Brocklehurst’s Textbook of Geriatric Medicine and Gerontology. Berlin: Elsevier.
- McLean AJ. “Aging Biology and the geriatric clinical pharmacology.” Pharmacol Rev 2004; 56(2): 163.
- Turnheim K. “When drug therapy gets old: pharmacokinetics and pharmacodynamics in the elderly.” Exp Gerontol. 2003 Aug;38(8):843-53.
- Lyon C. “Diagnosis of acute abdominal pain in older patients.” Am Fam Physician 2006; 74: 1537-1544.