The Ageing of the Human Lower Bowel

Older people suffer a greater number of disorders of the gastrointestinal tract, including chronic constipation and faecal incontinence. In this review, we examine the age-related degenerative changes that have been identified in the lower bowel of humans. Firstly, older individuals may experience less abdominal pain and a lower incidence of gut-brain disorders that are defined partly by abdominal pain (e.g., irritable bowel syndrome); the causes are unclear. Secondly, an age-dependent reduction in mucosal barrier functions may follow a decline in intestinal stem cell activity, a reduced density of tight junction proteins linking epithelial cells and a decline in mucus layer thickness. This allows antigenic and toxic material to enter the wall of the colon. Thirdly, degenerative changes within the wall of the colon occur in both the ascending and descending regions, but the ascending colon appears most vulnerable. Here, there is reduced cholinergic neuromuscular function (potentially reducing colonic motility), perhaps because of dysfunctional nerve axon transport, and associated senescence-like activity. These changes lower the 'intestinal reserve', that is the capacity of neuromuscular functions to absorb other 'life events' that affect bowel motility (e.g., changes in lifestyle or eating habits, medications that affect neuromuscular functions and diseases such as diverticulosis) without generating symptoms such as constipation. When combined, symptoms are more likely to develop.