Читать книгу Pathy's Principles and Practice of Geriatric Medicine - Группа авторов - Страница 362

Ageing is associated with cell loss in the myenteric plexus of the human oesophagus and a decline in conduction velocity within visceral neurons. The consequent reduction in sensory perception may contribute to reduced food intake by inhibiting the positive stimuli for feeding. Older adults frequently complain of increased fullness and early satiation during a meal. This may also be related to changes in gastrointestinal sensory function; ageing is associated with reduced sensitivity to gastrointestinal tract distension. Reduced sensitivity to the satiating effects of distension might be expected to increase, not decrease, the food intake in older people. However, proximal gastric distension has been found to have similar effects on food intake in healthy older and young adults, and the role of impairment of gastric sensory function in causing anorexia of ageing is unknown. Ageing is probably associated with impaired receptive relaxation of the gastric fundus. As a result, for any given gastric volume, there is more rapid antral filling and distension and earlier satiety. This impaired gastric accommodation response in the elderly may be because of altered fundic nitric oxide (NO) concentrations. Peripheral NO causes receptive and adaptive relaxation of the stomach, leading to dilation of the fundus and, ultimately, slower gastric emptying. The increase in NO with ageing may therefore contribute to the slower gastric emptying observed in the elderly.

Most, but not all, studies indicate that gastric emptying slows slightly but significantly with increasing age. Clarkston et al. found that healthy older subjects were less hungry and more satiated after a meal than young subjects and that postprandial hunger was inversely related to the rate of gastric emptying. The effects of ageing on gastric emptying rate may require ingestion of a relatively large energy content, as small meals have not been shown to have different emptying rates in old compared with young individuals. Delayed gastric emptying in older people may result, in part, from the enhanced release of small intestinal hormones such as CCK (see the following section). In contrast, it seems that age has little, if any, effect on small intestinal or colonic motor function, and orocaecal and whole‐gut transit time are not affected in the healthy elderly. Healthy older people do have slower Phase III migration velocities and more frequent ‘propagated contractions’ in the small intestine, but no differences in duration of postprandial motility or amplitude or frequency of either fasting or postprandial pressure waves.²⁴