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This chapter emphasises the importance of psychological processes in influencing the gastrointestinal tract. Chronic functional gastrointestinal symptoms can be seen as a result of dysregulation of intestinal motor, sensory, and central nervous system (CNS) activity.
A central aspect of functional gastrointestinal disorders is pain, and anxiety is seen as an important modulating factor in pain perception. Perception of somatic stimuli probably differs between patients and in some patients there is an exaggerated experience of pain in response to mildly painful or even normal visceral stimuli. Sensitisation can lead to somatisation, which means the development of somatic complaints which cannot be fully explained by any known medical condition—that is, a patient with somatisation has a tendency to notice many bodily sensations and to interpret them as symptoms of organic disease. It is suggested, therefore, that treatments may target a higher cognitive level (for example, behavioural therapy) as well as the end organ (that is, the gut). Patients with functional disease as well as “psychiatric” patients might benefit from this. The relative efficacy of different treatments depends on the particular aetiology of the condition, although it is probably worth treating the end organ in any case.
As the enteric nervous system (ENS) is central to normal gut function, it is of major importance to clinicians who deal with a variety of manifestations of gastrointestinal disease. The ultimate goal is to relieve symptoms and thereby improve the patient's quality of life. The problem is to understand the physiology of symptoms. Ultimately, it is the ENS which causes the response. For example, in constipation (predominantly a disorder of intestinal motor function), there is a decrease in the frequency of motor events, which results in slowing in the emptying of faeces. Behavioural therapy has transformed the treatment of many patients with constipation, by changing CNS regulation of colonic motility. In irritable bowel syndrome patients with diarrhoea, there is also evidence that the primary disorder is one of central regulation of gut function. Most disorders involve disturbances of motor, sensory, and secretory function, although predominance of one particular dysfunction (for example, motor in constipation) permits more selective targeting with drugs. Loperamide is a good example of a drug which targets primarily secretory and motility dysfunction. The same gut symptom (for example, diarrhoea) may often be targeted at more than one site—for example, the somatostatin analogue octreotide acts on a specific enteric receptor to modify visceral blood flow but it also inhibits gastrointestinal motor and secretory function. This compound has transformed the lives of some patients with short bowel syndrome. Patients with specific syndromes of this type should provide useful models for investigation of drug/receptor mechanisms.
In conclusion, the ENS involves complex interrelationships of processes at both the cognitive level and at the end organ. More research is required to define what is normal in the way of traffic into and out of the ENS. In many disorders there are disturbances at more than one level and it may be necessary to target the disorder at more than just the end organ. By studying specific medical syndromes and testing drugs with known receptor activity, it may be possible to work back towards elucidation of the mechanisms of dysfunction.
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