Physiological Mechanisms

Abstract

The physiology of colonic function is less well understood than in other regions of the gastrointestinal tract. This is largely due to the relative inaccessibility of the colon in vivo, and the lack of a suitable animal model of the human colon. Colonic movements exhibit special features to serve a specific function. Firstly, the movements are organized to produce very slow flow which facilitates the extraction of water and electrolytes from the faecal mass. Secondly, the slow nature of colonic movements facilitates the growth of colonic microflora. In contrast, the contractions of the distal colon are designed to assist defaecation. It is now becoming increasingly clear that, although anatomically the colon is a single organ, in physiological terms the colon consists of three separate regions (right colon, left colon and the anorectum) which require precise coordination to produce normal function. Antiperistaltic contractions are predominant in the proximal colon, whereas slowly moving ring contractions directed aborally are more common in the distal colon.