Colon physiology

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Considering the size of the organ and the number of symptoms which are rightly or wrongly attributed to it, too little attention is given to understanding how the colon functions. Although many studies concerning the anatomy, nervous intervention, electrical properties and transport properties are available, they are often poorly understood by those treating patients with colonic diseases. This paper focuses on the physiologic properties of the normally functioning colon and will touch briefly on some derangements in physiology which accompany some of the commoner diseases affecting the colon.

Structure and function

The length of the colon varies considerably in the normal population. There is a rough correlation between a person's height and the length of the colon. Although accurate estimation of the length in vivo may be difficult, and postmortem studies may similarly distort the actual length, studies indicate that the colon is approximately 1500 cm in length.1 The rectal mucosa is a flat surface lacking villi and is lined by columnar epithelial cells. Invaginations from the flat absorptive surface called crypts occur. Below this lies the muscularis mucosa and the submucosa which lack distinguishing characteristics. The muscle layers are two in number. Surrounding the submucosa is an inner-circular muscular layer, and external to this is a longitudinal muscle layer. Unlike other portions of the tubular gut, the outer muscular layer does not completely surround the tube but, instead, is gathered into three distinct longitudinal bundles called taeniae coli. External to the outer muscular layer is the serosa.

The function . . .



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