Salt and water absorption in the human colon: a modern appraisal

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Abstract
The human colon has a nominal mucosal surface area of about 2000 cm2,3 but in reality the total absorptive area is even greater because colonic crypt cells are capable of absorption as well as secretion.4 Although it is well established that the rates of colonic salt (Na+ plus Cl−) and water absorption are directly related,5 it is only recently that we have begun to appreciate the array of Na+absorptive processes present in human colon. These show considerable intrinsic segmental heterogeneity.6-10 This explains, at least in part, why the colon’s capacity for sodium and water absorption in vivo is greater in the proximal (ascending) segment than in the distal (descending and sigmoid colon/rectum) segment.11-15 Several different active (transcellular) Na+ absorptive processes exist in human colon. It will become clear that segmental differences in the distribution and regulation of these processes play an important role in colonic Na+ salvage during periods of salt deprivation, in the presence of mucosal inflammation, and after surgical resection.