The microvascular structure of the normal colon in rats and humans.

The colonic microcirculation may be expected to have a central role in the absorptive, secretory, and protective functions of the colon. To characterize the microvascular structure of the colon in rats and humans, microvascular casts were prepared and examined by scanning electron microscopy. Quantitative measures of the microvasculature were obtained from histological sections. The overall organization of microvessels was found to be similar in the rat and human colon. Capillaries in the colonic mucosa formed a honeycomb-like network around each of the mucosal glands. This capillary plexus was supplied by arterioles which divide into their capillary branches at the level of the submucosa. Mucosal capillaries drain into venules at the luminal surface of the mucosa. Venules then pass to submucosal veins without receiving further capillary branches. Examination of vascular casts also showed that in both the rat and the human colon, there was an increased density of subluminal capillaries in the cecum and proximal colon compared to that of the rest of the colon. This was supported by quantitative measures which indicated a significantly greater microvascular surface area in the rat cecum (24.1 mm2/mm3) compared to that of the midcolon (19.8 mm2/mm3) (P = 0.04) and the distal colon (19.1 mm2/mm3) (P = 0.03). Similarly in the human colon there was a significantly greater total microvascular volume in the proximal colon (13.4%) compared to that of the distal colon (7.7%) (P < 0.0005) and there was a significantly greater total microvascular surface area in the proximal colon (22.4 mm2/mm3) compared to that of the distal colon (17.5 mm2/mm3)(P=0.032). This study details quantitative vascular data for the colon in rats and humans which has not previously been documented, despite its important role in the absorptive function of the colon and in many disease processes affecting the colon. These data provide the normal values with which pathological conditions of the colon which affect the vasculature can be compared.