Arteriolar, capillary, and shunt flow gradients along the intestine in relation to the weight distribution of the mucosa, submucosa, and muscularis--a microsphere study.

The objective of this study was to establish the basal arteriolar (ART), capillary (CAP), and shunt (SH) flow of the three anatomical layers of the gut wall (mucosa, submucosa, and muscularis) along the intestinal tract of the dog employing a microsphere technique. We also examined whether a gradient of blood flow (BF) exists along the intestine, and if so, how this is related to the blood flow and weight distribution of the three anatomical layers along the intestine. We found the following. (i) In all locations of the intestine a higher proportion of the ART inflow passed through the capillaries of the layers with higher metabolic need, i.e., mucosa (68-79%) and the muscularis (50-79%), than through the capillaries of the submucosa (34-46%). Thus, the distribution between CAP and SH flow in the three anatomic layers of the gut wall, as measured by the microsphere technique, appears to correspond to the functional requirements of these tissue layers. (ii) From the duodenum to the ascending colon (but not along the colon), there was a significant decreasing gradient of ART flow (R2 = 50.6%) and a small and barely significant gradient of CAP (R2 = 11.6%) and SH flow (R2 = 9.7%) of the whole gut wall. (iii) All these gradients were present in the mucosa, but their slopes were higher than those in the whole gut wall; the R2 for the mucosal ART, CAP, and the SH flow was 60.5, 52.7, and 21.6%, respectively. (iv) The ART, CAP, or the SH flow of the submucosa and the muscularis showed no such decreasing gradient. Thus, the gradient of blood flow of the whole gut wall appears to be a reflection of a more prominent gradient of ART and CAP flow of the mucosa. (v) Similar to the mucosal blood flow, the weight distribution of the mucosa showed a craniocaudal gradient (R2 = 69.3%). The latter was found to be directly related to the mucosal blood flow of all locations from the duodenum to the ascending colon, except for the duodenum, which had a higher ART and SH flow than those of several, but not all, distal locations. This higher blood flow of the duodenum could be due to a functional difference of this location.