Spatial Distribution of Intestinal Activities **

As a first approximation, the small intestine can be viewed as a cylinder, and we can inquire about the distribution of intestinal activities as a function of length, depth within the wall, and angular direction from the mesentery (Fig. 1). Studies of intestinal distributions, still in their early stages, have already proven useful in a number of situations: FIG. 1. Schematic diagram of the small intestine. 1.) They permit a correlation between the spatial distribution of cell types and the occurrence of biochemical activities (for example, serotonin distribution down the small intestine was shown to correlate with the prevalence of argentaffin cells in each section).' 2.) Distribution studies have permitted recognition that all parts of the small intestine do not evolve at the same rate, and that the final (adult) pattern may be arrived at by different pathways.2 3.) They allow quantitative distribution patterns to be contrasted in health and disease, and the kinetic characteristics of enzyme or transport systems to be compared in various sections of the intestine. 4.) These studies permit a correlation of activities, both spatially and temporally. This combination may prove of value in elucidating the interrelationship of U7 intestinal events. I A 5.) Distribution studies have allowed an R f. initial approach to the correlation of enzyme activities and transport events.3 By the use *>< ' of techniques which are often followed by enzyme induction, they permit an assessment of the effect of enzyme changes on a i transport. a Presented here is a summary of data on the distribution of small intestinal activities, R is the radius of the gut wall; and a discussion of the implications and A is the angle from the mesen-uses of such information. It should be tery; a represents the arterioles pointed out that distinct spatial distribu-of Length L. tions of activity are not unique to the small FIGb 2. Representation of the intestine. For example, acetylcholinesterase has been found to be distributed linearly along peripheral nerves, with highest activity near the cell body.' ANGULAR DISTRIBUTION Vessels arrive at the intestine via the mesentery, thus creating a distinction between mesenteric and antimesenteric borders. In most cases, the arriving artery is split into two branches which encircle the gut and send offshoots into the wall. The simplest situation is schematized in Figure 2. Arterial pressure is greatest at the mesenteric border and least at the anti-mesenteric side. For an intestine …