THE ROLE OF THE SMALL INTESTINE IN NUTRITION

The title chosen for this article requires some further definition. A rigid delimitation is, however, neither possible nor desirable. The small intestine is the portal by which practically all the nutritive material enters the body. Absorption is its predominant role, digestion and the onward movement of food being preliminary stages of this process. These considerations determine the nature of this review and, while attention is mainly given to the problems of absorption, those of the digestive and motor functions of the intestine will not be disregarded. The subject of absorption may be approached from two aspects. First, there are the fundamental problems concerning the processes that determine the passage of water and soluble digestion products from the intestinal lumen into the circulating body fluids; and secondly, the influences, proximate and remote, of the nature of the food ingested on the functions of the small intestine. Regard must also be paid to other organs and to physiological states of the body as a whole that may have definite influences on the assimilation of food. ABSORPTION. The subject of intestinal absorption has already been reviewed in this journal by Goldschmidt (1). The general impression obtained from his article is that the laws of physics and chemistry, although inadequate to explain all the phenomena connected with absorption, are nevertheless factors of very considerable importance. He expressed the opinion that further study of the subject would very probably demonstrate greater and greater dependence of the absorptive processes on physical laws as then established. Has the position altered appreciably since then? The volume of experimental work done with a direct bearing on the subject has not been as great as its importance deserves; but the evidence that has accumulated has tended to place a greater degree of responsibility on the activity of the epithelial cells of the villi. Thus in 1924, Hijber (2), one of the principal antagonists of the “selective action ” view of absorp-tion, stated that no doubt could exist as to the presence of a specific motive force in the intestinal epithelial cells