Wanderings in the small intestine.

Abstract

T HE small intestine is a fascinating = o r g a n through which to wander. It combines digestive, absorptive, metabolic and endocrine functions. Areas that are morphological ly similar are functfonally quite different for example, bile acids and vitamin B,= are selectively absorbed in the terminal few feet of the ileum, but not from the structurally similar mid-ileum. To review the funcbons of the smal l intestine [s not the purpose of this article, but some concentra6on on aspects of work on the small intestine of particular interest to the group working on disorders of this organ in University Colrege, Galway is attempted. The clinical effects of cys5nuria are due to the formation of renal calculi because of a defective renal tubular reabsorption of cystine. Ornithine, lysine and arginine are also poorly re-absorbed in the renal tubules. Milne et al. (1961) first demonstrated that malabsorption of some of these amino acids was present in cystinurir patients. In 1964 it was possible to demonstrate that the active transport system of these amine acids in the small intestine of two cystinuric patients was absent (McCarthy et al., 1984). Mult iple intestinal biopsies from these patients were incubated with dilute solutions of amino acids and at the end of a period of incubation the level of the amino acids in the intestinal tissue water was no higher than that in the incubation fluid. No histological abnormality was present ~n the cystinuric mucosa Intestinal tissue from non-cystinuric patients concentrated the amino acids six to eight times. Major structural differences do not exist between the proximal and minor differences are apparent and in some instances correlate with functional dissimilarities. The villi of the proximal small intestine of the golden hamster are long and slender compared to the shorter villi of the distal intestine, and the proximal intestine is more effective to the esterification of fat. Comparison of fatty acid esterification by vill i of different shape in the hamster, rat, guinea pig and pigeon also show this correlation of function and structure (McCarthy and Tyor, 1964). Coeliac disease is a common disorder of the small intestine. Described by Gee in 1585, it was not unti l more than 60 years later that Paulley (1954) demonstrated that the malabsorption in the disease is due to gross damage to the mucosa. This description was some years after Dicke's (1950) major breakthrough on the role of gluten in the disease. For the practical management of patients, this disorder may be described as a condition in which the small intestinar rnucosa is significantly abnormal and in which improvement occurs when gluten is excluded from the diet. Difficulties occur when this definition is applied to indNidual patients. A patient with an initial response to a gluten free diet and a return towards normal of the intestinal mucosal morphology wil l certainly be considered as having classical coeliac disease. When such patient is given gluten with resultant deterioration in mucosal morphology, and who then fails to improve again when g~uten is removed from the diet is difficult to classify. Initially classification as a coe[iac is cerdistal parts of the small intestine, but tainly correct but what of later on ? What