I. Classification of Malabsorption Syndrome

Malabsorption syndromes are usually caused by defective digestion or absorption in the small intestine but may also be associated with abnormalities of the stomach. In many patients there is malabsorption of fat, causing steatorrhoea and diarrhoea, but malabsorption may involve other substances without affecting fat absorption and for this reason the term “malabsorption syndrome” rather than steatorrhoea is generally used to describe the whole group of conditions. Before discussing the classification of these conditions, a brief account will be given of the physiology of digestion and absorption in the small intestine. After homogenisation and lubrication in the mouth, food is swallowed into the stomach where further homogenisation occurs and where digestion begins. The chyme is then propelled through the pylorus into the small intestine and digestion and absorption are completed. Fig. 1 illustrates diagrammatically the sites at which different substances are absorbed in the small intestine. Substances such as glucose, inorganic iron and probably folic acid, which require no digestion, appear to be absorbed as soon as they reach the absorbing surface of the upper small intestine (Verzár and McDougall, 1936; Hahn, Bale, Ross, Balfour and Whipple, 1943; Cox, Meynell, Cooke and Gaddie, 1958). Fat and protein, however, require preliminary emulsification and digestion by the bile and pancreatic enzymes and they are therefore absorbed more slowly.