Surface infrastructure of the Small Intestine Mucosa in Healthy Children and Adults: A Scanning Electron Microscopic Study with Some Methodological Aspects

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Abstract
Biopsy specimens of light microscopically (LM) normal small intestine mucosa from eight healthy, constitutionally short-statured children without signs of gastrointestinal disease and six healthy adults were studied by scanning electron microscopy (SEM) supplemented by transmission electron microscopy (TEM). The effects on surface morphology of various preparative procedures were also investigated, using small intestine mucosa from cats and rats. Fixation with OsO4–either alone, or following glutaraldehyde fixation–markedly changed the surface ultrastructure compared to that after glutaraldehyde fixation only. By low power SEM, some differences were observed in the appearance of the small gut mucosa between adults and young children. In adults and in children above 3 years of age, the villi were usually shaped like fingers or leaves, but in infants, ridge-shaped villi predominated. The villi showed, however, a smooth surface in both infants and adults, and medium and high power SEM displayed similar pictures, irrespective of age; here the typical structural features of the normal small gut mucosa in humans were (1) distinct extrusion zones at the crests of the villi and almost no signs of enterocyte extrusion along the sides of the villi, and (2) regular enterocytes with polygonal, flat, apical surfaces covered by a thick gly-cocalyx that obscured the underlying microvilli.