Internal structure of the intestinal villus: morphological and morphometric observations at different levels of the mouse villus.

The internal structure of the mouse jejunal villus was examined from apex to base in transverse serial sections. The villi were arbitrarily divided into apical (1-160 microns), middle (161-320 microns) and basal (321-480 microns) thirds. Histological and ultrastructural morphometry was performed on villous epithelium, stroma, blood vessels and lacteals at the three levels. The cross sectional area and the number of cells/section increased apico-basally in both the villous epithelium and the stroma, but the increase was greater in the latter. The enterocytes in the villous basal third were narrow and had oblong nuclei. The enterocytes gradually became wider and their nuclei attained a more round or oval shape towards the villous apex. The microvilli of these cells also increased in length from the villous base to apex. Although the number of capillaries/section was approximately the same at the three levels examined, it appeared that the apical third was relatively more vascular if the overall apico-basal increase in the villous size was taken into consideration. The villi had a single lacteal, whose cross sectional area generally increased towards the villous base. The results of this study indicate that the internal structure of the intestinal villus is not uniform along its length. Therefore, it is important that when studying normal and abnormal villi, like should be compared with like so as to ensure that the normally occurring variations in the villous morphology are not confused with those induced by disease or experimental processes.