A fractographic study combined with light and transmission electron microscopy and3H-thymidine autoradiography was carried out to examine cell proliferation and differentiation of the fundic mucosa. The following results were obtained.1.A gastric gland and a gastric pit into which the gland opens constitute an inseparable structural unit. This unit is called glandular tubule. The glandular tubule consists of an upper, smoothtubular portionand a lower, knobby gastric gland. The tubular portion corresponds to the gastric pit viewed from outside. The so-called isthmus of the gland in which generative cells are confined corresponds to the part of the tubular portion immediately above the constriction.2.Each glandular tubule of the mucosa is supported by connective tissue only around the tubular portion. The generative cell zone in it appears to be tightly enclosed in a stromal sheath.3.Surface epithelial cells as well as parietal, mucous neck and chief cells lie outside the stromal sheath and these cell types do not incorporate3H-thymidine. Mucous neck cells that lie between parietal cells in the upper part of the gastric gland are morphologically similar to the undifferentiated cells of the constriction.4.From these results, it is suggested that undifferentiated proliferative cells confined to the stromal sheath, when free of the latter, grow and mature as they migrate. The parietal cell arises directly from the undifferentiated cell at the constriction, and it is suggested that the mucous neck cell is an immature form of the chief cell migrating from the generative cell zone.
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