Dynamic histology of the antral epithelium in the mouse stomach: IV. Ultrastructure and renewal of gland cells.

The renewal of gland cells was investigated by three-dimensional reconstruction of typical mucous units of the pyloric antrum using electron microscopy and 3H-thymidine radioautography in 3 to 4 month-old CD1 mice. Based on analysis of 42 units, the average gland measured 31 micron in length and was composed of 37 (mucous) gland cells with eight enteroendocrine cells scattered among them. The gland neck cells located close to the isthmus showed the cytoplasmic and nuclear features characteristic of differentiating cells. The mid-gland cells occupying the central portion of the gland appeared to be at a more advanced stage of development and completing differentiation. The gland base cells comprising the blunt end of the gland were fully mature. To quantify the renewal process, the percent of gland cell nuclei carrying label was determined at several times following 3H-thymidine administration. The rate of proliferation was found to be greatest in the gland neck, lower in the mid-gland, and even lower within the gland base. Furthermore, the isthmus contributed to gland-cell renewal by providing an estimated 12.4 cells per day. Labeled cells migrated toward the blunt end of the gland. The migration rate became progressively slower with their descent, and many cells were lost along the migration pathway, mainly in the gland neck. The loss took place without being preceded by gradual cell degeneration, but occurred as a result of rapid extrusion to the lumen or, less frequently by pyknosis, which could be followed by phagocytosis. It is concluded that the rapid rate of mitosis within the isthmus and gland neck generates a pressure causing downward migration of the cells toward the blunt end of the gland. The rate of migration, however, gradually diminishes as cells descend into the gland, presumably owing both to decreasing proliferation rate and to cell loss. Thus, while cells migrate down toward the gland base, many are lost before reaching it. This sequence is described as "the cascade pattern" of renewal.