Cytoarchitecture of the bovine pyloric epithelium during early ontogenesis.
The cytoarchitecture of the pyloric gland region in the early ontogeny of the bovine abomasal mucosa was investigated using light and transmission electron microscopic methods. Two cell types are involved in forming the lamina epithelialis in the youngest fetus with a 24 mm crown-rump-length (CRL): the indifferent cell and the endocrine cell. With a CRL of 71 mm, two other cell types occur, the granule-containing cell and the brush cell. The indifferent cell represents the first stem cell, which develops into the secretory granule-containing cell type. This seems to be the secondary stem cell lining the top of the epithelium as well as the base of the primitive epithelial tubes, and it differentiates into the surface mucous cell and the pylorocyte. Endocrine cells appear as open and closed types and represent the most differentiated cells already present in the youngest specimen in this investigation. The most rare cell type, the brush cell, appears in the bovine abomasal ontogeny much earlier than in other mammalian species.