CYTOARCHITECTURE OF THE BOVINE PYLORIC EPITHELIUM DURING EARLY ONTOGENY

The cytoarchitecture of the pyloric gland region in the early ontogeny of the bovine abomasal mucosa was investigated using light and transm ission electron microscopic methods. Two cell types are involved in fo rming 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 cel l and the brush cell. The indifferent cell represents the first stem c ell, which develops into the secretory granule-containing cell type. T his seems to be the secondary stem cell lining the top of the epitheli um as well as the base of the primitive epithelial tubes, and it diffe rentiates into the surface mucous cell and the pylorocyte. Endocrine c ells appear as open and closed types and represent the most differenti ated cells already present in the youngest specimen in this investigat ion. The most rare cell type, the brush cell, appears in the bovine ab omasal ontogeny much earlier than in other mammalian species.