An electron microscopic study of esophageal epithelium in the newborn and adult mouse

The stratified squamous epithelium of the esophagus in the newborn and adult mouse was studied by histological, histochemical and electron microscopic methods. In the newborn, the cells located above the basal layer elaborate mucus. The relative abundance of Golgi zones and rough-surfaced endoplasmic reticulum suggests the involvement of these organelles in the production of mucous granules. The membrane of mature mucous granules ruptures and their contents become dispersed in the cytoplasm. Mature mucous granules are not seen in the outermost cells which are about to be exfoliated. The process of exfoliation begins in the upper layer of the epithelium when the contiguous cell membranes separate and wide intercellular spaces are formed. While the cells reach the surface, the intercellular spaces widen, the cells lose contact and are shed. The distal surfaces of the cells in the upper layer are lined by a surface coat which consists of finely branched filaments. The esophageal epithelium of the adult mouse is similar to the epidermis and undergoes complete keratinization. The sequential development of differentiation products, namely the cytoplasmic filaments, membrane-coating granules (MCG) and keratohyalin granules is seen as the cells migrate toward the surface. After their formation, MCG migrate toward the cell surface where they become confluent with the plasma membrane and are secreted into the intercellular space. Keratohyalin granules are also elaborated in large numbers and become dispersed as the cells become cornified. As the horny cells are formed the cell constituents such as the rough-surfaced endoplasmic reticulum, Golgi complex, ribosomes, mitochondria and the nucleus disintegrate. The fully keratinized cell has a thickened envelope and is filled with filaments embedded in an amorphous matrix.