Comparative morphology of esophageal mucosa and submucosa in dogs from 1 to 337 days of age.

: Scanning electron microscopy, light microscopy, and morphometric analyses were used to examine the morphology of the tunica mucosa-tela submucosa of the cervical, thoracic, and abdominal parts of the esophagus of healthy dogs from birth to 337 days of age from 3 litters of dogs whelped and reared under controlled conditions. Apart from the absence of a lamina muscularis mucosae from the cervical part of the esophagus of all dogs examined, little regional variation was detected. However, morphologic variation associated with age was observed. The number and complexity of microplicae on surface epithelial cells, as observed with the scanning electron microscope, increased with age, particularly between 1-day-old and 21-day-old dogs. Although scanning electron microscopy revealed typical duct openings from the submucosal glands in 1-day-old dogs, light microscopy revealed few functional glands. These glands gradually developed into a complex strata of tubules and acini during the time that secretory activity and the volume fraction of the tunica mucosa-tela submucosa occupied by glands increased with age. The presence of ciliated cells in the esophagus of 1-day-old dogs was apparent with scanning electron and light microscopes. Ciliated cells were always most abundant in the abdominal part of the esophagus. Finally, morphometric analyses revealed a significant increase in epithelial and connective tissue compartment thicknesses, as well as a marked increase in the volume fraction occupied by glands between 1 day and 161 days after dogs were whelped. A smaller decrease in all 3 measures occurred between 161 and 337 days after the dogs were whelped.