Ultrastructural aspects of calf submandibular glands

Submandibular gland biopsies from four calves were examined by electron microscopy. Most of the parenchyma consists of mucous acini capped by seromucous demilunes. Secretory product of the demilunes reaches the acinar lumen via intercellular canaliculi located between adjacent demilunar cells or by narrow apical extensions of demilunar cells bordering the lumen in common with acinar cells. Intercellular canaliculi are absent between mucous acinar cells, but intercellular space is present at junctions of demilunar cells, acinar cells, and intercalated duct cells. Intercalated ducts are short and connect mucous acini with striated ducts. Striated ducts show more basal infoldings and mitochondria than those of bovine parotid glands. Nuclear bodies are present in most epithelial cell types of the gland but are larger and more easily recognized in nuclei of striated duct cells. Attempts are made to correlate the structure of bovine submandibular glands with its secretion of small amounts of hypotonic saliva relative to the larger volume of isotonic saliva secreted by parotid glands of the same animal.