Histology, histochemistry and fine structure of the lacrimal gland in the one-humped camel (Camelus dromedarius)

Abstract

Our research aimed to provide complete histological, histochemical and ultrastructural features of the lacrimal gland of the one-humped camel (Camelus dromedarius) as well as novel insights into its adaptability to the Egyptian desert. Our study was applied to 20 fresh lacrimal glands collected from 10 camels instantly after their slaughtering. The results revealed that the gland was a compound tubulo-acinar gland, and its acini were enclosed by a thick connective tissue capsule that was very rich in elastic and collagen fibres. The gland acini had irregular lumens and were composed of conical to pyramidal cells. The nuclei of secretory cells were found in the basal part, and the cytoplasm was eosinophilic and granular. The glandular tissue consisted of serous and mucous acini and seromucous secretory cells. Histochemically, there was a significant amount of neutral mucopolysaccharides in the acini in which mucous cells had a significant periodic acid-Schiff (PAS)-positive reaction, whereas seromucous cells had a mild PAS-positive reaction. Ultrastructurally, the lacrimal cells had numerous secretory vesicles with contents of moderately to highly electron-dense cytoplasm. The nuclear envelope consisted of two prominent membranes surrounding the peri-nuclear cisterna. The acinar cells had numerous electron-lucent and moderately electron-dense secretory granules, mainly situated on the apical surface, and secreted their contents into the lumen. The luminal surface of the mucous secretory cells represents the remains of secretory granules discharged by the merocrine mechanism. In conclusion, the mucous secretion is believed to aid in the washing and moistening of the eyeball, particularly in dry, hot and dusty environments.