Orbital gland structure and secretions in the Atlantic bottlenose dolphin (Tursiops truncatus)

Abstract

Orbital gland structure of the Atlantic bottlenose dolphin, Tursiops truncatus, was examined at the macroscopic, light microscopic, and electron microscopic levels. The gland completely encircles the ocular globe in a belt-like fashion near the conjunctival fornix but is considerably more developed medially. Duct openings are scattered throughout the fornix and over the surface of the palpebral conjunctiva. Microscopically, the gland has a tubuloalveolar arrangement; alveolar cells contain numerous secretory vesicles which can be interpreted as two structural types by light and electron microscopy. Histochemical staining demonstrates that both types contain glycosaminoglycans. Lipid analysis of the glandular secretion (dolphin tears) shows them to be non-oily and to contain only negligible amounts of cholesterol, triglycerides, phospholipids, and free fatty acids. The secretion is clear, slippery, and viscoelastic and well-adapted to protecting the eye and to reducing frictional forces between the eye surface and surrounding seawater.

Morphology of accessory structures of the humpback whale (Megaptera novaeangliae) eye

“…In Bottlenose dolphins ( Tursiops truncatus ), the Harderian gland completely surrounds the eyeball and is more developed medially (Tarpley and Ridway ). In other animals, this gland can be thick and fill the area between the orbit wall and the eyeball (Waller and Harrison ), as observed in our study.…”

Whale tear glands in the bowhead and the beluga whales: Source and function

“…Histologically, the orbital glands of cetaceans are poorly described in the literature. The presence of a distinct non‐secretory duct system has been previously described in Tursiops truncatus (Tarpley & Ridgway, ) and three species of balaenopterid whales (common minke whale [ Balaenoptera acutotostrata ], sei whale [ Balaenoptera borealis ], and Bryde's whale [ Balaenoptera edeni ]: Funasaka et al, ). This duct system is restricted to the larger glandular masses (lacrimal, Harderian, and palpebral glands) and not the smaller, intervening diffuse glandular mass.…”

“…There is much disparity in the literature regarding cetacean orbital gland nomenclature and distribution (see Rehorek et al, for review). Some published reports refer to a singular large, circumorbital gland as the orbital (Tarpley & Ridgway, ) or the Harderian (Bodyak & Stepanova, ; Funasaka et al, ; Ortiz et al, ) gland. Other authors identify groups of two to three individual glands that include the Harderian, lacrimal, and intervening conjunctival glands (Pütter, ; Rodrigues et al, ; Waller & Harrison, ; Weber, ).…”

“…Funasaka et al () showed that balaenopterid orbital glands possess secretory cells that are positive for both acidic and neutral glycosaminoglycans, although other cell types were not specified. Other descriptions identify multiple histochemically (Tarpley & Ridgway, ) or ultrastructurally (Bodyak & Stepanova, ; Ortiz et al, ; Waller & Harrison, ) characterized cell types, but do not identify specific anatomical sites within the glandular mass. Our study identified two histologically and histochemically distinct cell types in the bowhead and the beluga (large cell type 1 and small cell type 2).…”

“…The palpebral glands, however, are usually described as a singular glandular mass, and are not separated into multiple smaller glands as described in terrestrial mammals (see Rehorek et al, for review). Histochemically, these glands in cetaceans are described as homogeneous and mucoserous (Funasaka, Yoshioka, & Fujise, ; Tarpley & Ridgway, ; Waller & Harrison, ). Lipid granules have been described in the female Harderian gland of the dolphin ( Tursiops truncatus : Bodyak & Stepanova, ) and is one of the few mammalian instances of sexual dimorphism in the Harderian gland outside of rodents (Payne, ).…”