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

Abstract

Orbital glands are found in many tetrapod vertebrates, and are usually separate structures, consisting of individual glands lying in the eyelids and both canthi of the orbit. In cetaceans, however, the orbital glandular units are less distinct and have been described by numerous authors as a single, periorbital mass. There are few histochemical and immunhistochemical studies to date of these structures. In this study, we examined the orbital glandular region of both the bowhead whale (Balaena mysticetus: Mysticeti) and the beluga whale (Delphinapterus leucas: Odontoceti) using histological, histochemical, and immunohistochemical techniques. Histologically, in the bowhead, three glandular areas were noted (circumorbital, including Harderian and lacrimal poles), palpebral (midway in the lower eyelid), and rim (near the edge of the eyelid). In the beluga, there was only a large, continuous mass within the eyelid itself. Histochemical investigation suggests neither sexual dimorphism nor age‐related differences, but both whales had two cell types freely intermingling with each other in all glandular masses. Large cells (cell type 1) were distended by four histochemically distinct intracellular secretory granules. Smaller cells (cell type 2) were not distended (fewer granules) and had two to three histochemically distinct intracellular secretory granules. The beluga orbital glands had additional lipid granules in cell type 1. Counterintuitively, both lipocalin and transferrin were localized to cell type 2 only. This intermingling of cell types is unusual for vertebrates in whom individual orbital glands usually have one cell type with one to two different secretory granules present. The heterogeneity of the orbital fluid produced by cetacean orbital glands implies a complex function, or series of functions, for these orbital glands and their role in producing the tear fluid.

Gross and histological morphology of the cervical gill slit gland of the pygmy sperm whale (Kogia breviceps)

“…The presence of lamellar corpuscles, resembling Pacinian corpuscles, also supports the hypothesis that the gland may experience changes in its volume. Pacinian corpuscles are mechanoreceptors associated with the somatosensory system that function in the detection of pressure changes and high frequency vibrations and can be used to perceive sound waves in water (Munger & Ide, 1987; Rehorek et al, 2020; Rehorek, Hillenius, Lovano, & Thewissen, 2018). There are rare reports of Pacinian corpuscles associated with glandular tissues in both humans and cetaceans.…”

“…In humans, Pacinian corpuscles have been demonstrated within the pancreas, prostate, and lymph nodes (Feito, Cobo, Santos‐Briz, & Vega, 2017; García‐Suárez et al, 2010; Pai, 2017; Standop, Ulrich, Schneider, Andrén‐Sandberg, & Pour, 2001). In cetaceans, Pacinian corpuscles have been demonstrated within the connective tissue surrounding the circumorbital glands of the bowhead whale ( Balaena mysticetus ) and along the entire course of the odontocete external auditory meatus (De Vreese et al, 2020; Rehorek et al, 2020). Intriguingly, the Pacinian corpuscles of cetaceans have been demonstrated to lack an outer core and capsule, and, therefore, only contain an inner core comprised of a central axon, surrounded by lamellae of Schwann cells, and a thin cellular layer (De Vreese et al, 2020).…”

Neuroanatomy of the Cetacean Sensory Systems

“…These lamellar corpuscles have also been described in spatial association with glandular structures in the cetacean skin and adnexa. As such, there are corpuscles in the stromal tissue of the circumorbital glandular region of bowhead whale ( Balaena mysticetus ) [ 153 ], in the subepithelial tissue in the cervical gill slit of the pygmy sperm whale ( K. breviceps ) [ 154 ], in the vicinity of the nasal glands in dolphins [ 151 ], and in the stromal tissue among the ear canal glands [ 152 ].…”