Harderian gland

The Harderian gland is an orbital gland found in many vertebrates. Its secretions and functions vary among species, including roles in lubrication, pheromone production, and immune defense.

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Orbit (anatomy): The bony cavity in the skull that contains the eye and associated structures. The gland lies within or near this cavity, depending on the species.
Holocrine secretion: A mode of secretion in which whole cells disintegrate to release their contents. Some Harderian glands, especially in rodents, release lipid-rich material through holocrine activity.
Pinealectomy: Surgical removal of the pineal gland. Studies compare pinealectomy with Harderian-gland removal to separate their effects on seasonal rhythms.
Rat: A rodent commonly used in biological and medical research. Rat Harderian glands are prominent, porphyrin-producing organs used in studies of secretion and circadian biology.
Lacrimal gland: An exocrine gland that produces the aqueous component of tears. It is another gland associated with the eye, but its secretions and distribution differ.
Porphyrin: A class of tetrapyrrole molecules that includes heme and related compounds. Porphyrins accumulate in the secretions of some rodents’ Harderian glands.
Circadian rhythm: An endogenous cycle of biological activity lasting about 24 hours. The gland’s indole production has been investigated in relation to daily timing.
Mouse: A small rodent widely used as a laboratory model organism. Mouse strains differ in Harderian-gland secretory characteristics and responses to physiological conditions.
Nictitating membrane: A translucent or opaque third eyelid found in many vertebrates. In some species, the Harderian gland is associated with this membrane and helps lubricate it.
Melatonin: A hormone that helps coordinate circadian and seasonal physiology. Melatonin and related indoles occur in the Harderian gland of some mammals.