Pineal gland

Definition
noun, plural: pineal glands
A small endocrine gland shaped like a pinecone, located in the epithalamus, and involved in melatonin production
Supplement
The pineal gland is a small endocrine gland. It resembles a pinecone in terms of shape (thus, the name). In humans, it is reddish-gray in color and about 5 to 8 mm in size. It is comprised mainly of pinealocyte (i.e. a cell body with 4 to 6 processes). Other cell types found in the pineal gland include neuronal-like peptidergic cells, pineal neurons, perivascular phagocytes, and interstitial cells.
The pineal gland is located in the epithalamus, near the center of the brain. Its main function is associated with the production of melatonin. Melatonin is a hormone involved in the regulation of biorhythms, colour changes in the skin of reptiles, and reproductive cycles in mammals.
Almost all vertebrates have a pineal gland. Examples of animal species that lack a pineal gland are hagfish and lancelet Branchiostoma lanceolatum. The hagfish though may have an equivalent structure for the pineal gland in the dorsal diencephalon.¹
Synonym(s):

• pineal body
• conarium
• epiphysis (cerebri)
• conarion
• pineal organ

See also:

pineal eye

melatonin

photoreceptor

great cerebral vein

Reference(s):

¹ Ooka-Souda, S., Kadota, T., and Kabasawa, H. (December 1993). “The preoptic nucleus: the probable location of the circadian pacemaker of the hagfish, Eptatretus burgeri”. Neurosci. Lett. 164 (1–2): 33–6.