The pineal gland, also known as the pineal body, conarium or
epiphysis cerebri, is a small endocrine gland in the vertebrate brain. The
shape of the gland resembles a pine cone, hence its name. The pineal gland is
located in the epithalamus, near the center of the brain, between the two
hemispheres, tucked in a groove where the two halves of the thalamus join. The
pineal gland produces melatonin, a serotonin derived hormone which modulates
sleep patterns in both circadian and seasonal cycles.Nearly all vertebrate
species possess a pineal gland. The most important exception is the hagfish,
which is often thought of as the most primitive extant vertebrate. Even in the
hagfish, however, there may be a "pineal equivalent" structure in the
dorsal diencephalon. The lancelet Branchiostoma lanceolatum, the nearest
existing relative to vertebrates, also lacks a recognizable pineal gland. The
lamprey (considered almost as primitive as the hagfish), however, does possess
one. A few more developed vertebrates, including the alligator, lack pineal
glands because they have been lost over the course of evolution.
The results of various scientific research in evolutionary
biology, comparative neuroanatomy and neurophysiology, have explained the phylogeny
of the pineal gland in different vertebrate species. From the point of view of
biological evolution, the pineal gland represents a kind of atrophied
photoreceptor. In the epithalamus of some species of amphibians and reptiles,
it is linked to a vestigial organ, known as the parietal eye which is also
called the third eye. René Descartes believed the pineal gland to be the
"principal seat of the soul" (a mystical concept). Academic
philosophy among his contemporaries considered the pineal gland as a
neuroanatomical structure without special metaphysical qualities; science
studied it as one endocrine gland among many. However, the pineal gland
continues to have an exalted status in the realm of pseudoscience.
By
Kokilavani
III B.SC-Biochemistry (14UBC024)
Department of Biochemistry
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