Pineal Gland

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Pineal Gland

Looking At Life Through The Third Eye

All living things, from the most primitive to the most developed, continue their vital activities in a certain rhythm. Sleep-wake states, reproductive times, hunting and eating habits and their physiological, biological and psychological rhythms. We examine these ongoing events under the title of “circadian rhythm” as the world takes a complete tour around its axis (2). When we investigate the circadian rhythm in mammals, the first thing we will look at is the Pineal Gland and the Melatonin Hormone it produces (3).

The Pineal Gland has been the subject of research many times in people’s lives for centuries with its mystery and unknowns. Dozens of theories have been put forward for the Pineal Gland since Ancient Times. Most philosophers, mathematicians, religious people, anatomists believed that the Pineal Gland was ‘the place where the soul meets the body’ many were wrong in explaining its anatomical structure. However, these illusions and unknowns did not prevent continuing the research. We can understand Saint Augustine’s idea that the soul is connected to the whole body by saying “in each body the whole soul is in the whole body, and whole in each part of it” (4). The concept of “seat of the soul” for the Pineal Gland by famous French philosopher Rene Descartes, is one of the most impressive descriptions ever (5).

So what is the Pineal Gland, which actually has a very romantic history with descriptions such as ‘the eye of Horus (Wadjet)’, ‘the third eye of Shiva’, ‘seat of the soul’, ‘the place where the soul meets the body’?

Image 1: Rene Descartes’ ‘seat of the  soul’

Image 1: Rene Descartes’ ‘seat of the soul’.

Image 2: The third eye of Shiva

Image 2: The third eye of Shiva.

Image 3: Comparison of the pineal gland and the eye of horus

Image 3: Comparison of the pineal gland and the eye of Horus.

Pineal Gland origin comes from the Latin “Glandula Pinealis”. Pineal got its name from the pine cone it resembles. Also known as The Epiphysis cerebri and Pineal Body. It is part of the epithalamus, which is part of the diencephalon. The Pineal Gland is a neuroendocrine gland that lies in the center of the brain, behind the third ventricle, below the corpus callosum (6,7).

Functions of the Pineal Gland

  • The most important function of this gland is to maintain the circadian rhythm and regulate the sleep-wake cycle. It provides this with the melatonin hormone (N-acetyl-5-methoxytryptamine) it secretes.The cells that secrete the Melatonin hormone in the epiphysis are ‘pinealocytes’. Pinealocyte cells secrete melatonin in the dark, as they are sensitive to light. (6, 7)
  • The light factor has the power to suppress melatonin secretion and change the time of the rhythm in mammals.(8)
  • Melatonin production is inversely proportional to the amount of light falling on the retina. (6)
Image 4: The melatonin hormone's relation to light.

Image 4: The melatonin hormone’s relation to light.

Image 5: a brain section showing the pineal gland.

Image 5: A brain section showing the pineal gland.

  • As we know, our brain is protected through the blood-brain barrier. Interestingly, however, the pineal gland is not isolated from this barrier. Therefore, as the gland increases melatonin secretion, the hormone enters the bloodstream through passive diffusion (6,7)
  • Besides melatonin, it also produces several indoleamine and polypeptide hormones (6). A common example of indolamine is the tryptophan derivative serotonin, which is the mood and sleep-related neurotransmitter (9).
  • The pineal gland controls the maturation of the genitals at the right time (puberty) (6).
  • It regulates seasonal reproductive cycles. These seasonal changes are regulated by photoperiodic acting through the circadian system (10).
  • Pineal gland hormones often inhibit the activity of other endocrine glands (6).
  • One of the striking features of melatonin is that the disruption of the circadian rhythm of melatonin causes mood disorders (11).
  • Melatonin, which is also taken as a nutritional supplement, has not yet been observed to have any serious side effects (12).
 Image 6: Melatonin, which is thought to affect many vital events from cancer to reproduction, also has certain evidences in this regard.

Image 6: Melatonin, which is thought to affect many vital events from cancer to reproduction, also has certain evidences in this regard.

Image 7: Chemical formula of melatonin

Image 7: Chemical formula of melatonin.


  2. “What makes us sleep?”. NICHD – Eunice Kennedy Shriver National Institute of Child Health and Human Development. Retrieved 6 May2019.
  3. Benloucif, S., Guico, M. J., Reid, K. J., Wolfe, L. F., L’Hermite-Balériaux, M., & Zee, P. C. (2005). Stability of melatonin and temperature as circadian phase markers and their relation to sleep times in humans. Journal of biological rhythms20(2), 178-188.
  4. On the Trinity, book 6, ch. 6
  5. Descartes, R. (1984). The Philosophical Writings of Descartes: Volume 2(Vol. 2). Cambridge University Press.
  7. Fung, B. K. K. (1987). Transducin: structure, function and role in phototransduction. Progress in retinal research6, 151-177
  8. Lewy, A. J., Wehr, T. A., Goodwin, F. K., Newsome, D. A., & Markey, S. P. (1980). Light suppresses melatonin secretion in humans. Science210(4475), 1267-1269
  10. Becker-André, M., Wiesenberg, I., Schaeren-Wiemers, N., Andre, E., Missbach, M., Saurat, J. H., & Carlberg, C. (1994). Pineal gland hormone melatonin binds and activates an orphan of the nuclear receptor superfamily. Journal of Biological Chemistry269(46), 28531-28534
  11. Selvi, Y., Beşiroğlu, L., & Aydın, A. (2011). Kronobiyoloji ve duygudurum bozuklukları. Psikiyatride Güncel Yaklaşımlar3(3), 368-386
  12. NORDLUND, J. J., & LERNER, A. B. (1977). The effects of oral melatonin on skin color and on the release of pituitary hormones. The Journal of Clinical Endocrinology & Metabolism45(4), 768-774

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