Charlie Derbyshire and Oliver Dorfner The Pineal Gland Charlie Derbyshire and Oliver Dorfner

Location of the Pineal Gland The Pineal Gland is located inside the brain next to the hypothalamus.

Melatonin The hormone melatonin is the main hormone released by the pineal gland and prepares the brain for sleep. Melatonin production of the pineal gland is regulated by sensors in the retina that detect lack of daylight. This means that melatonin is only produced in the dark, which is why it’s hard to go to sleep in light. Melatonin controls our circadian rhythms, and allows us to detect when it’s day or night. It can also use the relative lengths of day and night to determine seasonal changes, much like phytochrome in plants. Melatonin is also thought to induce bone deposition.

Regulation of Melatonin Production Light-sensitive neurons in eyes are stimulated by daylight, and send a signal to the suprachiasmatic nucleus(SCN). The SCN then decides if it is daylight, and, if it is, sends a signal to the paraventricular nuclei(PVN). The PVN then sends on the superior cervical ganglia(SCG), which then sends a signal to the pineal gland to start production of melatonin.

The Pituitary and Pineal Glands Recent studies have proposed that the pituitary glands’ production of FSH and LH are regulated by the pineal gland. However, addition of melatonin did not affect pituitary production of FSH or LH, so another unknown hormone may be regulating this production.

Evolution of the Pineal Gland In most mammals, the pineal gland is believed to be an evolutionary remnant of an ancient “third eye”, called the parietal eye. This eye couldn’t see, but was photoreceptive. This photoreceptive structure still exists in reptiles, sharks, bony fish, salamanders, and frogs, being small, hard to see, and covered with skin. Looking back in the fossil record, very early vertebrates had a notch in their skulls where a third eye could have resided. The skull structure of some reptiles still reflects this. The lamprey, one of the most ancient vertebrates, possesses a pineal eye. It is believed that the structure of its eyes were once widespread.

Feedback Loops Melatonin receptors are present on the suprachiasmatic nuclei of most species, suggesting that the secretion of melatonin is regulated by a negative feedback loop. This is important to keep melatonin from building up, causing constant drowsiness.

Disease A pineal germinoma is the most common type of tumor that forms in the pineal gland. Signs of one include premature puberty, Parinaud’s syndrome (the inability to move eyes up and down), insomnia, and vomiting. If gone undiagnosed, a pineal germinoma can lead to difficulty walking and water in the brain. If diagnosed early, survival rate with chemotherapy and radiation is relatively high, at 90%.

Sources: http://www.1800remedies.com/how-to-clean-up-the-pineal-gland/ http://www.knowcancer.com/tumor/pineal-germinoma/ https://www.scienceabc.com/nature/animals/can-animals-have-a-third-eye.html http://thebrain.mcgill.ca/flash/a/a_11/a_11_cr/a_11_cr_hor/a_11_cr_hor.html https://jonbarron.org/article/endocrine-system-hypothalamus-pituitary-pineal-glands