The pineal gland is located near the center of the brain, between the two hemispheres, tucked in a groove where the two rounded thalamic bodies join. It is about the size of a grain of rice (5–8 mm)
It produces the serotonin derivative melatonin; a hormone that affects the modulation of the wake/sleep patterns and seasonal functions secretes the hormone melatonin, which is involved in the body's sleep wake cycle.
Pineal activity lessons in the bright light, so melatonin levels are lower during the day. They rise at night, increasing about tenfold, making us sleepy. Bright light does not directly affected the pineal gland: instead, input from the visual pathways stimulate the suprachiasmatic nucleus (part of the hypothalamus), which sends signals to the pineal gland via nerve connections near the spinal cord. Light exposure to the retina is first relayed to the suprachiasmatic nucleus of the hypothalamus, an area of the brain well known to coordinate biological clock signals. Fibers from the hypothalamus descend to the spinal cord and ultimately project to the superior cervical ganglia, from which post-ganglionic neurons ascend back to the pineal gland. Thus, the pineal is similar to the adrenal medulla in the sense that it transduces signals from the sympathetic nervous system into a hormonal signal.
The suprachiasmatic nucleus also controls other diurnal biological rhythms, such as body temperature and appetite, and it is likely that melatonin cycles influence these processes. Melatonin is also an anti-oxidant and may protect against damage from free radicals in the body.
Melatonin also reduces cortisol output to its lowest levels of the day so we do not burn nor require calories at night. This slows our metabolism so good rest and sleep can be achieved. High melatonin can reduce cortisol too much just as low melatonin can allow high night time cortisol levels which disturb sleep patterns.
The human pineal gland grows in size until about 1–2 years of age, remaining stable thereafter, although its weight increases gradually from puberty onwards. The abundant melatonin levels in children are believed to inhibit sexual development, and pineal tumors have been linked with precocious puberty. When puberty arrives, melatonin production is reduced. Calcification of the pineal gland is typical in adults.
Melatonin has important effects in integrating photoperiod and affecting circadian rhythms. Consequently, it has been reported to have significant effects on reproduction, sleep-wake cycles and other phenomena showing circadian rhythm.
As pineal gland cysts are often asymptomatic or without symptoms, they are mainly discovered in CT and MRI scans carried out to diagnose some unrelated conditions or disorders. They are more frequently detected in autopsies performed after death. However, larger cysts that produce symptoms may require neurological evaluation and can be detected with the help of a brain scan. Usually, pineal cysts can be easily distinguished by their characteristic appearance from the tumors that develop in the pineal region.
Unless the pineal gland cysts are growing and large enough to cause hydrocephalus by blocking the cerebral aqueduct, they do not require any treatment. This is because these cysts are harmless and benign or non-cancerous. However, in rare cases, surgical removal of these cysts may be required, if they are very large and are producing severe symptoms that can affect the health and well-being of an individual. But like any other brain surgery, this process also involves some risks. For less severe conditions, medications are prescribed to alleviate the symptoms.
Only in rare cases do pineal gland cysts cause any serious health problem. No specific reasons behind the formation of these cysts have been discovered till now. But it is important to regularly monitor the size of these cysts once they have been detected. This will help find out if the cysts are growing in size and posing any health hazard for that individual.