The pineal gland is a small endocrine gland in the brain that mainly controls the circadian rhythm, or sleep-wake rhythm of the body via the hormone melatonin and serotonin in alternation. The pineal gland is of enormous importance because it not only controls many bodily functions depending on the time of day, but the hormonal interplay also has enormous effects on the psyche.
What is the pineal gland?
The pineal gland (glandula pinealis), also called the epiphysis, is a small endocrine gland about 5 – 8 mm long and 3 to 5 mm thick, reminiscent in appearance of small pinecones or tiny pinecones. The pineal gland is located directly on the epithalamus and controls the circadian rhythm by synthesizing melatonin during the night when it is dark. Melatonin is synthesized from serotonin in the pineal gland during tryptophan metabolism and released into the blood. Exposure to light stops melatonin production. During the deep sleep phases, which are also controlled by melatonin, the alpha cells of the anterior pituitary (HVL) are stimulated to release the growth hormone somatropin (also somatotropin). The day-wake rhythm, which is controlled by melatonin, has a major influence on many organ functions, including the course of the pubertal phase, which, if the circadian rhythm is disturbed, can begin too early with the consequence of sexual precociousness or can delay or impede sexual maturation altogether.
Anatomy and tasks
The pineal gland is a small endocrine gland located in the diencephalon directly adjacent to the epithalamus. The pineal gland is composed mainly of secretory cells (pinealocytes), which secrete the hormone melatonin into the bloodstream in darkness, and glial cells, which perform some supporting function and provide electrical insulation between neurons. In addition to melatonin, the gland also secretes neuropeptides, the effects of which are still largely unexplored. Already at the age of less than 20 years, the pineal gland shows first signs of calcification. Glial cells proliferate and glandular cell tissue is degraded. Small cysts form, into which calcium and magnesium salts are deposited, forming small plaques. Medically, the plaques that are visible in the X-ray image are called brain sand or acervulus. The significance of the brain sand has not yet been conclusively researched. Since the pineal gland adjusts its circadian rhythm according to the incidence of light, among other things, evolution had to create a device that informs it of the prevailing light conditions at any given time. The pineal gland receives light signals that first travel from the retina via the optic nerve to the suprachiasmatic nucleus in the hypothalamus and from there continue to the spinal cord. They travel back up the brain via other nodes to the pineal gland.
Function and tasks
In addition to the nucleus suprachiasmaticus in the hypothalamus, which is the primary center for chronobiological processes in the body, the pineal gland has the task of synchronizing the day-night rhythm, “fine-tuning” it, so to speak. Depending on the incidence of light in the eyes, it adjusts the genetically pre-programmed circadian rhythm, which can deviate upwards or downwards from 24 hours, to the actual day-night conditions. The neurotransmitter melatonin has a wide-ranging effect on the function of many organs, whose activity is controlled accordingly. For example, kidney function, heart rate, blood pressure, body temperature and many other organ activities are controlled via the neurotransmitter. In women, melatonin stimulates the release of FSH (follicle-stimulating hormone) and LH (luteinizing hormone). Both hormones promote maturation of eggs in the ovaries, and in men, the hormones promote sperm production and sperm maturation in the testes. Hormone production reaches a peak at night – around two to three o’clock – and then drops rapidly again as soon as there is an incidence of light via the eyes, whereby the closed eyes also perceive the light and “report” it to the pineal gland. The mechanism also works in blind people. The function of the pineal gland as a synchronizer of the circadian rhythm is particularly important in the case of a change of time zones, e.g. during long-distance flights in east-west or west-east direction.
Diseases and ailments
Diseases and disease symptoms associated with the pineal gland may involve the endocrine tissue of the gland itself, or they may involve benign or malignant tumors that are located in close proximity to the gland and cause symptoms through the physical pressure they exert on the surrounding tissue. Within the overall rare tumors associated with the pineal gland, the so-called pineal cysts are relatively common. These are benign cysts that arise from the pineal gland and are often accompanied by symptoms such as headaches, nausea, visual disturbances, or even balance disorders. If large enough, they can lead to a buildup of cerebrospinal fluid, which can cause the development of hydrocephalus. Pinealis cysts usually occur in childhood to early adulthood and can be visualized on MRI. A fairly rare tumor that originates directly from the melatonin-producing cells of the pineal gland, the parenchymal cells, is pinealoblastoma. It is a malignant tumor that produces symptoms of increased intracranial pressure at an early stage. More commonly, tumors in the pineal region are germ cell tumors, which are almost always benign in women and more likely to be malignant in men. It has not yet been conclusively researched which triggering factors are responsible for the development of the tumors. In recent years, research projects have found indications for a certain genetic disposition. Defined gene mutations seem at least to be possible trigger factors.