Epiphysis
How does melatonin affect us?
The epiphysis is an appendage of the brain that produces hormones. It is also called the third eye. In some ancient reptiles, a third eye was found on the crown – the epiphysis, which perceived light directly. Now such animals are extinct, the body perceives light through the retina of the eye, and through the retinohypothalamic tract, the signal about illumination is transmitted to the epiphysis. In the dark, the epiphysis produces the hormone melatonin. As a result of the production of this hormone, the body changes its functioning depending on the time of day.
In different seasons, the duration of the dark and light period of time varies, the production of melatonin also changes. This is related to the regulation by melatonin of the seasonality of reproduction in mammals, since, unlike humans, mammals reproduce seasonally. At the end of pregnancy and at the birth of the fetus, there should be sufficient resources in the environment to feed the cub. In humans, the seasonality of reproduction is lost, because we live under artificial lighting. The seasonality of reproduction is also lost in laboratory animals: melatonin in such animals is produced at night.
At night, melatonin regulates the production of hormones, which are also produced in different concentrations depending on the time of day, so that the body functions differently at night or during the day. The connection of melatonin with the seasonality of reproduction and with differences in the functioning of the body at night and during the day is one of the main functions of melatonin. There are melatonin preparations that help to tolerate jet lag during a long flight: taking melatonin simulates night time, helps the body relax and fall asleep. This property of melatonin turns it into a negative regulator of sexual development. While there is a lot of melatonin, sexual development does not begin. It inhibits the development of gonads – the gonads. In adult animals, melatonin is activated during the non-breeding season. In children, it suppresses the development of the sex glands until they reach a certain age. When children reach puberty, the epiphysis reduces melatonin production. This serves as an impetus to the beginning of puberty, the work of the sex glands, the work of the pituitary gland and hypothalamus is activated.
Melatonin got its name due to another function. When it was discovered, it turned out that it causes skin lightening in lower vertebrates due to the concentration of pigment around the cell nucleus. This is partially manifested in many children: in blondes, during puberty, the hair darkens, because the concentration of melatonin decreases and its effect on the lightening of the integument decreases. Macrogenitosomy is a tumor of the epiphysis, it often appears in boys aged 5-6 years. Tumor cells replace normal epiphysis tissue, and the concentration of melatonin begins to decrease. Melatonin in the blood becomes low, and premature puberty begins in sick children. This process leads to early termination of growth, therefore, children who develop macrogenitosomy are small in stature, but their genitals are developed like an adult. Hence the name – macrogenitosomy: the disproportionate size of the genitals compared to the size of the body. Early cessation of melatonin production leads to early puberty.
Other functions of melatonin are also important. Melatonin is a strong immune modulator and affects the functions of the immune system. It participates in the regulation of cell proliferation and has an anti-carcinogenic effect. It is important to remember that melatonin is produced from serotonin, which is also a biologically active compound. If in other parts of the brain biosynthesis goes to serotonin, then in the epiphysis serotonin turns into melatonin. These reactions of conversion of serotonin into melatonin are regulated by enzymes. Scientists also studied the question of why melatonin production increases at night. It turned out that N-acetyltransferase is an enzyme involved in the final production of melatonin, it also has diurnal fluctuations. A change in the activity of this enzyme leads to the fact that melatonin is produced more at night than during the day.
Unlike other endocrine glands, the regulation of melatonin production occurs due to nerve connections. Although melatonin is located under the quadrilateral of the brain, it is not directly regulated by the central nervous system. The neural pathways that are involved in the regulation of melatonin production start from the retina, because through it melatonin receives signals about changes in illumination. These signals pass through the retinohypothalamic tract, and then, with the help of the sympathetic nervous system, the production of melatonin is regulated. One of the nuclei of the brain, the suprachiasmatic nucleus, participates in the rhythmic production of melatonin. It is important in the regulation of various rhythms in the body.
The diverse functions of melatonin suggested that it plays a role in the regulation of life expectancy. Both the aging of the epiphysis, which begins after puberty, and the change in melatonin production lead to aging of the entire body. With aging, the reactions of melatonin to illumination change, and its production shifts compared to the normal change of day and night. Elderly people do not fall asleep well, go to bed earlier, get up later due to the fact that they have a disturbed rhythm of melatonin production. Seasonal diseases are known in humans, for example, exacerbations of diseases of the nervous system. And these seasonal exacerbations are associated with abnormal production of melatonin, an incorrect schedule of its production during the day. In seasons when the illumination changes, the body reacts incorrectly to this, as a result of which various diseases worsen. The rhythms of day and night are important for normal body functions, so if some functions suffer, then changes in melatonin production are also superimposed on this.
About the author:
Olga Smirnova – Doctor of Biological Sciences, Professor of the Department of Human and Animal Physiology, Head of the Laboratory of Endocrinology of the Faculty of Biology of Lomonosov Moscow State University.
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