Menstruation is a completely cyclical and normal process for the female body, during which the functional layer of the lining of the uterus is shed. It is, however, subject to ultra-fine regulation coming from 5 levels. The cerebral cortex, hypothalamus, pituitary gland, ovaries and endometrium are interconnected in a neuro-endocrine axis, the stability and integrity of which determine the cyclicity of menstruation. The cerebral cortex and other structures of the central nervous system, such as the reticular formation and visual analyzer, rather have an indirect effect on the reproductive system. Their stimuli, such as stress, an affected emotional situation, disturbances in the day-night rhythm (circadian rhythm), characteristic of life situations such as a common cold, an intercontinental flight, a change from a night to a day work shift make the menstrual cycle cyclolabile, i.e. irregular. The next level of regulation is the hypothalamus, which secretes a hormone called gonadoliberin. It stimulates the floor further down the imaginary axis, namely the anterior lobe of the pituitary gland, which secretes two hormones in the form of pulse secretion – follicle-stimulating (FSH) and luteinizing (LH). The sharp increase in their concentration in the bloodstream is a stimulus for the production of female sex hormones from the ovary, which are estrogens and progesterone. Another process that takes place in parallel with the synthesis of sex hormones is the formation of a dominant follicle in the ovary with dimensions over 20 mm. In fact, its burst, stimulated by the LH peak in the middle of the menstrual cycle, is referred to as ovulation. NEWS_MORE_BOX From this moment on, the ovary begins to produce more progesterone than estrogen, the effect of which is at the last level in the regulation of the menstrual cycle – the endometrium (the lining of the uterus). Sex hormones have a specific effect on the functional layer of the uterine mucosa. In the first phase of the cycle, which is dominated by ovarian estrogen production, the endometrium begins to enlarge – a proliferative phase at the level of the uterus. Accordingly, an analogue in the second half of the menstrual cycle of the progesterone phase of the ovary is the secretory phase of the endometrium, when the uterine glands roll up corkscrew-like and increase their secretion. In short, it is understood that the regulation of the menstrual cycle is a complex, descending and continuous process in which each higher unit releases bioactive substances that are needed to stimulate the lower unit in the neuroendocrine axis. In addition, the lower levels affect the activity of the upper ones: for example, the increased level of estrogens reduces the production of the pituitary hormone. This inextricable link between individual units is called feedback. In conclusion, the reproductive axis is a very subtle mechanism and as such it can easily be thrown out of balance by many and varied daily factors.