Hormonal changes in a cycle

From the adolescence until menopause, a woman’s body undergoes constant cyclical changes. Each woman has her biological clock ticking and measuring time from one menstrual cycle to another. The clock is regulated by the endocrine, working on the basis of feedback. The system contains:

• Hypothalamus
• Anterior lobe of the pituitary gland
• Ovaries

The Hypothalamus has the role of the governing body and guardian. It is sensitive to both the external information, such as light, stress, mood, as well as the internal one as it react to hormones secreted by the ovaries. Thanks to this coordination, the hypothalamus affects the pituitary gland’s work by sending out neurohormone signals (GnRH), stimulating or restraining the production of hormones by the pituitary gland.

At the beginning of the cycle, starting from the first day of menstrual bleeding, we have low levels of ovary hormones. The pituitary gland, stimulated by the hypothalamus, emits the stimulating hormone (FSH). At this signal one of the follicles (with the hidden ovary cell) starts to mature in one of the ovaries. The follicle is the gland of the internal secretion - secreting hormones called estrogen. Estrogen through the circulatory system affects the woman’s body, also reaching the hypothalamus and pituitary gland.

The high lever of estrogen stimulates eruption of accumulated luteinizing hormone (LH) which is responsible for the release of the mature ovary cell i.e. ovulation triggering.

Under the influence of LH in the place of a broken follicle a transitional gland comes into being, the so-called corpus luteum.

The corpus luteum produces progesterone, a hormone which prevents other ovary cells to grow, and through information sending to the Hypothalamus the secretion of the pituitary gland’s hormones. The corpus luteum extinguishes after around 2 weeks and turns into atretic corpus luteum. The level of progesterone falls and that is a signal for hypothalamus to begin a new cycle.