Mutual influence of the hypothalamic-pituitary-ovarian axis
If peak LH levels are not sufficiently large, ovulation will not occur and is called an anovulatory cycle. The phases of the urogenital cycle continue, but the failure to ovulate prevents the corpus luteum from developing.
Now, after much discussion about the known information about the interactions between the components of the female hormone system, we can participate in explaining the interaction that controls the rhythm of the cycle. menstrual period.
1. Post-ovulatory ovarian hormone secretion, and a decrease in gonadal regulatory hormone from the pituitary gland. During the period after ovulation and the onset of menstruation, the corpus luteum secretes large amounts of oestrogen and progesterone, as well as inhibin. These hormones work together to produce a negative feedback on the anterior pituitary and hypothalamus, reducing the secretion of FSH and LH and causing FSH and LH levels to reach their lowest level about 3-4 days before the onset of menstruation.
2. Follicular phase of development: 2-3 days before menstruation, the corpus luteum almost completely contracts, and the secretion of oestrogen, progesterone, and inhibin by the corpus luteum drops to very low levels.
This causes the hypothalamus and pituitary gland to be released from the negative feedback produced by these hormones. Thus, after 1 day onward, at the onset of menstruation, the pituitary secretion of FSH is doubled, and then, for several days after the onset of menstruation, the secretion of LH is also slightly increased. These two hormones initiate the growth of new follicles and accelerate the secretion of oestrogen, peaking in oestrogen levels about 12.5 -13 days after the start of a menstrual cycle. During the first 11-12 days of follicular development, the pituitary gland's level of secretion of the gonadal regulatory hormones FSH and LH is slightly reduced due to the negative feedback effect of predominantly oestrogen on the anterior lobe. Pituitary. Then there is the time when LH increases suddenly and FSH also increases but less. This produces peaks of LH and FSH, which then lead to ovulation.
3. LH and FSH peaks induce ovulation: At about 11.5-12 days after the start of CKN, the decrease in FSH and LH secretion stops abruptly. It is thought that the high levels of oestrogen at that time (or due to the emergence of progesterone secretion from the follicle) induce positive feedback on the anterior pituitary gland (explained in the previous section), creating a very high LH peak, and a lower FSH peak. Whatever causes LH and FSH peaks during pre-ovulation, very high levels of LH lead to two events: ovulation and subsequent development and secretion of the corpus luteum.
In addition, the sex hormone system begins a new secretory phase until the next ovulation.
Non-ovulatory cycle - sexual cycle during puberty
If peak LH levels are not sufficiently large, ovulation will not occur, and is referred to as a “non-ovulatory cycle.” The phases of the urogenital cycle continue, but they change in the following direction: First, the absence of ovulation causes the corpus luteum to fail to develop, and there is almost no progesterone secretion during the later part of the pregnancy. menstrual cycle. Second, the cycle will shorten by a few days, but the pace will still be maintained. Therefore, progesterone does not appear to be necessary in maintaining rhythm, although it may alter the rhythm of the cycle.