Anatomy and physiology of the female sexual system

  1. Gastroepato

  2. Clinical sexology

  3. Anatomy and fhysiology of the female sexual system

  4. Physiological anatomy of the female sexual system

  5. Uterus anatomy
     

notes by dott. Claudio Italiano

The sexual and reproductive function in women can be considered of two phases: the first one consisting in the preparation of the organism for conception and gestation, the second in the gestation itself. Approximately every 28 days the gonadotropic hormones of the adenohypophysis start the maturation of the new follicles in the ovary, one of which, at the end, ovulates on the 14th day of the cycle. During the maturation of follicles, estrogens are secreted. After ovulation, the secretory cells of the follicle are transformed into a corpus luteum that secretes considerable quantities of ovarian hormones, progesterone and estrogen. Two weeks later, the corpus luteum degenerates; then the ovarian hormones, progesterone and estrogens decrease strongly, and the menstruation intervenes: another ovarian cycle begins again.

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Ovulazione, FSH, LH, endometrio, ovulazione, estrogeni e progestiniciAfter a week or even more than a week of development - but before ovulation - one of the follicles begins to grow more than others. These others, on the other hand, begin to undergo involution (this process is called atresia) and become Atresic. We do not know what this atresia depends on, but the following has been hypothesized. The follicle that develops more than the others would secrete as much estrogen as to cause an inhibitory feedback on the hypophyseal secretion of FSH. The lack of this hormone would not hinder the further growth of the most developed follicle thanks to the stimulating action of the same estrogen. Instead all the other less developed and less estrogenic follicles, in the absence of FSH, would cease to grow and, in fact, regress. This process of atresia, of course, is important as it allows only one egg to mature enough until ovulation. In a woman whose sexual cycle is, as a rule, 28 days, ovulation occurs 14 days after the onset of menstruation. No one has witnessed the process of ovulation in women, but this process has been observed and studied experimentally in rats and rabbits. Shortly before ovulation, the external wall of the follicle, which protrudes to the surface of the ovary, swells rapidly and a small central area of ​​the capsule, the so-called stigma, becomes protruding like a nipple. Approximately in the next hour begins to drip liquid from the stigma. A couple of minutes later, as the follicle was reduced due to the leakage of liquid, the stigma breaks down and a more viscous liquid, the one that occupied the most central part of the follicle, is evacuated to the outside in the abdominal cavity. This viscous liquid contains the egg, surrounded by several layers of granulosa cells, which make up the so-called radiata corona, along with other layers of cells of the theca, loosely adhering.

Need for luteinizing hormone (LH) in vats of ovulation - Preovulatory discharge of LH.

For the final evolution of the follicle luteinizing hormone is needed. Without this hormone, even if there is an excess of FSH, ovulation does not take place. About two days before ovulation, for reasons not yet fully known, but will be explained later and in greater detail, the adenohypophyseal secretion of LH increases markedly, reaching - about 18 hours before ovulation - peaks 6 -10 times higher than previous levels. Also the secretion of FSH increases at the same time doubling approximately, and both hormones act synergistically causing a very rapid swelling of the follicle, just before ovulation. The LH also has a specific action on the cells of the theca and granulosa, transforming them into lutein cells that, in turn, secrete progesterone, but also estrogens in smaller quantities. Thus, the secretion of estrogen begins to decline approximately the day before ovulation, while small amounts of progesterone begin to be secreted.

It is in these conditions:

a) of very rapid follicle growth,
b) decreased estrogen secretion e
c) initiation of progesterone secretion that ovulation takes place.

All of this can not occur without the initial pre-ovulatory discharge of luteinizing hormone.

Ovulation mechanism

It is noted that the first motive is the abundant adenoipofisary secretion of luteinizing hormone. This hormone, in turn, promotes rapid secretion of follicular steroid hormones, originally containing a small amount of progesterone. Within two hours, two events occur: 1) The external case (the follicle capsule) begins to produce proteolytic enzymes; these dissolve the ca-psygeal wall, thinning it and allowing a further swelling of the entire follicle, as well as the degeneration of the stigma. 2) The luteinization process of the cells of the case and of the granulosa is accompanied by the neoformation of blood vessels in the follicle wall. This, in turn, causes a plasma transudation into the follicle, which is further re-inflated. In the end, the follicle swelling, together with the simultaneous degeneration of the stigma, causes the follicle to break with the egg evagination.

The lutein phase luteinic body of the ovarian cycle

In the first hours, after the expulsion of the egg from the follicle, the remaining cells of the theca undergo rapid physical and chemical transformation, a process that is defined as luteinization, which leads to the formation of the corpus luteum, which secretes the hormones progesterone and estrogen. That is, these cells are greatly enlarged and form lipid inclusions which give the cells a yellowish color, hence the term luteum. In this mass of developing lutein cells there is a dense vascular network of spraying. In the woman, normally, the corpus luteum is enlarged up to about 1.5 cm, reaching this stage of development towards the seventh or the eighth day after ovulation. After that, it begins to regress and around the 12th day it loses its secretory function, together with its lipid characteristics, transforming itself into the so-called corpus albicans; finally, after a few weeks it is replaced by connective tissue. Luteinizing function of luteinizing hormone (LH). The transformation of granulosa cells into lutein cells depends entirely on the secretion of LH by the adenohypophysis. In fact it is to this function that the LH owes its name. Purification of the corpus luteum: function of Luteinizing hormone LH. The corpus luteum is an organ with a strong secretory activity, secreting significant quantities of both progesterone and estrogen. Once the LH (especially the secretion during the ovulatory wave) has acted on the cells of the casket and granulosa to give rise to luteinization, the newly formed lutein cells seem to be programmed to meet a preordained set a) of proliferation, b) of enlargement, c) of secretion and, finally, d) of degeneration. This process evolves even if there is no further pituitary secretion of LH. However, in the presence of LH, the development of the corpus luteum is exalted, its secretion is increased and its prolonged life. During this phase of the ovarian cycle the concentration of LH is very low; however, in the absence of this LH, the persistence of the corpus luteum is limited on average only to 6-8 days, instead of 12, as usual. You will see in the next chapter, about pregnancy, that there is another hormone, the chorionic gonadotropin, which has exactly the same properties as the luteinizing hormone. The chorionic gonadotropin is secreted by the placenta and can act on the corpus luteum, prolonging its life, practically, for the entire duration of pregnancy. End of an ovarian cycle and beginning of the next one. During the luteinic phase of the ovarian cycle, the large amount of estrogen (and perhaps even, to a very small extent, progesterone) secreted by the corpus luteum determines an inhibitory feedback for which the secretion of FSH and LH decreases. Therefore, during this period, no other follicles develop in the ovary. However, when the corpus luteum degenerates completely, after the 12 days of persistence around the 26th day of the sexual cycle), seeing the lack of inhibitory feedback, the anterior pituitary can now secrete considerable amounts of FSH and also increase moderately the secretion of LH. These hormones start the development of new follicles and start another ovarian cycle. At the same time, the poor secretion of progesterone and estrogen causes menstruation to occur.

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