Physiological anatomy of the female sexual system

  1. Gastroepato
  2. Clinical sexology

notes by dr 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.

Physiology of female reproduction


The female reproductive system includes the ovary, the fallopian tubes, the uterus and the vagina. The reproductive process begins with the development of follicles in the ovary. At the middle of every monthly sexual ode, only one egg is usually expelled from an ovarian follicle in the abdominal cavity. This egg then passes through one of the Falloppio trumpets descending into the uterus and, if it has been fertilized by a sperm, it implants into the uterus where it gives rise to the fetus, to the placenta and to the fetal membranes. During fetal life, the outer surface of the ovary is covered by a germinative epithelium, which embryologically derives directly from the epithelium of the germinative ridges. When developing the fetus, the primordial eggs differ from the germinative epithelium and migrate in the thickness of the cortical of the ovary, dragging behind a layer of epithelioid granulosa cells. The egg surrounded by a single layer of epithelioid granulosa cells, is what is called a primordial follicle. At birth there are about 750,000 primary follicles in both ovaries, but this number is rapidly reduced, so that only 400,000 remain at puberty. During the fertile age of the woman only about 450 of these follicles mature enough to expel their egg, while the rest degenerate (become Atresic). At the end of the fertile period, at the menopause, only a few primordial follicles remain in the ovary, which are also destined to degenerate soon after.Risultati immagini per uterus

The female hormonal system

The female hormonal system, like the male one, consists of three different hierarchies of big man:
1. The liberating factors of the hypothalamus, the liberating factor of the follicle-stimulating hormone (FRF) and the liberating factor of the luteinizing hormone (LRF) (which could be the same factor).
2 Adenohypophysis hormones, follicle-stimulating hormone (FSH) and luteinizing hormone LH
secreted in response to the factor, or factors, of the hypothalamus.
3. Ovarian hormones, estrogen and progesterone, secreted ovary in response to adenohypophyseal hormones.
The various hormones are not secreted in a constant and continuous way, but rather at drastically variable rhythms during the different phases of the woman's cycle. Although no detailed measurements have been made, it is reasonable to assume that hypothalamic liberating factors also undergo cyclical variations.
Before discussing the connections between these different hormones, it is convenient to describe the correlations in relation to the ovarian function.

Monthly ovarian cycle and function of gonadotropic hormones

The normal fertile life of the woman is characterized by monthly rhythmic variations related to the secretion of female sex hormones and the corresponding changes in the sexual organs themselves. This rhythmic picture is what is defined as a woman's sexual cycle (or menstrual cycle). Each cycle lasts an average of 28 days. This duration may be reduced to 20 days, or move up to 45 days even in completely normal women, although an abnormal duration of the cycle is often accompanied by a decrease in fertility.
The two most significant events of the female sexual cycle are: first, that at each cycle only one mature egg is released from the ovaries, so that only one fetus can begin to develop at a time; second, that the uterine endometrium is prepared at the right time of the cycle for implantation of the fertilized egg.
Gonadotropic hormones. The sexual cycle depends entirely on the gonadotropic hormones secreted by the anterior pituitary. The ovaries, if not stimulated by the gonadotropic hormones, remain completely inactive, something that usually occurs during childhood, when gonadotropic hormones are almost not secreted. But at the age of about eight years, the pituitary begins to secrete increasing quantities of gonadotropic hormones and this culminates with the beginning of the monthly sex cycles, at an age between eleven and fifteen. This is the so-called period of puberty.

The anterior pituitary secretes two different hormones, notoriously essential for a full function of the ovaries:

1) the follìcolo-stimulating hormone (FSH),
2) luteinizing hormone (LH).

Both of these hormones are low molecular weight glycoproteins of 30,000 and 26,000, respectively. LH in the male is also called interstitial cell stimulating hormone (ICSH), as it stimulates the activity of these cells.
In every month of the woman's sexual cycle, there is a cyclical increase and decrease of FSH and LH. These cyclic variations, in turn, determine the ovaries cyclical changes, which will be described later.
Both FSH and LH stimulate ovarian cells by combining with specific receptors of cell membranes, which in turn activate adenyl cyclase. This increases cyclic AMP in cells, leading to the development and secretion of special ovarian cells. So the mechanism of action of these hormones resembles the usual cyclic AMP system for hormone control.

Maturing of the follicle
FSH hormone

During childhood, primordial follicles do not ripen at all but, at puberty, when FSH begins to be secreted in large quantities, the ovaries in full and especially the follicles inside are beginning to develop. The first stage of follicular development is represented by an enlargement of the egg itself, followed by a proliferation of the granulosa cells and the development of cell layers of the theca, all around the surface of the granulosa cells. The cells of the theca originate from the ovary stroma and soon take on epithelioid characteristics. Taken together, these cells constitute the so-called inner casing. It is mainly these cells that secrete most of the female hormones, estrogens and progesterone. A capsule of connective tissue forms around the inner case. This is called an external casing and forms the capsule of the evolving follicle. The vesicular follicles. At the beginning of each woman's monthly sex cycle, almost at the beginning of menstruation, the concentrations of FSH and LH are increased. These increases accelerate the development of the granulosa cells and the case of about twenty ovarian follicles every month. The cells of the casket and granulosa secrete a follicular fluid, rich in estrogens, one of the important female sex hormones, which will be explained later. The accumulation of this liquid in the follicle causes the appearance of an antrum in the mass of the cells of the case and of the granular. After the formation of the antrum, the cells of the theca and granulosa continue to proliferate, the secretion is accelerated, and each evolving follicle is transformed into the so-called vesicular follicle. This faster growth and more abundant secretion is determined not only by the follicle-stimulating hormone, but also by two other factors. First, a small basal amount of luteinizing hormone is secreted by the anterior pituitary; this hormone has a synergistic and reinforcing effect compared to the stimulating action of FSH. Secondly, the estrogen secreted in the follicle also has a similar synergistic effect. As the vesicular follicle grows, the cells of the case and those of the granulosa continue to develop at one of the follicle's poles. The egg is housed in this cellular mass (cumulus oophorus).


> segue fisiologia femminile 2