menstrual cycle and hormonal regulation

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I- MENSTRUAL CYCLE :

A- DEFINITION :

Throughout the active genital life, l’histological appearance of the surface layer "functional" of’endometrial varies from day to day according to a regular cycle : periods. The cycle lasts 28 days but can vary, it begins at puberty to 12-15 years and continues throughout reproductive life of women.

The menstrual cycle is the sequence of a set of physiological phenomena regularly repeating outside the periods of pregnancy, from puberty to menopause, the start of a menstrual period at the beginning of the following for an average of 28 days. it s’is :

  1. d’a physiological phenomenon characterized by a periodic blood flow of uterine origin, occurring in women when there was no fertilization, from puberty to menopause.
  2. d’a physiological phenomenon which corresponds to the peeling of the surface layer of the endometrium due to local vascular phenomena associated with the cessation of operation of the corpus luteum.

B- PHASES OF MENSTRUAL CYCLE :

The menstrual cycle is characterized by 3 cyclic phases which follow one another continuously.

1- Phase proliférative (estrogenic or follicular) :

  • Occurs between 6th and the 14th day of the cycle and coincides with the proliferation of ovarian follicles
  • The flaky layer "functional layer" over the rules regenerates from the basal layer, there will be progressive thickening of the uterine lining.
  • The glandular tubes, which were rare, become many.
  • The vascularization of’endometrium increases, arteries grow, arterioles of the functional layer (terminal arterioles) s’longer and start to become crooked.
  • L’epithelium reappears.

2- secretory phase (estrogen-progestin or luteal follicle iutéinique) :

  • after ovulation, l’endometrium undergoes considerable thickening (6mm). The glandular proliferation reached its maximum’intensity: glandular tubes, numerous, become convoluted and sinuous, their width and also increases their light expands irregularly: l’the womb will’aspect of "uterine lace" favoring implantation.
  • Glandular cells show signs of secretion: glycogen.
  • Two cell layers will s’individualize :

a surface layer "compact" poor glands,
a deep layer "spongy" rich in glands.

  • Arterioles undergo winding on themselves and become: spiral arterioles.

From the 24erne cycle day, arterioles still spiralisent causing circulatory slowdown and congestion of the uterine lining which characterizes the ischemic phase to the end of the cycle : circulatory slowdown causes superficial necrosis and rupture of the spiral arterioles.

3- Phase menstruelle :

The breaking of the spiral arteries causes’haemorrhage.

Small hemorrhages occur in the territory of each artery, in the form of small local hematoma 0.5 2 mm diameter, each hematoma bleeding during 90 So the minute’menstrual bleeding is a long process and takes several days.

The glands of the functional layer in necro-ulcerative stage, are then removed by fragment, deep areas stand to 4th or 5th day, to’exception of the basal layer, alone, persists. At the same time, l’endometrium begins to regenerate by re-epithelialization of the surface of the basal layer and continuing the cycle resumes.

C- MENSTRUAL CYCLE DISORDERS :

Some women experiencing cycles shorter or longer than 28 days. These variations in length occur during the follicular phase, since ovulation has always held the 14th day before the first day of menstruation, regardless of the cycle. Before 40 years, anarchy cycles can be the consequence of a hormonal imbalance or malfunction of the thyroid. Some women may have anovulatory cycles, c’is to say without ovulation. Past 40 years, l’irregular cycles is the sign of’entry of women in the peri-menopausal stage. The disappearance of the rules can also s’observed in some women. This is often the case in very thin women, suffering’anorexia or to very restrictive diets that aim to remove lipids.

Figure 23. ovarian and uterine cycle Cycle
Figure 24. Menstrual cycle

II- HORMONE REGULATION :

A- HORMONAL CONTROL :

L’Sexual activity is controlled by hormonal factors and s’carries on 3 levels

– At the’hypothalamus :

L’hypothalamus, territory of reduced’brain, control pituitary hormone secretion through hypothalamic neurohormones : GnRH = gonadocaval Releasing-hormon ou gonadocaval libérine.

– At the’hypophyse :

L’pituitary is’joining of 2 parties : l’The adenohypophysis and neurohypophysis. L’adenohypophysis or anterior pituitary or adenohypophysis involved in the control of’ovary. Stimulated by’hypothalamus secretes GnRH, l’anterior pituitary develops pituitary hormones that are released into the blood and act on’ovary. These hormones are called gonadotropins or gonadotropin and among these:

La FSH : Folliculo-stimuline or hormone-folliculo stimulante.
La LH : Luteal-stimulating hormone or luteinizing hormone.

– At the’ovary :

Stimulated by FSH and LH, endocrine cells of’developing ovarian steroid hormones from cholesterol among these hormones :

estrogens (17 B oestradiol).
progesterone.

B- HORMONE REGULATION :

The hormonal regulation in women s’carried out as follows : L’adenohypophysis, stimulated by GnRH releases FSH and LH.

FSH and LH cause changes on’ovary, who go, in turn, produce estrogen and progesterone.

Figure 25. Diagram of neuro-pituitary-ovarian regulation

1- During Phase preovulatory foliiculo-estrogen :

L’anterior pituitary secretes FSH will stimulate follicular development : proliferation of granulosa cells with development of the zona pellucida.

L’anterior pituitary begins to secrete the progressively increasing amount LH and end of follicular maturation stages, LH will stimulate differentiation of cells of the theca interna, which will in turn secrete estrogen. FSH and LH work synergistically : or FSH or LH acting isolation, can cause follicular growth.

2- By the middle of the cycle : ovulation

The gonadotropins cause dissociation of cumulus oophorus cells, the resumption of the first meiotic division which s’ends in a few hours. Thirty six hours after the peak, l’II oocyte is released. L’ovulation is due to mid-cyclic discharge of LH and FSH or discharge gonadotropic [peak pituitary LH and FSH]

3- During the post-ovulatory luteal phase :

after ovulation, the follicle remnants change under the’influence of l.h (that continues to be secreted by’hypophyse) in an endocrine structure : the corpus luteum begins to secrete progesterone and especially the little’estrogen.

C- CYCLIC CHANGES :

For pituitary hormones : FSH and LH have a variable rate over the cycle :
– FSH is high at the beginning of the cycle and has a peak preovulatory midcycle.
– LH has a low rate throughout the cycle and also a peak preovulatory important midcycle.

For ovarian hormones:
– estrogen, low early in the cycle, their rate s’student and there is a significant spike 12 at 24 hours before’ovulation. In luteal phase, there is an increase in estrogen followed’decreased during menstruation.
– Progesterone rate varies during menstrual cycle : it is very low throughout the pre-ovulatory phase, s’student after’ovulation up’at 8th day luteal phase, then declines, up’to menstruation.

Figure 26. Hormonal Change during the cyle

D- ROLES OF OVARIAN HORMONES :

These steroid sex hormones determine the’appearance of primary sexual characteristics in fetuses, l’appearance of secondary sexual characteristics at puberty and control the’ovogenèse.

1- estrogen :

  • Have an influence on cyclic variations of’epithelium of the fallopian tube, of the’endometrial : proliferation of endometrial glands, reconstruction of the endometrium.
  • Stimulate contractions of the myometrium.
  • Make the cervical mucus is abundant at fertilization.

2- progesterone :

  • Prepares the uterine lining for implantation : growth of glands and secretion.
  • Inhibits contractions of the myometrium.
  • amends’abundance of mucus.

THERE is a "synergy’action "between estrogen and progesterone: l’action of progesterone can not s’exercised on a prepared endometrium by estrogen.

S’No it is not fertilizations, to the 24th cycle day, the corpus luteum s’atrophy, production’estrogen and progesterone ceases abruptly and the endometrial lining sheds : these are the rules.

And, on the other hand, there fertilization, the corpus luteum persists and with it, the presence’high levels of progesterone : rate that will be maintained until’at an advanced stage of pregnancy, the embryo develops a hormone the’HCG (gonadotrophine chorionique ) which ensures the survival of the corpus luteum. The corpus luteum is a gestational corpus luteum and continues to secrete during 6 estrogen and progesterone weeks, will be taken over by the placenta (pregnancy test based on the presence of’HCG detectable in the urine of pregnant women .L’HCG modifies the immune response of’uterus overlooked embryo : l’uterus behaves as if the embryo n’was not a foreign body.

E- RÉTROCONTRÔLES :

1- Ovarian hormones act back on’hypophyse : Feed-back.

1- At the beginning of the cycle :

Just before’ovulation, FSH triggers follicle maturation and secretion’estrogen. When lethal d’Estrogen comes at a high level it inhibits the production of F. S. H : Feed back négatif.

2- A l’ovulation :

A peak’estrogen triggers a surge of LH and FSH causing the’ovulation : Feed back positif.

3- after ovulation :

It was the luteum formation and secretion of increasing amounts of progesterone and’estrogen. When the estrogen plus progestin increases rates, it triggers a negative feed back on FSH and LH

The braking of the secretion of FSH and LH causes the regression of the corpus luteum which results in that the rate of ovarian hormones reaches its lowest value ; c’is menstruating.

Because of’collapse rate of ovarian hormones, FSH and LH secretion wakes up and the cycle resumes.

2- The woman with tumor of’this pituitary gland, among the many disorders, l’lack of rules. L’pituitary acts on a woman's menstrual cycle.

In women whose infertility is due to’lack of’ovulation, FSH and LH injections often recover fertility. L’pituitary acts on’ovary FSH and LH.

In women whose infertility is due to’lack of’ovulation, l’Injection rhythms and proper doses of GnRH often restores’ovulation. L’hypothalamus controls the’activity of’ovary GnRH which determines’activity of’hypophyse.

In postmenopausal women, there is a significant increase in FSH and LH. L’ovary has feedback on’hypophyse.

L’injection’a precise dose’estradiol in a mouse quickly produced a slight decrease in FSH levels in the blood followed’a massive increase in LH levels. L’estradiol exerts a negative feedback on FSH secretion and a positive feedback on the LH.

F- DEFINITIONS :

– Gonadolibérine. Gn-RH (gonadotropin-releasing hormone): Decapeptide synthesized by’hypothalamus, acting on’pituitary to the synthesis and release of gonadotropins.

– Gonadotrophine (you gr. gone « seed », -trophy and suff. other). Syn. gonadostimuline, hormone gonadotrope. General term for a group’protein hormones equipped with’a stimulating activity on the genital glands (ovaries or testis). There are two main groups: the pituitary gonadotropins (FSH, LH and prolactin), and chorionic gonadotropin.

– FSH (Eng., abrév. to follicle stimulating hormone). Syn. hormone folliculostimulante, follitropine. Glycoprotein hormone of molecular weight 31 000 daltons, secreted by the cells of gonadotropin’anterior pituitary. FSH is, like LH and’hCG, consists of two polypeptide chains, alpha and beta. The alpha chain is common to all three hormones, while the beta chain gives each of’They its biological and immunological specificity. FSH secretion is cyclic in women, but present in both follicular and luteal phases of the menstrual cycle; it stimulates the maturation and function of granulosa cells. FSH secretion is stimulated by GnRH, modulated by sex steroids, depressed by’inhibine.

– LH (Eng., abrév. luteinizing hormone for). Syn. luteinizing hormone : Glycoprotein hormone of molecular weight 29 000 daltons, secreted by the cells of gonadotropin’anterior pituitary. LH secretion is cyclic in women, with an increase in late follicular phase, a preovulatory followed by a decrease in luteal phase. LH acts on many gonadal cells, by promoting the synthesis of sex steroids; in women it occurs in a privileged way in’ovulation. LH secretion is stimulated by GnRH

– steroid hormone. Syn. steroid hormones. hormonal substances derived group sterols, which are formed from cholesterol, and isolated from endocrine glands (corticosurrénale, ovary).

– estrogen (of estrus, and -Gene). Syn. estrogens. hormonal steroid group having a carbon skeleton 18 carbon atoms and ring A carrier Aromatic’phenolic function 3. Natural estrogens are synthesized in women

iss in ovarian follicles, in the corpus luteum, L’physiological action of estrogen s’exerts on the genital tract and female sexual characteristics at puberty.

– Inhibine : water-soluble protein, non-steroid, d’origine gonadique, secreted in’ovary by granulosa cells: This secretion is stimulated by FSH. For feedback, l’inhibin inhibits the production of FSH.

– progesterone (pro-, years. wear « porter », and suff. d’hormone). Steroid hormone of the group consisting of a pregnane nucleus 21 carbon atoms. Hormone mainly from the corpus luteum’ovary.

Course Dr A HECINI – Faculty of Constantine