The menstrual cycle is the set of physiological phenomena of women preparing the body for a possible fertilization and occurs most often on a periodic basis.
The most visible of these changes is menstruation. The menstrual cycle begins at puberty and ends at menopause by depletion of ovarian follicles and by increasing resistance of ovarian follicles to the action of gonadotropin.
This cycle is often 28 days under our latitudes, but this figure is only a convenient average (28 days = 4 weeks) and represents neither average nor the method of distribution in the world. Two independent investigations as it gives 32 days in India. It is controlled by hormones.
The bleeding appears to stop contraception oestro progestin (classical pill) have no relation to menstruation physiological and is bleeding genital a sharp decline in the rate of hormones in the blood. This phenomenon is known as bleeding deprivation.
Knowledge of the menstrual cycle can be used for contraceptive purposes, provided to employ a rigorous method of Natural Family Planning. Knowledge of the menstrual cycle is important to approach the study of disorders of menstruation, in the exploration of infertility and in the implementation of technical medical assisted procreation.
Some neurons have a specific function since endocrine release a hormone, gonadotropin-releasing hormone, or GnRH (Gonadotropin Releasing Hormone), a pulsatile, in the vascular system door hypothalamic-pituitary, unlike conventional neurons that release of neurotransmitters at synapses; GnRH causes the pituitary secretion (by glandular cells of the anterior) two gonadotropes or gonadotropin hormones, FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone); changes in the plasma levels of these hormones during the cycle define the pituitary hormone cycle.
* The FSH, follicle-stimulating hormone, is essential to the development of follicles gamétogènes and ensures the maturation of a follicle cycle, the follicle de Graaf, on the other hand it determines, with LH, installing the function endocrine follicles at préantral.
* The discharge plasma a strong dose of FSH and LH especially triggers ovulation, which takes place 36 hours after the beginning of the peak ovulatory.
* LH, luteinizing hormone, allows the formation of the corpus luteum at the 2nd phase of the cycle and is responsible for cell transformation of cells in the granulosa cells in large luteal (luteinization) source of progesterone.
The ovarian cycle includes the resumption of oogenesis (oocyte I 2n chromosomes is blocked during prophase of the 1st meiosis since fetal life), hormonal secretions ovarian essential to ovulation, the changes to the uterine fertilization and the preparation of the endometrium for implantation.
The exocrine and endocrine functioning of the ovary as a support anatomical the ovarian follicle, which also varies so cyclical.
There are therefore three cycles in the ovary:
* The cycle follicular
* The cycle exocrine corresponding to the resumption of oogenesis
* The cycle endocrine
The follicles are contained in the stroma cortical. There are two types of follicles:
* The evolving follicles or gamétogènes which one cycle reach maturity (follicle de Graaf) pondra and an egg follicles involutifs which dégénèreront.
* There are different types of follicles corresponding to the evolving stages of progressive maturation of the same morphological structure, they are chronologically
o The primordial follicle
o The primary follicle
o The secondary follicle
o The tertiary follicle (préantral then cavitary)
o The follicle or mature follicle de Graaf
Each follicle contains a first-oocyte or egg I (2n chromosomes) blocked during prophase of the 1st meiosis (diplotène or diacynèse)
The primordial follicle is very small, 40 to 50 micrometers and is formed by a thin shell containing the oocyte I; kernel oocyte has a large aspect quiescent (chromosomes are dispersed in a fine chromatin) and has 1 or 2 nucleoli ; Hull follicular consists of a single layer of flattened epithelial cells, the cells folliculeuses, surrounded by a thick basal membrane, the membrane Slavjanski.
* The cells of the internal théque under the action of LH syntéthisent androgens (steroids to 19 carbon atoms). These androgens are converted into estrogen (steroids to 18 carbon atoms) by the action of an aromatase synthesized by the follicle cells under the effect of FSH.
* Follicular cells also secrete a polypeptide hormone, inhibin, which exerts a negative feedback on the secretion of FSH particularly in the second half of the pre-ovulatory phase, which would be one of the causes of the decline of follicles.
* The dominant follicle, more rich in receivers FSH, so sensitive to low plasma levels of this hormone, is the only one to continue his maturation and become the follicle De Graaf
* When estradiol remains at a certain rate for 48 hours, there is a positive feedback on the secretion of LH triggering the LH surge.
* This peak LH or discharge ovulante, is the direct supervisor of ovulation
The fallopian tube has a quadruple role in reproduction:
* The flag ensures capture of the egg, it surrounds the ovary of its many fringe mobile, enserre more or less at the time of ovulation and the egg gets laid eggs; capture of an egg by mistake is facilitated by the existence of a current serous home peritoneal guide the egg to the opening flag (ostium abdominal); this sérosité then returned into the peritoneal cavity by the slots lymph mucosa tubal
* The egg reaches the bulb in a few hours, but its level is achieved fertilization, the fertilized egg is named egg or zygote.