Introduction

The ovaries are experiencing pelvic ovoid + / - covered by the flag of the tube. The surface of the ovary is covered by a simple cuboidal epithelium and in this epithelium is a connective tissue called "stroma" The stroma is composed of several parts: - a region responsible for the whitish ovaries => albuginea - a cortical area or cortex which contains the ovarian follicles maturing and are the site of folliculogenesis. - A medulla rich loose connective tissue containing blood vessels, lymph vessels and nerves.

I. Oogenesis and folliculogenesis.

The development of gametes in oogenesis occurs within ovarian follicles in a phase of multiplication, growth and maturation phase. And folliculogenesis and oogenesis are related, they provide a cyclical production of female gametes.

​​I.1) Phase multiplication

By the third week of intrauterine development (UI), stem cells appear to gametes are migrating primordial germ cells in the gonad and future at the end of the second month of life they give rise to IU oogonia. The oogonia are diploid cells (46 chr.) That multiply successively in waves of mitoses. In the seventh month of life IU, a non-renewable stock of several million oogonia leave the mitotic cycle and turns into oocyte I. In the ovary, oocytes are surrounded by follicular cells I flattened where they establish active interactions. These adherens junctions and junctions permeable and together form the primordial follicle. The first primordial follicles appear at the end of the third month of life UI.

​​I.2) the maturation phase

Oocyte maturation begins at the same time I appear the oocytes, the oocyte I under the influence of a factor inducing meiosis begins meiosis I. Oocytes replicate their DNA and then I come in prophase of first division méitotique. Meiosis I is blocked in the prophase I diplotene. -> It's also the time when I isolate the oocytes in the primordial follicle. Blocking meiosis I persists until ovulation.

This block is dependent on the meiosis inhibitory factor, or IMO, the IMO is localized in the granulosa cells and the long phase locking is also characterized by significant growth in the volume of the oocyte. Indeed during diplotene, the chromosomes décondensent to ensure a synthesis of mRNA and rRNA. Thus large amounts of RNA are stored in the oocyte cytoplasm, small amounts of RNA is used by the oocyte and the rest will be the subject of the future zygote during the first division of segmentation. Between the membrane of the follicle and ovarian stroma is set up a basal lamina called "membrane Slavjanski".

This membrane separates the oocyte and the follicle. The primordial follicles occupy the ovarian cortex. Most ovarian follicles degenerate during fetal life and the loss of follicles continues until puberty. And the sixth month of fetal life, the stock of primordial follicles is 6 million for the two ovaries and passes 2 million at the time of birth and a few hundred thousand at the time of puberty.

At puberty the development of the activity of the hypothalamic-pituitary axis allows the growth of ovarian follicles and the resumption of meiosis. The egg-cells foliculaires interractions are essential to the achievement of these steps. Indeed in the follicle, the oocyte induces mitotic follicular cell thanks to factors and follicle cells stimulated by FSH synthesize steroid hormones and growth factors necessary for oocyte maturation and the development of follicles.

Depending on the size and maturation of the follicle can be distinguished:
-> Primary follicles
-> = The growing follicles Antral follicles pre-
-> = The follicles mature antral follicle
-> De Graaf follicles

Follicular growth is a regular phenomenon and cyclical which manages the capital of the oocytes formed during life. It is characterized by the recruitment and selection of ovarian follicles of up to ovulation. Recruiting key pre-antral follicles in waves leaving the pool of growing follicles. The number of follicles recruited varies with age. Recruitment induced by FSH occurs at least 3 cycles before ovulation.

All recruited follicles are potentially able to ovulate, however only one, the largest mature => ovulatory follicles or dominant follicle is selected. This selection is a phenomenon induced by a hormone-dependent secretion of FSH. Indeed, the estrogen produced during follicular growth slow by a negative feedback effect of the synthesis of FSH. The other follicles regress selected because of the lack of FSH stimulation, the regression is characterized by the entry into apoptosis of granulosa cells.

At menopause the ovaries become quiescent contain only remnants of follicles.

II. The follicles.

​​II.1) The primary follicle.

Are composed of a layer of follicle cells surrounding the oocyte cubic, it is isolated from the ovarian stroma by the membrane Slavjanski. At this stage, the follicle is devoid of hormonal sensors, it is under the control of EGF. I

​​I.2) Pre-Antral follicle.

The development of the follicle is marked by the growth of follicular cells. The cubic cells become large, they take the name of granule cells. They are organized to form several layers around the oocyte and granulosa this is. The granulosa cells establish gap junctions between them and the oocytes. These junctions allow the passage of small molecules in the oocyte. The granulosa is not vascularized, in granulosa sensors appear to FSH. Once the follicles become responsive to stimulation anterior pituitary gonadotropin. Between the plasma membrane and granulosa cells a fibrillar zone consists of three sulfated glycoproteins ZP1 ZP2 and ZP3 secreted by the oocyte is taking place. It characterizes the zona pellucida. This area meets the junctions established between the granulosa cells and oocyte. At the periphery of the membrane Slavjanski, ovarian stromal cells are differentiated, this transformation leads to the establishment of internal and external libraries. The theca externa is a little vascularized fibrous connective tissue. The theca interna cell tissue is highly vascularized, the theca interna cells communicate with each other by gap junctions and these cells are set up sensors to LH.

​​II.3) the antral follicles.

Secretion of follicle cells create small cavities in the granulosa cell mass. The merging of small cavities is a single cavity => antrum. The formation of the antrum has the effect of pushing the granulosa of the follicle at the periphery against the theca interna. The mass of granular cells surrounding the oocyte side which projects into the cavity is called antral cumulus oophorus.

​​II.4) the Graafian follicle

The changes that mark the transition from stage to stage of antral follicle Graafian follicle occur in the hours before ovulation. In the hours preceding ovulation, the cumulus cells are transformed, those immediately surrounding the oocyte are arranged radially to form the oocyte and the corona radiata (see photo 6).

Cumulus cells are separated so that they form a mass with a nebulous appearance. At this stage, the intercellular contacts through the zona pellucida has completely disappeared. It is the discharge, or gonadotrope pituitary LH surge that causes the breakdown of the junctions between the granulosa and cumulus and close the inhibitory effect of the granulosa. The LH surge also allows the resumption of meiosis and oocyte maturation by activation of I MPF. At this stage form of cortical granules that form within the Golgi vesicles, they migrate under the plasma membrane of the oocyte. The completion of meiosis I results in the formation of the oocyte II and first polar body.

The oocyte II has inherited almost all the cytoplasm when the first polar body has only a minimal amount of cytoplasm. The oocyte II undertakes immediately in the second meiotic division, but meiosis is blocked in metaphase II under the effect of oocyte cytoplasmic factor CSF.

Meiosis II is completed only if fertilization, the egg degenerates if not complete its meiosis.

III.L ovulation

Just after ovulation, the oocyte and surrounding cells detach directly from the follicle wall and floats in the follicular fluid. The appearance of the stigma on the surface of the ovary indicates the Eminent ovulation. Stigma => Area prominence of mature follicles in the ovarian epithelium. This area appears transparent. Ovulation can rupture of the follicle and expulsion of a fertilized oocyte II, it takes place in the middle of the menstrual cycle to day 14. The agent triggering ovulation is the peak of luteinizing hormone => LH surge that causes the secretion of prostaglandin by the granulosa. Prostaglandins are responsible for a decrease in local blood flow, causing the death of epithelial cells at the ovarian stigma. Meanwhile prostaglandins activate a plasmin, plasmin activated allows the disintegration of the wall of the Graafian follicle. Rupture of the follicle associated with the hydrostatic pressure drop causes contraction of the follicle and the ejection pressure in the peritoneal cavity of follicular fluid and oocyte II surrounded by the corona radiata and cumulus oophorus. At the time of ovulation, the pavilion of the tube just cover the area of ​​stigma, as soon as the egg is expelled from the contractile activity of smooth muscle cells in the wall of the tube, associated with the activity of hair cells will push the egg into the tubal lumen. After ovulation, the oocyte and the follicle evolve separately. The evolution of what remains of the follicle results in the formation of the corpus luteum.

​​IV.Le corpus luteum.

The transformation of the follicle that start from the LH surge will rush after ovulation. Ovulatory discharge of LH an active plasmin. This plasmin that allows the acceleration mechanisms of disintegration of the ovary wall also allows the activation of collagenase. Activated collagenase acts on the granulosa and decouples gap junctions. The granulosa is vascularized and stop proliferating. Collagenase dissociated membrane Slavjanski and it becomes impervious to blood vessels and endocrine cells of the theca interna. The theca interna penetrate into the granulosa, the two cell types are mixed. All of these phenomena is that luteinization results in the formation of the corpus luteum. The corpus luteum is a temporary endocrine gland formed from lutein cells that provide a synthesis of female steroid hormones: estradiol and progesterone. If fertilization occurs the corpus luteum becomes the corpus luteum of pregnancy that persists for 3 months. Otherwise, the corpus luteum turns into a whitish substance, fibrous => the corpus albicans. V. The hormonal secretions At puberty, ovarian activity is cyclic of 28 days on average. The ovarian cycle is divided into two phases: pre-and post-ovulatory with a characteristic growth hormone that reflect different stages of folliculogenesis. In response to changes in ovarian hormones the uterus undergoes a series of changes that define the uterine cycle.

​​V.1) The ovarian cycle

The pre-ovulatory phase is characterized by a synthesis of estrogen in the ovaries two types of cells synthesize steroid hormones, are the cells of the theca interna that ensure the conversion of cholesterol into progesterone, granulosa celllues unable perform this conversion the import andogènes thèquaux to synthesize estrogen. The pre-ovulatory phase of the ovarian cycle is the follicular growth and increased production of estrogen and this under the stimulating effect of FSH. Estradiol is the estrogen most important by both its rate of production and its physiological role. The post-ovulatory phase corresponds to the appearance of progesterone, in fact the second part of the cycle is characterized by the appearance of the corpus luteum and progesterone synthesis in synergy with estrogens, lutein cells of corpora lutea to secrete both estrogen and progesterone.

​​V.2) The uterine cycle

The uterus has a thick muscular wall called the myometrium and mucosa that lines the light in the cervix called the endometrium. The endometrium is characterized by a connective tissue covered with epithelium. This epithelium consists of ciliated cells and goblet cells. It forms the gland that sink into the underlying connective tissue + / - deep depending on the phase of the cycle. The uterine cycle is a succession of three phases:

-1 Menstrual phase
-1 Proliferative phase (vascular + + +)
-1 Secretory phase

During the proliferative phase under the action of estrogen, the endometrium regenerates. Vascularization of the endometrium is + in + abundant. During the secretory phase, the blood supply becomes abundant in + + while the thickness of the endometrium is no longer increasing. It is the combined action of progesterone and estrogen, which prepares the endometrium for a possible pregnancy, stretch the arteries become sinuous spiral. In the absence of pregnancies arteries retract suddenly endometrial surface is suddenly deprived of its abundant blood supply and becomes necrotic. These phenomena characterize the menstrual phase.

VI.l changes in secretion of the lining of the cervix.

The cavity of the cervix secretes a thick mucus that can use the cervical mucus. The cervical mucus is the middle that allows the penetration of sperm into the uterus. The cervical mucus changes during the menstrual cycle, estrogen makes it + in + favor the penetration and survival of sperm during the first part of the cycle progressively as ovulation approaches. However progesterone makes it less favorable to sperm.

VII.l thermal cycle.

Body temperature measured in the morning upon waking changes during the cycle. It is less than 37 ° C during the first part of the cycle and then it goes to a temperature above 37 ° C at the time of ovulation. The temperature should remain set at above 37 ° C for at least 10 days. This rise of temperature is due to progesterone. She witnesses the presence of the corpus luteum and thus ovulation.