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Menstrual Cycle

The menstrual cycle is the set of physiological phenomena of the woman's body prepares for possible fertilization and occurs most often on a regular basis.

The most visible manifestation of these changes is menstruation. The menstrual cycle begins at puberty and ends at menopause by depletion of ovarian follicles and increase in resistance of ovarian follicles to the action of gonadotropin.

This cycle is controlled by hormones. Its duration is usually from 28 days for women in Western countries , but is merely a convenient medium (28 days = 4 weeks) and represents neither the mean nor the mode of its distribution worldwide. In India, the average (standard deviation) was measured at 31.2 3.2 days in 1974 and 31.8 6.7 days in a 1992 study ^Subclass

In fact, the menstrual cycle described here comprises mainly the ovarian cycle, often called the menstrual cycle by abuse of language. The menstrual cycle in the strict sense is simply the period of blood loss: the corpus luteum turns into a white body and the ovarian cycle is the cycle of egg (oocyte II). This is the pattern of primary follicle to ovulation and corpus luteum remains to deliver progesterone.

Changes in body

Round hypothalamic

Neurons have a specific endocrine function since release a hormone called GnRH or GnRH (Gonadotropin Releasing Hormone), a pulsatile manner in the vascular system is hypothalamic-pituitary , unlike conventional neurons that release neurotransmitters at synapses; GnRH causes the pituitary (gland by cells of the adenohypophysis) of two gonadotropins or gonadotropins , FSH (follicle stimulating hormone) and LH (Luteinizing Hormone), changes in plasma levels of these hormones during the cycle define the pituitary hormone cycle.

Round pituitary

FSH, follicle-stimulating hormone is indispensable for follicle development and ensures the gametogenic maturation of a follicle cycle, the follicle de Graaf, and secondly it determines, with LH, the installation of endocrine function preantral follicle stage.
The plasma discharge of a high dose of FSH and LH above triggers the ovulation takes place 36 hours after the start of the ascent of the peak ovulation.
LH, luteinizing hormone , allows the formation of the corpus luteum during ^the 2nd phase of the cycle and is responsible for cell transformation of granulosa cells in large luteal cells (luteinization) source of progesterone.

Ovarian Cycle

The ovarian cycle involves the resumption of oogenesis (oocyte I to 2n chromosomes is blocked in prophase ^of 1st meiotic since fetal life), ovarian hormonal secretions necessary for the ovulation , uterine changes to the fertilization and the preparation of the endometrium to implantation.

The endocrine and exocrine function of the ovary as anatomical support the ovarian follicle, which also varies cyclically.

There are three cycles in the ovary:

follicular cycle
exocrine cycle corresponding to the resumption of oogenesis
endocrine cycle.

Cycles follicular

The follicles are contained in the cortical stroma. There are two types of follicles:

Evolutionary gametogenic follicles or with only one per cycle reaches maturity ( Graafian follicle ) which will lay an egg and two follicles which degenerate involutive.
There are different types of follicles corresponding to evolutionary stages of progressive maturation of the morphological structure, they are chronologically:
- the primordial follicle
- the primary follicle
- the secondary follicle
- tertiary follicles (preantral and cavitary)
- the follicle or mature Graafian follicle.

Each follicle contains an oocyte or egg first class I (2n chromosomes) blocked in prophase of ^the 1st meiosis (diplotene or diacynse).

primordial follicle

The primordial follicle is very small (40 to 50 microns) and is comprised of a thin shell containing the oocyte I; the oocyte nucleus has a large aspect dormant (the chromosomes are dispersed in a chromatin fine) and has 1 or 2 nucleoli; follicular shell is formed of a single layer of flattened epithelial cells, the follicle cells, surrounded by a thick basement membrane, the membrane Slavjanski.

Primary follicle

Differs from the primary follicle primordial follicle by the appearance of follicle cells that have become cubic.

Secondary follicle or pre-antral

The secondary follicle is characterized by the formation of a ² nd layer of cells, followed by a continuous increase in the number of cells forming the follicular granulosa ; parallel, the oocyte increases in volume I (40 microns in the primordial follicle, it passes gradually to a size of 60 microns) and is surrounded by a glycoprotein envelope, the zona pellucida.

Tertiary follicle or antral

The tertiary follicle is characterized by the appearance of the cavity or antrum in follicular granulosa. The granulosa cells surrounding the oocyte are the cumulus or germinal disc. The oocyte and its nucleus has grown to the size of a primary follicle. Connective tissue present around the follicle is differentiated into a well-vascularized theca interna with large lipid-rich cells that produce hormones and an external library containing large vessels.

De Graaf follicle

The follicle Graafian or preovulatory follicle or mature follicle reached its maximum volume (2 cm) and the oocyte I (120 microns), it protrudes from the surface of the ovary that distorts and attenuates at a small beach translucent stigma under the action of a plasma discharge of pituitary gonadotropins, FSH and LH.

The corpus luteum

Spawning takes place ovule 36 hours after the peak ovulation, the follicle de Graaf, emptied of its contents, sags and wrinkles and is the dehiscent follicle will become the corpus luteum.

The corpus luteum resulting from the transformation of follicle dehiscence Slavjanski membrane disappears, leaving penetrate the capillaries in the thecal granulosa, causing a transformation of follicle cells: they increase considerably in size, richer in fat, and secrete pigment slightly yellow, lutein , responsible for the pale yellow of the corpus luteum on the ovary fresh, is the phenomenon of luteinization

The lack of implementation will mean the corpus luteum end of life, and it will start a process of degeneration is going to do during the 14 days remaining (after ovulation). The 28th day, he will adopt a form of scarring (if there was no implantation) and take the name of corpus albicans = white body, which means the loss of endocrine function.

Ovary exocrine

This is the resumption of oogenesis under the action of estradiol.

Endocrine Ovary

The cells of the theca interna under the action of LH synthesize androgens ( steroids to 19 carbon atoms). These androgens are converted to estrogens (steroids to 18 carbon atoms) by the action of aromatase is synthesized by follicle cells under the effect of FSH.
Follicle cells also secrete a polypeptide hormone, the inhibin , which exerts a negative feedback on FSH secretion especially in the second half of the pre-ovulatory phase, which would be a cause of the involution of the follicles.
The dominant follicle , richer in the FSH receptor, thus sensitive to low plasma levels of this hormone is the only one to continue to mature and become the Graafian follicle
When estradiol is maintained at a certain rate for 48 hours, there is a positive feedback on LH secretion triggers the LH surge.
This peak of LH discharge or ovum, is directly responsible for ovulation.

Round tubal

The fallopian tube has a quadruple role in reproduction:

The flag ensures uptake of the egg and it surrounds the ovary of the many fringe mobile, encloses more or less at the time of ovulation and the egg gets laid; uptake of the egg from the fallopian tube is facilitated by the existence of a common origin of serous peritoneal guide the egg to the opening of the pavilion (ostium abdominal), then returns the serum into the peritoneal cavity through the slots of the nodes tubal mucosa
The egg reaches the bulb in a few hours it is his level that achieves fertilization , the fertilized egg is then called egg or zygote.

Round uterine

Myometrium

There are variations of uterine tone.

Endometrium

By convention, the first day of the cycle described below is the first day of menstruation. The growth of the endometrium functional again on 5 ^th day and continues throughout the life cycle: from 0.5 mm at the end of the menstrutation, it changes to 3 mm at the time of ovulation, reaching 5 to 28 mm ^th day of the cycle.

Phase scaling (J1-J4)

Fall in plasma estrogen and progesterone due to degeneration of the corpus luteum causes a collapse of the functional area of the endometrium with ischemia (due to rhythmic contractions of the arterioles) resulting in necrosis of the glands, and vessels of the chorion responsible for menstruation.
There remains only the residual area, 0.5 mm thick, persists with few dead ends gland open into the uterine cavity and small vessels

Regeneration (J5-J8)

The secretion of 17-beta-estradiol stimulates the growth of the endometrium from the cul-de-sacs glandular epithelium surface is reformed, the glands lengthen a little, and arterioles; mitoses are numerous in the surface epithelium, glands and the chorion.

Proliferation phase (J9-J14)

Mucosa continues to grow; glands and arteries lengthen faster than the chorion, resulting in a slight sinuosity of the glands and a spiraling of arteries early in depth, epithelial cells increase in height and have a clear apical.

Glandular phase of processing (J15-J21)

Secretory phase begins under the combined action of estrogen and progesterone, the glands become longer and more sinuous, spiraling the arterioles increasing, progesterone induces the secretion of glycogen in the basal pole of cells, nuclei are center position, or apical.

Phase of glandular secretion (J22-J28)

The glands become very twisted, it is called glands sawtooth or branched glands, glandular light being distorted by spikes or thorns conjunctival chorion; glycogen won the apical pole and is excreted from the cell c ' is the phase of secretion and excretion; arterioles reach their maximum spiraling; the appearance of glands and arteries is that they grow much faster than the chorion, arterioles have a length 10 times the thickness chorion.

In terms of cervical

Two changes are under the control of ovarian hormones:

Muscle tone varies according to the cycle
The composition of the mucus secreted by the glandular cells of the cervix.

Pre ovulatory

Unimportant at the beginning of the cycle, it becomes increasingly abundant and "shooting" under the effect of estrogen until the ovulatory phase.

Ovulatory phase

At the time of ovulation , it is particularly clear because rich in water, its spinnbarkeit is maximum, its pH alkaline and the network mesh glycoproteins is very wide and stretched longitudinally all these conditions favor the survival of spermatozoa and their crossing col.

Post ovulatory phase

Under the effect of progesterone on cervical mucus coagulates and forms, against microbial agents, a physical barrier (meshed network and cross-glycoprotein) and biochemical, including its alkaline pH and by lysozyme , an enzyme bacteriolytic.

Vagina

The content is composed of the vaginal mucus, exudation of watery, vaginal exfoliated cells and inflammatory cells more or less numerous (neutrophils and histiocytes) and is normally rich in glycogen from the secretory cells of the genital tract and cells intermediate scaly; flora is the most common saprophytic flora consisting of lactic lactobacilli, bacilli Dderlein, which have the ability to convert glycogen to lactic acid responsible for the acidity of vaginal environment.

Hormonal Regulations

During the second half of the previous cycle, the high rate of estradiol and progesterone acting via the hypothalamic-pituitary suppresses the production of FSH and LH by the pituitary gland. Declining production of estradiol and progesterone by the corpus luteum at the end of the cycle removes this suppression and the FSH levels rise.

The follicles in the ovaries of FSH require a threshold below which no stimulation occurs. Initially the values of FSH are below this threshold, but they increase slowly until the threshold is crossed and when a group of follicles is stimulated into active growth. Several days of growth are needed before the follicles begin to produce estradiol which is secreted into the bloodstream and reach the hypothalamus to provide a signal that the threshold has been reached. There is also an intermediate rate of FSH production which must be exceeded before a follicle is brought to its full ovulatory response, and a maximum rate that should not be exceeded if too many follicles are stimulated and ovulations occur. The maximum rate is only 20% above the threshold and therefore precise feedback control of FSH production by the estrogen produced by the follicles is essential.

Near ovulation, the follicle produces rapidly increasing levels of estradiol. This hormone stimulates the production of cervical mucus and also suppresses the production of FSH, which passes under the threshold value, thus removing the necessary input to other follicles that are in competition for the race to ovulation.

The fall of FSH also induces a mechanism of maturation within the follicle which makes it responsive to the second pituitary gonadotropin, LH.

The high levels of estradiol also activates a positive feedback mechanism in the hypothalamus which causes massive discharge of LH by the pituitary gland. This LH surge is the trigger that initiates the rupture of the follicle (ovulation) usually 24 to 36 hours after its commencement. Ovarian production of estradiol drops sharply between the interval between the LH surge and ovulation.

After ovulation, the follicle that ruptured is transformed into a corpus luteum and the production of the second ovarian hormone, progesterone, increases rapidly at the same time as estradiol. This progesterone causes the abrupt change in the characteristics of cervical mucus. The disappearance of the corpus luteum (around the ^26th day) of the ovarian cycle (when not fertilization) stops the synthesis of progesterone and induced shedding of part of the endometrium, which covers an period of 3 to 5 days and is characterized by bleeding. The first day of bleeding is also the first day of the new cycle.

Exploration of the menstrual cycle

Clinical

Observation of cervical mucus

The physical properties of cervical mucus varies during the menstrual cycle under hormonal influence.

Incipient follicular phase (before ovulation), the cervical mucus has a narrow mesh. In addition, the external opening of the cervix is closed.
In pre-ovulatory phase, under the influence of estrogen, cervical mucus is loose, it is transparent, its abundance and increase spinnbarkeit; allowing the ascent of sperm. At this time cycle, the external opening of the cervix is open.
Luteal phase, under the influence of progesterone (secreted by the corpus luteum), cervical mucus becomes less abundant and its viscosity increases.

Taking the temperature

There are temperature variations during the menstrual cycle. When ovulation was increased body temperature of about 0.5 C, and thus that time, the woman knows she is in ovulatory phase.