Phases of the menstrual cycle

The phases of the menstrual cycle are sequential hormonal and structural changes in the female body of a cyclic nature that ensure the realization of the reproductive function. The formation of the phase of the menstrual cycle is always dominated by the hormonal function of the ovaries, which affects not only the genital sphere, it modifies the work of the whole organism.

As in women the menstrual cycle has individual characteristics, the concept of its "norm" varies in a very wide range. To characterize the menstrual cycle, the following concepts are used:

- Duration. It is measured by the time interval between the onset of the next two menstruations, that is, the first day of the monthly period is the beginning of the next cycle and the end of the previous one. Most modern women celebrate the first day of each menstruation in the calendar, so it is very easy to calculate the duration of their menstrual cycle, counting the number of days between the marked dates. Menstrual calendar also always demonstrates any violations of the usual rhythm of menstruation. The normal duration of the menstrual cycle is considered, if it fits within 25-35 days, for the majority( 60%) it is equal to 28 days.

- The number of days of the cycle that occurs in menstrual bleeding. Menstruation is an integral part of any( and pathological too) menstrual cycle. Menstrual bleeding in 75% does not last longer than a week, but should not be too short( less than three days).

- Menstrual blood loss, its volume and duration. On average, it is 40 - 150 ml. The amount of a woman that is lost with every monthly blood is difficult to measure. Therefore, for the conventional "norm" is taken such an amount of menstrual blood, which does not require the use of more than four sanitary pads daily. It should be noted that this parameter is acceptable for situations when the change of gaskets corresponds to the established mode of their use.

There should not be a lot of clots or mucus in menstrual blood. In the normal course of menstrual blood loss decreases quantitatively from the first day to the last, and the number of "abundant" days, as a rule, does not exceed three.

It is also believed that menstrual blood loss should proceed painlessly, without disturbing the habitual life rhythm. Short-term weakly expressed pulling or aching sensations are allowed in the projection of the uterus in "abundant" days.

It should be noted that there is a small group of women( less than 30%) who have an individual "norm" of the menstrual cycle against the background of absolute gynecological health. As a rule, it is established from the first monthly and does not change until the end of menstrual function, that is, before menopause. If a woman's menstrual cycle differs from the conventional "norm", but is not accompanied by pathology and does not interfere with the realization of the reproductive function, it corresponds to the concept of an individual physiological "norm".

In addition to the conditional "norm", there are several strict parameters that any menstrual cycle should have, one of which is the presence of two phases.

1 phase of the menstrual cycle starts with the next menstrual bleeding and under the condition of the physiological cycle it is completed by a short period of ovulation. After ovulation, if there is no pregnancy, the second phase of the menstrual cycle starts, which ends with the beginning of the next menstruation. Two-phase cycles are not always accompanied by ovulation, but without the presence of both phases, ovulation is impossible. In terms of duration, both phases of the normal cycle are equivalent, but differ in hormonal and structural changes, which we will talk about a little later.

The phases of the menstrual cycle are formed with the obligatory participation of the complex biological processes of the entire female body, which are controlled by the central nervous system: the pituitary and the hypothalamus. Each of its phases is characterized by certain hormonal changes in the ovaries, which provoke a structural rearrangement of the endometrium.

The menstrual cycle is "looked after" by the hypothalamus. He in a cyclic rhythm secretes the biological active compounds( releasing hormones) that enter the pituitary gland. The pituitary gland is capable of producing hormones that affect the ovaries: follicle stimulating( FSH), luteinizing( LH) and prolactin. Each of them is secreted by the pituitary gland according to the phases of the cycle. Under the influence of pituitary hormones in the ovaries, certain changes occur that ensure the maturation of the egg. All events occurring during each menstrual cycle provide for the realization of the reproductive function.

Diagnosis of a two-phase menstrual cycle is very important for studying the causes of menstrual dysfunction and infertility. Laboratory methods for determining the level of the main hormones are used, their quantity and ratio are studied at different periods of the cycle. Ultrasound scanning allows you to visually assess the state of the endometrium and determine how structural changes in the mucous uterus correspond to the anticipated phase of the cycle. It also helps to study the structure of the follicular apparatus of the ovaries.

A woman can learn the nature of the menstrual cycle and herself, if she resorts to the basal temperature measurement technique, she is based on the ability of hormones of the second phase of the cycle( progesterone) to slightly increase the body temperature, which is measured rectally. If you measure this temperature daily and record the results in the graph, you can eventually see the characteristic graphic features of the two-phase ovulatory cycle. The measurements are carried out for several subsequent cycles. The method is recommended by specialists as one of the diagnostic procedures, but in the absence of menstrual dysfunction and / or infertility to measure basal temperature does not make sense.

Conditionally, both phases of the menstrual cycle are equal in duration, more often each lasts about 2 weeks. Since ovulation differentiates the menstrual cycle in two, it is conventionally assumed that the middle of the cycle belongs to it.

The first phase of the menstrual cycle

1 phase of the menstrual cycle implies the growth, maturation of the follicle and, accordingly, the ovum.

In the ovaries under the outer( white) shell there are many similar to thin-walled small vesicles of formations - follicles, and each of them serves as a receptacle for the ovum. The follicle, which has not reached maturity, is called primordial. Primordial follicles maturate symmetrically with the ovum, but within a period of one cycle, only one of them reaches its maximum maturity.

In the first, follicular phase of the cycle, the pituitary gland produces a follicle-stimulating hormone so that the follicle develops correctly. As the follicle ripens, its structure changes: it increases somewhat( up to 20 mm), is filled with a transparent follicular fluid, and the inside of the cavity is lined with a granular membrane. The primordial follicle that terminates the ripening stage is called a graaff bubble. The cells of the granulosa of the follicle secrete estrogens responsible for the proper development and growth of the oocyte.

In the first phase, the state of the endometrium also changes. Under the direct influence of estrogens( estradiol) in the endometrium, the process of increased proliferation( proliferation) of the outer( functional) mucous layer and the glandular structures located in it is triggered. The volume of the mucous uterus increases significantly, the structure of the mucosa becomes more loose, many new small blood vessels appear.

Certain structural changes are observed in the muscle layer( myometrium): its cells increase volume( hypertrophy).

The culmination of the first phase of the menstrual cycle is ovulation. When the egg reaches the maximum stage of development and no longer needs the nutrition and protection that the follicle provided to it, the wall of the graafovaya vesicle collapses and releases the egg. A viable egg remains for no longer than two days, and then, if fertilization does not happen, perishes.

Thus, the first phase of any menstrual cycle:

- coincides at the beginning with menstrual bleeding;

- occurs with the participation of follicle-stimulating hormone of the pituitary gland;

- characterized by maturation of the egg;

- is accompanied by the secretion of estrogens by the follicle;

- differs by processes of proliferation and vascularization of the functional layer of the endometrium;

- ends with the period of ovulation.

The extension of the first phase of the cycle indicates hormonal dysfunction. The long first phase of the menstrual cycle is more often associated with a violation of the processes of ovulation. Incomplete or completely absent ovulation provokes a hormonal failure: the ovaries do not stop secreting estrogens, and the uterus continues excessive, exceeding the norm, the proliferation of the endometrium. The result of such violations are often serious pathological changes, when the diagnosis of the causes of uterine dysfunctional bleeding and / or infertility reveals a long first phase of the menstrual cycle, as well as anovulation.

In order not to get confused in a variety of terms, patients need to remember that the first phase of the cycle can be called follicular( as characterized by the process of maturation of the follicle) or the proliferation phase( according to structural rearrangement in the endometrium).The second phase can also be characterized in different ways: it is called lutein or secretory.

The second phase of the menstrual cycle

The second, secretory, phase of the menstrual cycle starts right after the ovulation that has occurred. At the same time in the pituitary gland begins to develop another regulatory hormone - luteinizing( LH).When the egg leaves the ruptured follicle, it develops hemorrhage and thrombosis. The remaining cells of the granulosa shell begin to actively divide, germinate with small vessels( vascularization) and gradually transform into a new, temporarily existing hormonal structure called the "yellow body."It got its name because of the yellow substance produced by the cells of the granule shell of the destroyed graafovaya vesicle. After the beginning of the functioning of the yellow body, the maturation of new follicles stops and resumes only after the completion of the second phase.

The second, luteal phase of the menstrual cycle is closely related to the hormonal activity of the yellow body, which secrete the hormone progesterone. Immediately after ovulation, the increasing concentration of progesterone provokes further changes in the endometrium in the form of proliferation of the stroma and an increase in glandular structures. The glands of the mucosa begin to produce a secret secretively, their cavity expands, the cells of the stroma become voluminous. The secretory phase of the menstrual cycle, in fact, prepares the endometrium for the potential implantation of the fetal egg, that is - for the development of pregnancy. If fertilization occurs, the yellow body continues to function to retain the fetus in the uterus until the placenta is formed. Then, giving her the "relay", the yellow body is reduced.

If the egg does not fertilize, the yellow body, according to the law of feedback, begins to regress. The process of its reverse development is accompanied by a decrease in the concentration of progesterone. The yellow body dies shortly before the next menstruation, and in the endometrium processes of degeneration are triggered. The enlarged mucous layer is gradually torn away.

The luteal phase of the menstrual cycle always ends with bleeding. Menstruation is the result of complete rejection of the functional( superficial) epithelial layer of the uterine cavity, which is restored again after 5-6 days.

Thus, the 2nd phase of the menstrual cycle:

- occurs with the participation of the hormone progesterone, produced by the yellow body;

- is accompanied by processes of activation of glandular structures of the endometrium;

- differs mucosal degeneration against the background of death of the yellow body;

- ends with menstrual bleeding.