Uterine cycle. Endometrial thickness before menstruation: norm and deviations Fallopian tubes or oviducts

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Varieties

There are two types of desquamation:

physiological (occurs on the skin and some glandular organs);
pathological (occurs under the influence of inflammation on the mucous membranes or other processes).

Causes

Desquamation as a permanent phenomenon can be observed on the surface of the skin. During the process of skin desquamation, epidermal cells are removed. Physiological desquamation is also found during secretory processes that occur in some glandular organs. For example, the desquamation phase is observed in the mammary gland at the end of the lactation period.

As a pathological phenomenon, this process occurs during inflammation of the abdominal organs and mucous membranes. In this case, there is a violation of intercellular connections and detachment of the epithelium. As a rule, desquamated cells die, but sometimes they show viability and are capable of proliferative and phagocytic activity. An example is the vascular endothelium or alveolar pulmonary epithelium.

Due to disturbances in nervous trophism, the occurrence of exudative diathesis, the effects of helminthic infestations, and the appearance of diseases of the digestive system, desquamation of the tongue may occur.

Desquamation of the endometrium is observed when hormones act on the mucous membrane of the vagina and uterus. This process begins at the end of the menstrual cycle. During this period, the functional layer of the endometrium is rejected. The duration of this process usually does not exceed 5-6 days. The functional layer is areas of necrotic tissue, which is completely rejected during menstruation. At the beginning of the menstrual cycle, the desquamation phase of the endometrium ends.

Desquamation as a diagnostic method

Desquamation may be performed as a way to diagnose certain diseases. Thus, desquamation of the skin is often used to identify candidiasis, cancer and other disorders. A popular method for diagnosing benign and malignant neoplasms in the oral cavity is desquamation of the epithelium of the tongue. In this case, the smallest particles are scraped off for detailed examination. If the rules of this procedure are violated, desquamative glossitis develops.

Early stage of the proliferation phase. In this phase of the menstrual cycle, the mucous membrane can be traced in the form of a narrow echo-positive strip ("traces of the endometrium") of a homogeneous structure, 2-3 mm thick, located centrally.

Colpocytology. The cells are large, light-colored, with medium-sized nuclei. Moderate folding of cell edges. The number of eosinophilic and basophilic cells is approximately the same. Cells are placed in groups. There are few leukocytes.

Endometrial histology. The surface of the mucous membrane is covered with flattened columnar epithelium, which has a cubic shape. The endometrium is thin, there is no division of the functional layer into zones. The glands look like straight or somewhat winding tubes with a narrow lumen. In cross sections they have a round or oval shape. The epithelium of the glandular crypts is prismatic, the nuclei are oval, located at the base, and stain well. The cytoplasm is basophilic, homogeneous. The apical edge of the epithelial cells is smooth and clearly defined. On its surface, using electron microscopy, long microvilli are identified, which contribute to an increase in the surface of the cell. The stroma consists of spindle-shaped or stellate reticular cells with delicate processes. There is little cytoplasm. It is barely noticeable around the nuclei. In stromal cells, as in epithelial cells, single mitoses appear.

Hysteroscopy. In this phase of the menstrual cycle (up to the 7th day of the cycle), the endometrium is thin, smooth, pale pink in color, small hemorrhages are visible in some areas, and isolated areas of the endometrium are visible in a pale pink color that have not been rejected. The eyes of the fallopian tubes are clearly visible.

Middle proliferation phase. The middle stage of the proliferation phase lasts from 4-5 to 8-9 days after menstruation. The thickness of the endometrium continues to increase to 6-7 mm, its structure is homogeneous or with a zone of increased density in the center - the zone of contact of the functional layers of the upper and lower walls.

Colpocytology. A large number of eosinophilic cells (up to 60%). Cells are placed scatteredly. There are few leukocytes.

Endometrial histology. The endometrium is thin, there is no separation of the functional layer. The surface of the mucous membrane is covered with high prismatic epithelium. The glands are somewhat tortuous. The nuclei of epithelial cells are located in places at different levels, and numerous mitoses are observed in them. Compared to the early phase of proliferation, the nuclei are enlarged, less intensely colored, and some of them contain small nucleoli. From the 8th day of the menstrual cycle, a layer containing acidic mucoids forms on the apical surface of epithelial cells. Alkaline phosphatase activity increases. The stroma is swollen, loosened, and a narrow strip of cytoplasm is visible in the connective tissues. The number of mitoses increases. The stromal vessels are single, with thin walls.

Hysteroscopy. In the middle stage of the proliferation phase, the endometrium gradually thickens, becomes pale pink, and no vessels are visible.

Late stage of proliferation. In the late stage of the proliferation phase (lasts approximately 3 days), the thickness of the functional layer reaches 8-9 mm, the shape of the endometrium is usually teardrop-shaped, the central echo-positive line remains unchanged throughout the first phase of the menstrual cycle. Against a general echo-negative background, it is possible to distinguish short, very narrow echo-positive layers of low and medium density, which reflect the delicate fibrous structure of the endometrium.

Colpocytology. The smear contains predominantly eosinophilic superficial cells (70%), few basophilic ones. In the cytoplasm of eosinophilic cells there is granularity, the nuclei are small and pyknotic. There are few leukocytes. Characterized by a large amount of mucus.

Endometrial histology. There is some thickening of the functional layer, but there is no division into zones. The surface of the endometrium is covered with tall columnar epithelium. The glands are more tortuous, sometimes corkscrew-like. Their lumen is somewhat expanded, the epithelium of the glands is high, prismatic. The apical edges of the cells are smooth and distinct. As a result of intensive division and increase in the number of epithelial cells, the nuclei are at different levels. They are enlarged, still oval, and contain small nucleoli. Closer to the 14th day of the menstrual cycle, you can see a large number of cells containing glycogen. The activity of alkaline phosphatase in the epithelium of the glands reaches its highest level. The nuclei of connective tissue cells are larger, rounded, less intensely colored, and an even more noticeable halo of cytoplasm appears around them. The spiral arteries that grow from the basal layer at this time already reach the surface of the endometrium. They are still slightly tortuous. Under the microscope, only one or two peripheral vessels located nearby are identified.

Psteroscopy. In the late phase of proliferation, certain areas of the endometrium appear as thickened folds. It is important to note that if menstrual cycle proceeds normally, then in the proliferation phase the endometrium can have different thicknesses, depending on the location - thickened in the days and posterior wall of the uterus, thinner on the anterior wall and in the lower third part of the uterine body.

Early stage of the secretion phase. In this phase of the menstrual cycle (2-4 days after ovulation), the thickness of the endometrium reaches 10-13 mm. After ovulation, due to secretory changes (the result of the production of progesterone by the menstrual corpus luteum of the ovary), the structure of the endometrium becomes homogeneous again until the onset of menstruation. During this period, the thickness of the endometrium increases faster than in the first phase (by 3-5 mm).

Colpocytology. Characteristic deformed cells are wavy, with curved edges, as if folded in half; the cells are located in dense clusters, layers. The cell nuclei are small and pyknotic. The number of basophilic cells increases.

Histology of the endometrium. The thickness of the endometrium increases moderately compared to the proliferation phase. The glands become more tortuous, their lumen is expanded. The most characteristic sign of the secretion phase, in particular its early stage, is the appearance of subnuclear vacuoles in the epithelium of the glands. Glycogen granules become large, cell nuclei move from the basal to the central sections (indicating that ovulation has occurred). The nuclei, pushed aside by vacuoles into the central sections of the cell, are initially located at different levels, but on day 3 after ovulation (day 17 of the cycle), the nuclei that lie above large vacuoles are located at the same level. On the 18th day of the cycle, in some cells glycogen granules move to the apical sections of the cells, as if bypassing the nucleus. As a result of this, the nuclei again descend down to the base of the cell, and glycogen granules are located above them, which are located in the apical parts of the cells. The kernels are more rounded. There are no mitoses in them. The cytoplasm of the cells is basophilic. Acid mucoids continue to appear in their apical sections, while alkaline phosphatase activity decreases. The endometrial stroma is slightly swollen. Spiral arteries are tortuous.

Hysteroscopy. In this phase of the menstrual cycle, the endometrium is swollen, thickened, and forms folds, especially in the upper third of the uterine body. The color of the endometrium becomes yellowish.

Middle stage of secretion phase. The duration of the middle stage of the second phase is from 4 to 6-7 days, which corresponds to days 18-24 of the menstrual cycle. During this period, the greatest severity of secretory changes in the endometrium is observed. Echographically, this is manifested by a thickening of the endometrium by another 1-2 mm, the diameter of which reaches 12-15 mm, and its even greater density. At the border of the endometrium and myometrium, a rejection zone begins to form in the form of an echo-negative, clearly defined rim, the severity of which reaches its maximum before menstruation.

Colpocytology. Characteristic folding of cells, curved edges, accumulation of cells in groups, the number of cells with pyknotic nuclei decreases. The number of leukocytes increases moderately.

Endometrial histology. The functional layer becomes higher. It is clearly divided into deep and superficial parts. The deep layer is spongy. It contains highly developed glands and a small amount of stroma. The surface layer is compact, it contains less tortuous glands and many connective tissue cells. On the 19th day of the menstrual cycle, most of the nuclei are located in the basal part of the epithelial cells. All kernels are round and light. The apical section of the epithelial cells becomes dome-shaped, glycogen accumulates here and begins to be released into the lumen of the glands by apocrine secretion. The lumen of the glands expands, their walls gradually become more folded. The epithelium of the glands is single-row, with basally located nuclei. As a result of intense secretion, the cells become low, their apical edges are vaguely expressed, as if with teeth. Alkaline phosphatase completely disappears. In the lumen of the glands there is a secret that contains glycogen and acidic mucopolysaccharides. On day 23, the secretion of the glands ends. A perivascular decidual reaction of the endometrial stroma appears, then the decidual reaction becomes diffuse, especially in the superficial parts of the compact layer. The connective tissue cells of the compact layer around the vessels become large, round and polygonal in shape. Glycogen appears in their cytoplasm. Islands of predecidual cells are formed. A reliable indicator of the middle stage of the secretion phase, which indicates a high concentration of progesterone, are changes in the spiral arteries. Spiral arteries are sharply tortuous, form “skeins”, they can be found not only in the spongy, but also in the superficial parts of the compact layer. Until the 23rd day of the menstrual cycle, the tangles of the spiral arteries are most clearly expressed. Insufficient development of “coils” of spiral arteries in the endometrium of the secretory phase is characterized as a manifestation of weak function of the corpus luteum and insufficient preparation of the endometrium for implantation. The structure of the endometrium of the secretory phase, the middle stage (22-23 days of the cycle), can be observed with prolonged and increased hormonal function of the menstrual corpus luteum - persistence of the corpus luteum, and in the early stages of pregnancy - during the first days after implantation, with intrauterine pregnancy outside the implantation zone ; with progressive ectopic pregnancy evenly in all parts of the mucous membrane of the uterine body.

Hysteroscopy. In the middle phase of the secretion stage, the hysteroscopic picture of the endometrium does not differ significantly from that in the early phase of this stage. Often, endometrial folds take on a polyp-like shape. If the distal end of the hysteroscope is placed tightly to the endometrium, the glandular ducts can be seen.

Late stage of the secretion phase. Late stage of the second phase of the menstrual cycle (lasts 3-4 days). In the endometrium, pronounced trophic disorders occur due to a decrease in the concentration of progesterone. Sonographic changes in the endometrium associated with polymorphic vascular reactions in the form of hyperemia, spasms and thrombosis with the development of hemorrhages, necrosis and other dystrophic changes, slight heterogeneity (spotting) of the mucosa appears due to the appearance of small areas (dark “spots” - zones of vascular disorders), becomes clearly visible the rim of the rejection zone (2-4 mm), and the three-layer structure of the mucosa, characteristic of the proliferative phase, is transformed into a homogeneous tissue. There are cases when echo-negative zones of the endometrial thickness in the preovulatory period are mistakenly assessed by ultrasound as pathological changes.

Colpocytology. The cells are large, pale-colored, foamy, basophilic, without inclusions in the cytoplasm, the contours of the cells are indistinct and blurry.

Endometrial histology. The folding of the walls of the glands is enhanced, it has a dust-like shape on longitudinal sections, and a star-like shape on transverse sections. The nuclei of some epithelial cells of the glands are pyknotic. The stroma of the functional layer shrinks. Predecidual cells are close together and located around the spiral vessels diffusely throughout the compact layer. Among the predecidual cells there are small cells with dark nuclei - endometrial granular cells, which are transformed from connective tissue cells. On the 26-27th day of the menstrual cycle, in the superficial areas of the compact layer, lacunar expansion of capillaries into the stroma is observed. In the premenstrual period, spiralization becomes so pronounced that blood circulation slows down and stasis and thrombosis occur. A day before the onset of menstrual bleeding, a state of the endometrium occurs, which Schroeder called “anatomical menstruation.” At this time, you can find not only dilated and congested blood vessels, but also spasm and thrombosis, as well as small hemorrhages, edema, and leukocyte infiltration of the stroma.

Psteroscopy. In the late phase of the secretion stage, the endometrium acquires a reddish tint. Due to the pronounced thickening and folding of the mucosa, the eyes of the fallopian tubes cannot always be seen. Just before menstruation, the appearance of the endometrium can be mistakenly interpreted as endometrial pathology (polypoid hyperplasia). Therefore, the time of hysteroscopy must be recorded for the pathologist.

Bleeding phase (desquamation). During menstrual bleeding, due to a violation of the integrity of the endometrium due to its rejection, the presence of hemorrhages and blood clots in the uterine cavity, the echographic picture changes during the days of menstruation as parts of the endometrium with menstrual blood are discharged. At the beginning of menstruation, the rejection zone is still visible, although not completely. The structure of the endometrium is heterogeneous. Gradually, the distance between the walls of the uterus decreases and before the end of menstruation they “close” with each other.

Colpocytology. The smear contains foamy basophilic cells with large nuclei. A large number of erythrocytes, leukocytes, endometrial cells, and histocytes are also found.

Endometrial histology(28-29 days). Tissue necrosis and autolysis develop. This process begins from the superficial layers of the endometrium and is flammable in nature. As a result of vasodilation, which occurs after a prolonged spasm, a significant amount of blood enters the endometrial tissue. This leads to rupture of blood vessels and detachment of necrotic sections of the functional layer of the endometrium.

Morphological signs characteristic of the endometrium of the menstrual phase are: the presence of tissue permeated with hemorrhages, areas of necrosis, leukocyte infiltration, a partially preserved area of the endometrium, as well as tangles of spiral arteries.

Hysteroscopy. In the first 2-3 days of menstruation, the uterine cavity is filled with a large number of endometrial scraps from pale pink to dark purple, especially in the upper third. In the lower and middle third of the uterine cavity, the endometrium is thin, pale pink, with pinpoint hemorrhages and areas of old hemorrhages. If the menstrual cycle was full, then already before the second day of menstruation there is almost complete rejection of the uterine mucosa, only in certain areas of it small fragments of the mucous membrane are detected.

Regeneration(3-4 days of the cycle). After rejection of the necrotic functional layer, regeneration of the endometrium from the tissues of the basal layer is observed. Epithelization of the wound surface occurs due to the marginal glands of the basal layer, from which epithelial cells move in all directions onto the wound surface and close the defect. With normal menstrual bleeding under conditions of a normal two-phase cycle, the entire wound surface is epithelialized on the 4th day of the cycle.

Hysteroscopy. During the regeneration stage, against a pink background with areas of hyperemia of the mucosa, small hemorrhages are visible in some areas, and isolated areas of the endometrium of a pale pink color may be encountered. As the endometrium regenerates, areas of hyperemia disappear, changing color to pale pink. The angles of the uterus are clearly visible.

Article last updated 12/07/2019

A woman’s reproductive function is supported by a complex mechanism that ensures the relationship between processes in the reproductive organs and hormonal indicators. To prepare the reproductive organ for possible embryo implantation, the structure and thickness of the uterine tissue changes during each menstrual cycle. Most of the changes concern the intrauterine mucous layer - the endometrium, which undergoes modifications throughout the entire cycle.

It is important that the thickness of the endometrium before menstruation and immediately after its cessation is normal.

This makes it possible to ensure physiologically normal restoration (regeneration) of the functional sublayer of the uterus in subsequent menstrual cycles, and in case of successful conception, it allows the fertilized egg to settle inside the uterine cavity and create all the conditions for the full development of pregnancy.

Anatomically, the female uterus is represented by three main layers:
external – perimetry;
middle – myometrium;
internal – endometrium.

The endometrial uterine layer has a two-level structure and is represented by functional and basal epithelial sublayers. Purpose basal layer, located next to the myometrium - to create conditions for cellular growth of tissues of the functional sublayer, which is rejected during monthly bleeding if fertilization has not occurred.

The greatest changes throughout the menstrual cycle occur in functional layer, which contains many receptor cells that are highly sensitive to the produced hormones: estrogen and progesterone.

The endometrium, due to the presence of an extensive system of blood vessels in it, increases its volume under the influence of hormones. Gradually thickening deep into the uterus, it becomes loose, so that it is easier for the fertilized egg to gain a foothold in the tissues. If fertilization does not occur, the detachment of the endometrial layer is physiologically ensured, menstruation begins and the processes that ensure a new cycle are resumed.

Cycle phases

In a healthy woman, the inner lining of the uterus goes through 3 main phases. The thickness of the endometrium during these phases has its own standard indicators, which can be seen in the photo in the gynecological office.

By observing the process under ultrasound control and establishing that the thickness of the endometrial layer corresponds to the days of the cycle, one can form an opinion about the absence of hormonal disorders and the normal course of cyclic changes in the female body.

In the menstrual cycle there are:
proliferative phase;
secretory phase;
directly the bleeding phase, that is, the period of menstruation (desquamation).

During each phase, changes occur in the tissues of the ovaries and endometrium due to fluctuations in hormones. Because of this, the thickness of the endometrial layer varies by day of the cycle. Before the onset of menstruation, the thickening becomes maximum. Typically the entire cycle takes about 27-29 days. During this time, the mucous membrane is modified from minimal thickness to the state of an overgrown, loose structure that is rejected with menstruation.

Proliferation phase

It should begin immediately after the end of menstruation, approximately on the 5th day from the start of menstruation, and last from 12 to 14 days. During this phase, the endometrial layer grows from its minimum thickness of 2-3 millimeters, its preparation for the ovulatory process and possible fertilization begins.

The proliferation phase has 3 stages:

at the early stage (before the 7th day), the endometrial norm is from 4-5 mm to 7 mm in thickness, the density is reduced (hypoechoic), the layer is relatively uniform, looks pale pink and thin;
in the middle stage, the mucous membrane continues to thicken and grow, the endometrium 9 mm grows by the 9th day, by the 10th - up to 10 mm, acquires a rich pink tint;
the final stage (late proliferation) lasts from 10 to 14 days, the endometrial layer acquires a folded structure, characterized by thickening in areas of the fundus and posterior wall of the uterus, on average the endometrium is 13 mm.

For favorable fixation of the fertilized egg, the functional layer must be at least 11 mm-12 mm, this is the norm. Only with such a thickness of the endometrium will reliable implantation of the fertilized egg begin.

Secretion phase

When the secretion phase begins, which starts a couple of days after ovulation, the endometrial layer no longer grows at the same rate. On an ultrasound, you can see that significant changes in the structure have begun under the influence of progesterone, which is produced by the corpus luteum of the ovary.

This phase also consists of 3 stages:

At the early stage of secretion, the mucous membrane grows slowly, and restructuring begins in it. The thick endometrium swells even more and acquires a yellowish tint. On ultrasound, hyperechogenicity can be noted along the edges of the endometrium, which reaches 14-15 mm;
in the middle stage of secretion, which lasts from the 24th to the 29th day, the endometrium undergoes pronounced secretory transformations, becomes maximally dense and reaches a maximum thickness of 15-18 mm - this is the norm. The ultrasound picture reveals the appearance of a dividing line between the endometrium and myometrium, which represents a zone of exfoliation;
the late stage precedes the onset of menstruation. The corpus luteum involutions, the level of progesterone decreases, and the process of trophic changes in the overgrown layer begins. The endometrium has a thickness limit before menstruation - 1.8 cm. On ultrasound, you can see areas of dilated capillaries and the beginning of thrombotic processes, which subsequently lead to necrotic phenomena in the tissues, preparing them for rejection.

What is the maximum endometrial thickness considered normal? Doctors state that endometrium 12 mm, 14 mm, 16 mm, 17 mm are normal variants. But 19 mm is already considered to be exceeding the standard values.

Desquamation phase (immediately the period of menstruation)

During menstruation, the functional layer is destroyed and rejected, coming out in the form of menstrual bleeding. This phase lasts, on average, 4-6 days and is divided into 2 stages - rejection and recovery.

At the stage of rejection (days 1-2 of the cycle), the endometrial layer is normally 5-9 mm, it is hypoechogenic (decreased density), capillaries are deformed, burst, and menstruation begins.
At the regeneration stage, starting from the 3rd to the 5th day, the endometrium has a minimum thickness of 3 to 5 mm.

Delayed onset of menstruation

In the absence of pathological processes, the menstrual cycle is characterized by regularity and moderate blood loss. During puberty, there may be fluctuations in the length between periods. Sometimes it is impossible to accurately calculate when your next period will come.

In the absence of pregnancy, there may sometimes be a delay in the onset of menstruation due to hormonal imbalance. If there is an imbalance in the production of hormones, then the thickness of the uterine epithelium remains at the level of 12-14 mm with a delay. It does not decrease, there is no rejection, and there is no menstruation.

In some diseases of the uterus, there is a slowdown in the rejection of the functional layer, which affects the intensity and duration of menstruation. Excessive blood loss can occur after a spontaneous abortion, when the fertilized egg is incompletely separated and parts of it remain in the uterus.

Other factors that contribute to delays in the onset of menstruation include:

hormonal imbalance;
disruptions in the functioning of the endocrine system;
thyroid diseases;
excessive levels of physical activity, leading to a decrease in the production of sex hormones;

gynecological pathologies, for example, ovarian diseases;
a condition after an abortion, when, due to curettage, the endometrium recovers much more slowly than usual;
the use of oral hormonal contraceptives, the cancellation of which sometimes affects the regularity of the cycle for some time.

How long can the delay be? Doctors tend to consider a delay of menstruation within 7-10 days as the norm. If there is a delay of more than two weeks, you need to make sure that pregnancy has not occurred.

If a woman’s period does not come according to schedule, this is not a reason to panic. When there is irregularity in the monthly cycles, excessive scarcity, or, conversely, intense bleeding, the woman needs to consult a gynecologist. Proper treatment of pathologies will normalize the functioning of the reproductive organs and bring the size of the endometrium into line. Normal endometrial indicators throughout the entire cycle are evidence of women’s health and hormonal balance, which has a positive effect on the ability to conceive and bear a healthy child.

The total duration of the cycle is 28 days, but in some cases it can last up to 35 days. It depends on the individual characteristics of the female body.

The phases of the menstrual cycle are classified according to the nature of the cyclic changes occurring in the ovaries and endometrium (menstrual, proliferative and secretory). The follicular or menstrual stage begins on the first day of menstruation and is characterized by the production of gonadotropin-releasing hormone in the hypothalamus of the brain. GnRH, in turn, stimulates the secretion of follicle-stimulating hormone and luteinizing hormone.

The menstrual phase is accompanied by bloody discharge from the uterine cavity. If fertilization of the egg does not occur, the endometrial layer is rejected, this is accompanied by bleeding, which can last 3-7 days. Women are bothered by nagging, aching pain in the lower abdomen.

About 20 follicles begin to form in the ovaries, but usually only one (dominant) matures, reaching a size of 10–15 mm. The remaining cells undergo reverse development - artresia. The follicle continues to grow until LH surges. This ends the first phase of the menstrual cycle; its duration is 9–23 days.

Ovulatory phase

On the 7th day of the cycle, the dominant follicle is determined, which during the growth process reaches 15 mm and secretes estradiol.

The second phase of the menstrual cycle lasts 1–3 days and is accompanied by an increased release of luteinizing hormone. LH causes an increase in the level of prostaglandins and proteolytic enzymes, which promote perforation of the follicle capsule with the subsequent release of a mature egg. This process is called ovulation. A sharp increase in LH secretion can be observed from 16 to 48 hours, the release of the egg usually occurs after 24–36 hours.

Sometimes phase 2 of the menstrual cycle is accompanied by ovulatory syndrome. Rupture of the follicle and the leakage of a small amount of blood into the pelvic cavity is accompanied by pain in the lower abdomen on one side. Brown spotting may appear, and basal temperature rises. Such symptoms persist for up to 48 hours. Acute pain syndrome is observed in women suffering from chronic inflammatory diseases of the gynecological organs, and in the presence of adhesions.

The timing of ovulation is unstable; endocrine disorders, concomitant diseases, and psychoemotional disorders can affect it. Typically, follicle rupture occurs on days 6–16 of the menstrual cycle, which is 28 days. If the cycle lasts 35 days, then ovulation may occur on days 18–19.

The next phase of menstruation lasts from the moment of ovulation until the start of menstruation, lasting 14 days. After the release of the egg, the follicle begins to accumulate fat cells and luteal pigment, gradually turning into the corpus luteum. This temporary endocrine gland produces estradiol, androgens and progesterone.

Changes in hormonal balance affect the condition of the endometrium (inner layer of the uterus). The luteal phase is characterized by the proliferation of endometrial cells that secrete hormones. During this period, the uterus prepares for implantation of a fertilized egg.

If pregnancy occurs, the corpus luteum begins to intensively produce progesterone. This hormone:

promotes relaxation of the walls of the uterus;
prevents its contraction;
responsible for the secretion of breast milk.

The production of hormones by the corpus luteum continues until the placenta is formed.

If pregnancy does not occur, the temporary gland stops working and is destroyed, this leads to a decrease in the level of progesterone and estrogen. Necrotic destruction of cells occurs in the endometrial tissues, edematous processes are observed, and menstruation begins.

The suppression of FG and LH secretion stops, gonadotropins stimulate follicle maturation, and a new ovarian cycle begins.

Uterine cyclic processes

The duration of the uterine cycle corresponds to the duration of the ovarian cycle. Cyclic changes in the condition of the uterus are classified:

The menstrual period (desquamation) is accompanied by rejection of the endometrium and its release with blood from the opened vessels. The duration of this stage is 3–7 days. The period of desquamation coincides with the death of the corpus luteum.
The regeneration phase begins during the period of desquamation, approximately on the 5th–6th day. Restoration of the functional layer of the epithelium occurs due to the proliferation of gland remnants located in the basal layer.

The proliferative phase coincides with the follicular and ovulatory stages of the ovarian cycle. This stage begins with the growth of the follicle and its production of estrogens. Hormones promote epithelial renewal and proliferation of mucosal cells from the tissues of the uterine glands. The thickness of the epithelium increases 3–4 times, and the size of the tubular glands of the uterus also increases, but they do not secrete secretions.
The secretory stage is accompanied by the beginning of secretion production by the uterine glands. This period coincides with the development of the corpus luteum in the ovaries, and lasts from days 14 to 28 of the menstrual cycle. During the secretory phase, protrusions form in the walls of the uterus. A supply of microelements begins to be deposited in the mucous membrane, and enzyme activity increases. Thus, favorable conditions are created for the development of the embryo. If fertilization does not occur, the corpus luteum is destroyed, the functional layer of the endometrium is rejected and menstruation begins.

The vagina also undergoes cyclical changes. With the onset of the follicular phase, the epithelium of the mucous membranes begins to grow, and the secretion of mucin in the cervix increases. Cervical mucus thins and becomes similar to egg white, and the acidity level of the discharge changes. This is necessary for easier movement of sperm and increase their life expectancy. Epithelial cells in the vagina reach their maximum thickness with the onset of ovulation, the mucous membrane has a loose consistency. In the luteal phase, proliferation stops and desquamation occurs under the influence of progesterone.

In this phase cycle the mucous membrane of the uterus, especially its functional zone, is largely filled with blood. Due to the expansion of the capillaries, through which the material necessary for the formation of secretion is supplied along with the blood, stasis (stagnation) of blood gradually occurs in the vessels of the mucous membrane, with its subsequent transudation into the surrounding tissue of the lamina propria. As a result, the mucous membrane, saturated with blood transudate and mucous secretion of the glands, swells (acquires an edematous consistency) and softens, thereby creating favorable conditions for nidation of the embryo.

During phases of secretion in the ovary the corpus luteum functions, which towards the end of the phase begins to gradually degenerate and undergo reverse development. During this period, the egg cell, ejected from the Graafian follicle, moves along the oviduct; in the event of fertilization, it penetrates into the thus prepared uterine mucosa. The secretion phase, starting from the 14-15th day of the menstrual cycle, continues until the 28th day inclusive.

Desquamation phase(rejection - menstruum). In the event that fertilization and nidation of the egg cell to the mucous membrane of the uterus does not occur, the corpus luteum gradually dies, and the functional zone of the mucous membrane, oversaturated with blood in the secretion phase, becomes ischemic, with insufficient blood filling, due to vascular contraction and obstructed blood flow ; in connection with this, it becomes increasingly saturated with liquid and softens with simultaneous tissue degeneration.

Thus disintegrating, peeling and the degenerating tissue of the functional layer of the mucous membrane, impregnated with blood transudate and secretions, gradually in the form of pieces, together with the superficial epithelial layer, is torn away from the basal layer (decidua menstruationis). The rejected mucous membrane, together with the blood pouring out from the damaged vessels, mixes with the secretions of the uterine glands and is released from the uterus through the vagina.

This menstrual blood(menstruation) usually lasts four days, that is, starting from the first day of the menstrual cycle and ending with the fourth day inclusive.

In the ovary at this time, the reverse development of the corpus luteum continues, and a new follicle begins to mature, which represents the beginning of the re-restoration of the damaged mucous membrane.

Regeneration phase(postmenstrum). After desquamation, rejection of the functional layer of the uterine mucosa, the surface of its cavity is covered only by the exposed basal layer of the mucosa; at this time, the basal layer is very thin; the bases of the uterine glands are located in it. In the regeneration phase, due to the proliferation of epithelial cells of these remnants of the glands, the regeneration of the surface epithelium occurs, which then very quickly covers the wounded inner surface of the uterine cavity. This is immediately followed by a new proliferation phase of the next menstrual cycle.
The regeneration phase ends on the 5th day of the menstrual cycle.

Under regular The twenty-eight-day repetition of the uterine cycle and menstrual blood flow implies average periods within the framework of biological variations. The menstrual cycle may be subject to individual individual fluctuations; its deviations both in relation to the total duration of the entire cycle and in relation to the duration of its individual phases compared to the average period (from 24 to 32 days) do not mean anything abnormal or pathological, unless they are associated with other disorders or difficulties. Thus, if menstruation does not last for four days, then this is not proof of any disorder.
Three- or five-day menstrual bleeding is often observed.