Female reproductive cycle. Age-related changes in the organs of the female reproductive system

In women with the onset of puberty, ovulation periodically repeats. The sexual cycle lasts 27-28 days. It is divided into four periods: 1) pre-ovulation, 2) ovulation, 3) post-ovulation (metaoestrus), 4) rest period. Each of these periods is characterized by certain changes in the body (Fig. 110).

Pre-ovulation period. During this period, preparation for pregnancy occurs. In many species of animals with seasonal mating, the preovulation period is at the same time a period of preparation of the female reproductive apparatus for sexual intercourse. During this period, they are in heat and the female allows the male to have sexual intercourse.

In the preovulation period in women, the uterus increases in size and becomes full of blood; the mucous membrane of the uterus and its glands grow; peristaltic contractions of the uterine (fallopian) tubes and the muscular layer of the uterus intensify and become more frequent; the vaginal mucosa grows, and the number of deflated epithelial cells in the vaginal mucus increases. The cause of all these changes is the increased secretion of follicle-stimulating hormone from the pituitary gland.

Follicle-stimulating hormone also affects immature female animals. If such females are given this hormone daily, they will experience changes in the uterus and vagina characteristic of the preovulation period and ovulation may occur. If the pituitary gland is surgically removed in sexually mature female animals at the beginning of the preovulation period, then the development of preovulatory changes in the uterus and vagina stops and ovulation does not occur.

All preovulatory changes are caused by gonadotropic hormones of the pituitary gland due to their effect on the intrasecretory function of the ovaries. At this time, increased production of estrogens occurs in the ovaries, which stimulate the growth of the uterus and its mucous membrane, proliferation of the vaginal mucous epithelium and increase contractions of the uterus and fallopian tubes. If women who have had their ovaries removed for medical reasons and, as a result, have no sexual cycle, are administered estrogens in increasing quantities for several days, then they experience typical preovulatory changes in the uterus and vagina.

Rice. 110. Changes in the ovary and uterine lining during a normal menstrual cycle

(a-b) and during the menstrual cycle ending in pregnancy (b-d) (diagram).

1 - level of estrogen in the blood; 2 - progesterone level in the blood; 3 - follicle and corpus luteum of cycle a - b;

4 - follicle and corpus luteum of the b-g cycle; 5-changes in the uterine mucosa. The numbers below are

days of the cycle.

In a normal body, a gradually increasing amount of follicle-stimulating hormone accelerates the final maturation of the most mature of the vesicular ovarian follicles (Graafian vesicles). The surface of this vesicle ruptures and an egg is released from it - in other words, ovulation occurs.

Ovulation period. This period begins from the moment the vesicular ovarian follicle ruptures, the egg leaves it and moves through the fallopian tube into the uterus. During the period of passage through the fallopian tube, fertilization of the egg can occur. A fertilized egg, entering the uterus, attaches to its mucous membrane. The sexual cycle is interrupted at this point and pregnancy occurs. After the release of the egg, in place of the bursting vesicular ovarian follicle, the corpus luteum begins to develop, the cells of which produce the hormone progesterone. At the same time, estrogen production in the ovaries continues: it is secreted by numerous maturing follicles.

The egg released from the bursting vesicular ovarian follicle is directed into the fallopian tube by the movements of the ciliated epithelium. The contraction of the smooth muscles of the tubes at this time is enhanced under the influence of the increased amount of estrogen in the blood. Thanks to this, the egg is initially pushed through the tube quite quickly. As the developing ovarian corpus luteum secretes more and more progesterone, peristaltic contractions of the tubes become less frequent and weaker, as progesterone counteracts the stimulating effect of estrogen on the contractions of the muscles of the tubes and uterus. In general, it takes about 3 days for an egg to travel through the tube to the uterus. If fertilization of the egg does not occur, then the post-ovulation period begins.

Post-ovulation period. Women begin menstruation during this period. Animals (with the exception of monkeys) do not menstruate. An unfertilized egg, having entered the uterus, remains alive for several days and then dies. Meanwhile, under the influence of progesterone, the secretion of gonadotropic hormones by the anterior pituitary gland decreases. The decrease in follicle-stimulating hormone of the pituitary gland leads to a decrease in the formation of estrogen in the ovaries, therefore, the factor that caused and maintained preovulatory changes in the tubes, uterus and vagina is eliminated. The loss of the luteinizing hormone of the pituitary gland causes atrophy of the corpus luteum with its replacement by a connective tissue scar, as a result of which the ovarian production of progesterone ceases. Preovulatory changes in the uterus, tubes and vagina begin to decrease.

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Female reproductive system:
Ovarian-menstrual cycle; age-related changes; hormonal regulation

Sexual cycle

The ovarian-menstrual cycle is sequential changes in the function and structure of the organs of the female reproductive system, regularly repeating in the same order. In women and female great apes, sexual cycles are characterized by regular uterine bleeding (menstruation).

Most women who reach puberty have menstrual periods regularly. 28 days. In the ovarian-menstrual cycle, three periods or phases are distinguished: menstrual (endometrial desquamation phase), which ends the previous menstrual cycle, postmenstrual period (endometrial proliferation phase) and, finally, premenstrual period (functional phase, or secretion phase), during which preparing the endometrium for possible implantation of the embryo if fertilization occurs.

Menstrual period. It consists of desquamation, or rejection, of the functional layer. In the absence of fertilization, the intensity of secretion of progesterone by the corpus luteum sharply decreases. As a result, the spiral arteries supplying the functional layer of the endometrium become spasmed. Subsequently, non-rotic changes and rejection of the functional layer of the endometrium occur.

The basal layer of the endometrium, fed by the straight arteries, continues to be supplied with blood and is a source for the regeneration of the functional layer in the subsequent phase of the cycle.

On the day of menstruation, there are practically no ovarian hormones in a woman’s body, since the secretion of progesterone stops, and the secretion of estrogen (which was prevented by the corpus luteum while it was in its prime) has not yet resumed.

Regression of the corpus luteum disinhibits the growth of the next follicle, and estrogen production is restored. Under their influence, endometrial regeneration is activated in the uterus - epithelial proliferation increases due to the bottoms of the uterine glands, which are preserved in the basal layer after desquamation of the functional layer. After 2-3 days of proliferation, menstrual bleeding stops and the next postmenstrual period begins. Thus, the postmenstrual phase is determined by the influence of estrogens, and the premenstrual phase by the influence of progesterone.

Postmenstrual period. This period begins after the end of menstruation. At this moment, the endometrium is represented only by the basal layer, in which the distal parts of the uterine glands remain. The regeneration of the functional layer that has already begun allows us to call this period the proliferation phase. It lasts from the 5th to the 14th...15th day of the cycle. Proliferation of the regenerating endometrium is most intense at the beginning of this phase (5…11th day of the cycle), then the rate of regeneration slows down and a period of relative rest begins (11…14th day). The uterine glands grow quickly in the postmenstrual period, but remain narrow, straight and do not secrete.

As already mentioned, endometrial growth is stimulated by estrogens, which are produced by growing follicles. Consequently, during the postmenstrual period, another follicle grows in the ovary, which reaches the mature (tertiary, or vesicular) stage by the 14th day of the cycle.

Ovulation occurs in the ovary on the 12th...17th day of the menstrual cycle, i.e. approximately halfway between two regular menstruation periods. Due to the participation of ovarian hormones in the regulation of uterine restructuring, the described process is usually called not the menstrual, but the ovarian-menstrual cycle.

Premenstrual period. At the end of the postmenstrual period, ovulation occurs in the ovary, and in place of the burst vesicular follicle, a corpus luteum is formed, producing progesterone, which activates the uterine glands, which begin to secrete. They increase in size, become convoluted and often branch out. Their cells swell, and the lumens of the glands are filled with secreted secretions. Vacuoles containing glycogen and glycoproteins appear in the cytoplasm, first in the basal part, and then shifting to the apical edge. The mucus secreted abundantly by the glands becomes thick. In areas of the epithelium lining the uterine cavity between the mouths of the uterine glands, the cells acquire a prismatic shape, and cilia develop at the tops of many of them. The thickness of the endometrium increases compared to the previous postmenstrual period, which is caused by hyperemia and accumulation of edematous fluid in the lamina propria. Lumps of glycogen and droplets of lipids are also deposited in the cells of the connective tissue stroma. Some of these cells differentiate into decidual cells.

If fertilization has occurred, the endometrium participates in the formation of the placenta. If fertilization does not take place, then the functional layer of the endometrium is destroyed and rejected during the next menstruation.

Cyclic changes in the vagina. With the beginning of endometrial proliferation (on the 4-5th day after the end of menstruation), i.e. in the postmenstrual period, epithelial cells in the vagina noticeably swell. On the 7-8th day, the intermediate layer of compacted cells differentiates in this epithelium, and by the 12-14th day of the cycle (by the end of the postmenstrual period), the cells in the basal layer of the epithelium swell greatly and increase in volume. In the upper (functional) layer of the vaginal epithelium, the cells loosen and lumps of keratohyalin accumulate in them. However, the keratinization process does not reach complete keratinization.

In the premenstrual period, deformed, compacted cells of the functional layer of the vaginal epithelium continue to be rejected, and the cells of the basal layer become denser.

The condition of the vaginal epithelium depends on the level of ovarian hormones in the blood, therefore, based on the picture of the vaginal smear, one can judge the phase of the menstrual cycle and its disorders.

Vaginal smears contain desquamated epithelial cells and may contain blood cells - leukocytes and erythrocytes. Among epithelial cells, there are cells at different stages of differentiation - basophilic, acidophilic and intermediate. The ratio of the number of the above cells varies depending on the phase of the ovarian-menstrual cycle. In the early, proliferative phase (7th day of the cycle), surface basophilic epithelial cells predominate; in the ovulatory phase (11-14th day of the cycle), superficial acidophilic epithelial cells predominate; in the luteal phase (21st day of the cycle), the content of intermediate epithelial cells increases with large nuclei and leukocytes; in the menstrual phase, the number of blood cells - leukocytes and erythrocytes - increases significantly.

During menstruation, erythrocytes and neutrophils predominate in the smear; epithelial cells are found in small numbers. At the beginning of the postmenstrual period (in the proliferative phase of the cycle), the vaginal epithelium is relatively thin, and in the smear the content of leukocytes quickly decreases and epithelial cells with pyknotic nuclei appear. By the time of ovulation (in the middle of the ovarian-menstrual cycle), such cells in the smear become predominant, and the thickness of the vaginal epithelium increases. Finally, in the premenstrual phase of the cycle, the number of cells with a pyknotic nucleus decreases, but desquamation of the underlying layers, the cells of which are detected in the smear, increases. Before the onset of menstruation, the content of red blood cells in the smear begins to increase.

Age-related changes in the organs of the female reproductive system

The morphofunctional state of the organs of the female reproductive system depends on age and activity of the neuroendocrine system.

Uterus. In a newborn girl, the length of the uterus does not exceed 3 cm and, gradually increasing during the prepubertal period, reaches its final size upon reaching puberty.

Towards the end of the childbearing period and in connection with the approach of menopause, when the hormone-forming activity of the ovaries weakens, involutive changes begin in the uterus, primarily in the endometrium. Luteinizing hormone deficiency in the transitional (premenopausal) period is manifested by the fact that the uterine glands, while still retaining the ability to grow, no longer function. After menopause is established, endometrial atrophy progresses rapidly, especially in the functional layer. In parallel, muscle cell atrophy develops in the myometrium, accompanied by connective tissue hyperplasia. In this regard, the size and weight of the uterus undergoing age-related involution are significantly reduced. The onset of menopause is characterized by a decrease in the size of the organ and the number of myocytes in it, and sclerotic changes occur in the blood vessels. This is a consequence of decreased hormone production in the ovaries.

Ovaries. In the first years of life, the size of a girl’s ovaries increases mainly due to the growth of the brain. Follicular atresia, which progresses in childhood, is accompanied by the proliferation of connective tissue, and after 30 years, the proliferation of connective tissue also affects the ovarian cortex.

The attenuation of the menstrual cycle during menopause is characterized by a decrease in the size of the ovaries and the disappearance of follicles in them, and sclerotic changes in their blood vessels. Due to insufficient production of lutropin, ovulation and the formation of corpus luteum do not occur and therefore the ovarian-menstrual cycles first become anovulatory, and then stop and menopause.

Vagina. Morphogenetic and histogenetic processes leading to the formation of the main structural elements of the organ are completed by the period of puberty.

After the onset of menopause, the vagina undergoes atrophic changes, its lumen narrows, the folds of the mucous membrane are smoothed out, and the amount of vaginal mucus decreases. The mucous membrane is reduced to 4...5 layers of cells that do not contain glycogen. These changes create conditions for the development of infection (senile vaginitis).

Hormonal regulation of the female reproductive system

Clitoris in embryonic development and structure it corresponds to the dorsal part of the male penis. It consists of two erectile cavernous bodies ending in a head, which is covered with stratified squamous epithelium, slightly keratinized.

Innervation. The external genitalia, especially the clitoris, are abundantly supplied with various. Free nerve endings branch in the epithelium of these organs. In the connective tissue papillae of the lamina propria of their mucous membrane there are tactile nerve corpuscles, and in the dermis there are encapsulated genital corpuscles. Lamellar bodies are also found in the labia majora and clitoris.

Mammary gland

The histofunctional characteristics of the mammary glands were given earlier in the topic.

Some terms from practical medicine:

• menopause, menopause, menopause ( climax; Greek klimax ladder; climacterium; Greek klimakter step (ladders), turning point) - a period of life (both men and women) during which the cessation of generative function occurs;
• menopause (menopause; meno-Greek men month + Greek pausis cessation, break) - the second phase of the menopausal period, occurring after the last menstrual-like bleeding and characterized by the cessation of cyclic changes in the endometrium and reproductive function, progressive involution of the genital organs and a decrease in the secretion of sex hormones;
• menophobia (menophobia; meno- + phobia) - obsessive fear - fear of menstruation and (or) associated unpleasant sensations;
• vaginismus (vaginismus; lat. vagina vagina; synonym: vulvism, colpospasm) - reflex spastic contraction of the muscles of the vestibule of the vagina and pelvic floor, complicating sexual intercourse or gynecological examination;
• vulvovaginitis (vulvovaginitis; vulva - female external genitalia + lat. vagina vagina + -itis) - inflammation of the female external genitalia and vagina;
• colpitis -- (colpitis; kolp - Greek kolpos depression, sinus, vagina + -itis, synonym: vaginitis, endocolpitis) - inflammation of the vaginal mucosa;

The reproductive function of women is carried out primarily due to the activity of the ovaries and the uterus, since the egg matures in the ovaries, and in the uterus, under the influence of hormones secreted by the ovaries, changes occur in preparation for the reception of a fertilized egg. The reproductive period is characterized by the ability of a woman’s body to reproduce offspring; The duration of this period is from 17-18 to 45-50 years. The reproductive, or childbearing, period is preceded by the following stages of a woman’s life: intrauterine; newborns (up to 1 year); childhood (up to 8-10 years); prepubertal and pubertal age (up to 17-18 years). The reproductive period transitions into menopause, in which premenopause, menopause and postmenopause are distinguished.

The menstrual cycle is one of the manifestations of complex biological processes in a woman’s body. The menstrual cycle is characterized by cyclic changes in all parts of the reproductive system, the external manifestation of which is menstruation.

Menstruation is bloody discharge from a woman’s genital tract that periodically occurs as a result of the rejection of the functional layer of the endometrium at the end of a two-phase menstrual cycle. The first menstruation (menarhe) is observed at the age of 10-12 years, but for 1 - 1.5 years after this, menstruation may be irregular, and then a regular menstrual cycle is established.

The first day of menstruation is conventionally taken as the first day of the menstrual cycle. Therefore, the length of the cycle is the time between the first days of the next two menstruation periods. For 60% of women, the average length of the menstrual cycle is 28 days, ranging from 21 to 35 days. The amount of blood loss on menstrual days is 40-60 ml, on average 50 ml. The duration of normal menstruation is from 2 to 7 days.

Ovaries. During the menstrual cycle, follicles grow in the ovaries and the egg matures, which eventually becomes ready for fertilization. At the same time, sex hormones are produced in the ovaries, which ensure changes in the mucous membrane of the uterus, capable of receiving a fertilized egg.

Sex hormones (estrogens, progesterone, androgens) are steroids; granulosa cells of the follicle, cells of the inner and outer layers, take part in their formation. Sex hormones synthesized by the ovaries affect target tissues and organs. These include the genital organs, primarily the uterus, mammary glands, spongy bones, brain, endothelium and vascular smooth muscle cells, myocardium, skin and its appendages (hair follicles and sebaceous glands), etc. Direct contact and specific binding of hormones to target cell is the result of its interaction with the corresponding receptors.

The biological effect is provided by free (unbound) fractions of estradiol and testosterone (1%). The bulk of ovarian hormones (99%) are in a bound state. Transport is carried out by special proteins - steroid-binding globulins and nonspecific transport systems - albumin and erythrocytes.

A - primordial follicle; b - preantral follicle; c - antral follicle; d - preovulatory follicle: 1 - oocyte, 2 - granulosa cells (granular zone), 3 - theca cells, 4 - basement membrane.

Estrogenic hormones contribute to the formation of genital organs and the development of secondary sexual characteristics during puberty. Androgens influence the appearance of hair on the pubis and armpits. Progesterone controls the secretory phase of the menstrual cycle and prepares the endometrium for implantation. Sex hormones play an important role in the development of pregnancy and childbirth.

Cyclic changes in the ovaries include three main processes:

1. Growth of follicles and formation of a dominant follicle.

2. Ovulation.

3. Education, development and regression of the corpus luteum.

At the birth of a girl, there are 2 million follicles in the ovary, 99% of which undergo atresia throughout life. The process of atresia refers to the reverse development of follicles at one of the stages of its development. By the time of menarche, the ovary contains about 200-400 thousand follicles, of which 300-400 mature to the ovulation stage.

It is customary to distinguish the following main stages of follicle development (Fig. 2.12): primordial follicle, preantral follicle, antral follicle, preovulatory follicle.

The primordial follicle consists of an immature egg, which is located in the follicular and granulosa (granular) epithelium. The outside of the follicle is surrounded by a connective membrane (theca cells). During each menstrual cycle, 3 to 30 primordial follicles begin to grow and form preantral, or primary, follicles.

Preantral follicle. As growth begins, the primordial follicle progresses to the preantral stage, and the oocyte enlarges and is surrounded by a membrane called the zona pellucida. Granulosa epithelial cells undergo proliferation, and the theca layer is formed from the surrounding stroma. This growth is characterized by an increase in estrogen production. Cells of the granulosa layer of the preantral follicle are capable of synthesizing three classes of steroids, while much more estrogens are synthesized than androgens and progesterone.

Antral, or secondary, f o l l i k u l. It is characterized by further growth: the number of cells of the granulosa layer producing follicular fluid increases. Follicular fluid accumulates in the intercellular space of the granulosa layer and forms cavities. During this period of folliculogenesis (8-9 days of the menstrual cycle), the synthesis of sex steroid hormones, estrogens and androgens is noted.

According to the modern theory of sex hormone synthesis, androgens - androstenedione and testosterone - are synthesized in theca cells. Androgens then enter the granulosa layer cells and are aromatized into estrogens.

Dominant follicle. As a rule, one such follicle is formed from many antral follicles (by the 8th day of the cycle). It is the largest and contains the largest number of granulosa layer cells and receptors for FSH and LH. The dominant follicle has a richly vascularized theca layer. Along with the growth and development of the dominant preovulatory follicle in the ovaries, the process of atresia of the remaining (90%) growing follicles occurs in parallel.

The dominant follicle in the first days of the menstrual cycle has a diameter of 2 mm, which within 14 days at the time of ovulation increases to an average of 21 mm. During this time, there is a 100-fold increase in the volume of follicular fluid. The content of estradiol and FSH sharply increases in it, and growth factors are also determined.

Ovulation is the rupture of the preovular dominant (tertiary) follicle and the release of the egg. By the time of ovulation, the process of meiosis occurs in the oocyte. Ovulation is accompanied by bleeding from the destroyed capillaries surrounding the theca cells. It is believed that ovulation occurs 24-36 hours after the formation of the preovulatory estradiol peak. Thinning and rupture of the wall of the preovulatory follicle occurs under the influence of the enzyme collagenase. Prostaglandins F2a and E2 contained in follicular fluid also play a certain role; proteolytic enzymes produced in granulosa cells; oxytocin and relaxin.

After the release of the egg, the resulting capillaries quickly grow into the cavity of the follicle. Granulosa cells undergo luteinization: the volume of their cytoplasm increases and lipid inclusions form. LH, interacting with protein receptors of granulosa cells, stimulates the process of their luteinization. This process leads to the formation of the corpus luteum.

The corpus luteum is a transient endocrine gland that functions for 14 days, regardless of the duration of the menstrual cycle. In the absence of pregnancy, the corpus luteum regresses.

Thus, the main female sex steroid hormones - estradiol and progesterone, as well as androgens are synthesized in the ovary.

In phase I of the menstrual cycle, which lasts from the first day of menstruation until the moment of ovulation, the body is under the influence of estrogens, and in phase II (from ovulation to the beginning of menstruation), progesterone, secreted by the cells of the corpus luteum, joins estrogens. The first phase of the menstrual cycle is also called follicular, or follicular, the second phase of the cycle is luteal.

During the menstrual cycle, two peaks of estradiol content are observed in the peripheral blood: the first, a pronounced preovulatory cycle, and the second, less pronounced, in the middle of the second phase of the menstrual cycle. After ovulation, in the second phase of the cycle, the main hormone is progesterone, the maximum amount of which is synthesized on the 4-7th day after ovulation (Fig. 2.13).

The cyclic secretion of hormones in the ovary determines changes in the uterine mucosa.

Cyclic changes in the uterine mucosa (endometrium). The endometrium consists of the following layers.

1. The basal layer, which is not torn off during menstruation. During the menstrual cycle, its cells form the endometrial layer.

2. The superficial layer, consisting of compact epithelial cells that line the uterine cavity.

3. Intermediate, or spongy, layer.

The last two layers constitute the functional layer, which undergoes major cyclic changes during the menstrual cycle and is shed during menstruation.

In phase I of the menstrual cycle, the endometrium is a thin layer consisting of glands and stroma. The following main phases of changes in the endometrium during the cycle are distinguished:

1) proliferation phase;

2) secretion phase;

3) menstruation.

Proliferation phase. As the secretion of estradiol by growing ovarian follicles increases, the endometrium undergoes proliferative changes. There is an active proliferation of cells in the basal layer. A new superficial loose layer with elongated tubular glands is formed. This layer quickly thickens 4-5 times. Tubular glands, lined with columnar epithelium, elongate.

Secretion phase. In the luteal phase of the ovarian cycle, under the influence of progesterone, the tortuosity of the glands increases, and their lumen gradually expands. The stromal cells, increasing in volume, move closer to each other. The secretion of the glands increases. A copious amount of secretion is found in the lumen of the glands. Depending on the intensity of secretion, the glands either remain highly convoluted or take on a sawtooth shape. There is increased vascularization of the stroma. There are early, middle and late phases of secretion.

Menstruation. This is the rejection of the functional layer of the endometrium. The subtle mechanisms underlying the occurrence and process of menstruation are unknown. It has been established that the endocrine basis for the onset of menstruation is a pronounced decrease in the levels of progesterone and estradiol due to regression of the corpus luteum.

There are the following main local mechanisms involved in menstruation:

1) change in the tone of spiral arterioles;

2) changes in the mechanisms of hemostasis in the uterus;

3) changes in the lysosomal function of endometrial cells;

4) endometrial regeneration.

It has been established that the onset of menstruation is preceded by intense narrowing of the spiral arterioles, leading to ischemia and desquamation of the endometrium.

During the menstrual cycle, the content of lysosomes in endometrial cells changes. Lysosomes contain enzymes, some of which are involved in the synthesis of prostaglandins. In response to a decrease in progesterone levels, the release of these enzymes increases.

Regeneration of the endometrium is observed from the very beginning of menstruation. By the end of the 24th hour of menstruation, 2/3 of the functional layer of the endometrium is rejected. The basal layer contains epithelial stromal cells, which are the basis for endometrial regeneration, which is usually completely completed by the 5th day of the cycle. In parallel, angiogenesis is completed with the restoration of the integrity of ruptured arterioles, veins and capillaries.

Changes in the ovaries and uterus occur under the influence of the two-phase activity of the systems regulating menstrual function: the cerebral cortex, the hypothalamus, the pituitary gland. Thus, there are 5 main links in the female reproductive system: cerebral cortex, hypothalamus, pituitary gland, ovary, uterus (Fig. 2.14). The interconnection of all parts of the reproductive system is ensured by the presence in them of receptors for both sex and gonadotropic hormones.

The role of the central nervous system in regulating the function of the reproductive system has been known for a long time. This was evidenced by ovulation disturbances under various acute and chronic stress, menstrual cycle disturbances due to changes in climatic and geographical zones and work rhythm; The cessation of menstruation in wartime conditions is well known. In mentally unstable women who passionately desire to have a child, menstruation may also stop.

In the cerebral cortex and in extrahypothalamic cerebral structures (limbic system, hippocampus, amygdala, etc.), specific receptors for estrogens, progesterone and androgens have been identified. In these structures, the synthesis, release and metabolism of neuropeptides, neurotransmitters and their receptors occur, which in turn selectively influence the synthesis and release of hypothalamic releasing hormone.

The following neurotransmitters function in conjunction with sex steroids: norepinephrine, dopamine, gamma-aminobutyric acid, acetylcholine, serotonin and melatonin. Norepinephrine stimulates the release of gonadotropin-releasing hormone (GTRH) from neurons in the anterior hypothalamus. Dopamine and serotonin reduce the frequency and amplitude of GTRH production during various phases of the menstrual cycle.

Neuropeptides (endogenous opioid peptides, neuropeptide Y, corticotropin-releasing factor and galanin) also influence the function of the reproductive system, and therefore the function of the hypothalamus. Endogenous opioid peptides of three types (endorphins, enkephalins and dynorphins) are able to bind to opiate receptors in the brain. Endogenous opioid peptides (EOPs) modulate the effect of sex hormones on the content of GTRH through a feedback mechanism, block the pituitary gland's secretion of gonadotropic hormones, especially LH, by blocking the secretion of GTRH in the hypothalamus.

The interaction of neurotransmitters and neuropeptides ensures regular ovulatory cycles in the body of a woman of reproductive age, influencing the synthesis and release of GTRH by the hypothalamus.

The hypothalamus contains peptidergic neuron cells that secrete stimulating (liberins) and blocking (statins) neurohormones - neurosecretion. These cells have the properties of both neurons and endocrine cells, and respond to both signals (hormones) coming from the bloodstream and neurotransmitters and neuropeptides from the brain. Neurohormones are synthesized in the ribosomes of the neuron cytoplasm and then transported along the axons to the terminals.

Gonadotropin-releasing hormone (liberin) is a neurohormone that regulates the gonadotropic function of the pituitary gland, where FSH and LH are synthesized. LH releasing hormone (Luliberin) has been isolated, synthesized and described in detail. To date, it has not been possible to isolate and synthesize follicle-stimulating hormone, or folliberin.

GnRH secretion has a pulsating nature: peaks of enhanced hormone secretion lasting several minutes are replaced by 1-3 hour intervals of relatively low secretory activity. The frequency and amplitude of GnRH secretion is regulated by estrogen levels.

The neurohormone that controls the secretion of prolactin by the adenohypophysis is called prolactin-inhibiting hormone (factor), or dopamine.

An important link in the reproductive system is the anterior lobe of the pituitary gland - the adenohypophysis, which secretes gonadotropic hormones, follicle-stimulating hormone (FSH, follitropin), luteinizing hormone (LH, lutropin) and prolactin (Prl), which regulate the function of the ovaries and mammary glands. All three hormones are protein substances (polypeptides). The target gland of gonadotropic hormones is the ovary.

The anterior lobe of the pituitary gland also synthesizes thyroid-stimulating (TSH) and adrenocorticotropic (ACTH) hormones, as well as growth hormone.

FSH stimulates the growth and maturation of ovarian follicles, promotes the formation of FSH and LH receptors on the surface of ovarian granulosa cells, increases the content of aromatase in the ripening follicle and, by stimulating aromatization processes, promotes the conversion of androgens into estrogens, stimulates the production of inhibin, activin and insulin-like growth factor-1, which play an inhibitory and stimulating role in follicle growth.

LG stimulates:

Formation of androgens in theca cells;

Ovulation together with FSH;

Remodeling of granulosa cells during luteinization;

Synthesis of progesterone in the corpus luteum.

Prolactin stimulates mammary gland growth and lactation, controls the secretion of progesterone by the corpus luteum by activating the formation of LH receptors in them.

Rice. 2.14.

RHLH - releasing hormones; OK - oxytocin; Prl - prolactin; FSH - follicle-stimulating hormone; P - progesterone; E - estrogens; A - androgens; R - relaxin; I - inhibin; LH - luteinizing hormone.

Rice. 2.15.

I - gonadotropic regulation of ovarian function: PDH - anterior lobe of the pituitary gland, other symbols are the same as in Fig. 2.14; II - content in the endometrium of receptors for estradiol - RE (1,2,3; solid line) and progesterone - RP (2,4,6; dotted line); III - cyclical changes in the endometrium; IV - cytology of the vaginal epithelium; V - basal temperature; VI - tension of cervical mucus.

The synthesis of prolactin by the adenohypophysis is under the tonic blocking control of dopamine, or prolactin-inhibiting factor. Inhibition of prolactin synthesis ceases during pregnancy and lactation. The main stimulator of prolactin synthesis is thyrotropin-releasing hormone, synthesized in the hypothalamus.

Cyclic changes in the hypothalamic-pituitary system and in the ovaries are interconnected and modeled as feedback.

The following types of feedback are distinguished:

1) a “long loop” of feedback - between ovarian hormones and the nuclei of the hypothalamus; between ovarian hormones and pituitary gland;

2) “short loop” - between the anterior lobe of the pituitary gland and the hypothalamus;

3) “ultra-short loop” - between the GTRG and the nerve cells of the hypothalamus.

The relationship of all these structures is determined by the presence of receptors for sex hormones in them.

A woman of reproductive age has both negative and positive feedback between the ovaries and the hypothalamic-pituitary system. An example of negative feedback is the increased release of LH by the anterior pituitary gland in response to low estradiol levels during the early follicular phase of the cycle. An example of positive feedback is the release of LH in response to the ovulatory maximum of estradiol in the blood.

The state of the reproductive system can be judged by assessing functional diagnostic tests: basal temperature, pupil symptom and karyopyknotic index (Fig. 2.15).

Basal temperature is measured in the rectum in the morning, before getting out of bed. During the ovulatory menstrual cycle, the basal temperature rises in the luteal phase of the cycle by 0.4-0.6 °C and remains the same throughout the second phase (Fig. 2.16). On the day of menstruation or the day before it, the basal temperature decreases. During pregnancy, an increase in basal temperature is explained by excitation of the thermoregulatory center of the hypothalamus under the influence of progesterone.

. Menstrual cycle- this is a set of morphological and physiological changes in a woman’s body from one menstruation to the next menarche (first menstruation) manifests itself during puberty, mainly at the age of 12-14 years, sometimes much earlier (at 9-10 years) or later (15-16 years). Regardless of nationality, the average duration of the menstrual cycle (from the first day of the previous to the first day of the next menstruation) is 75% of cases 28 days, which corresponds to one month according to the lunar calendar.

After 45 years of life, the regularity of menstrual cycles is disrupted, and then they completely disappear, that is, menopause begins

The regulation of the menstrual cycle is carried out by the hypothalamus, pituitary gland and ovaries. The generator of the menstrual cycle is the ovaries, which is why they are often called the “timer” - the “biological clock” of the cycle.

During the menstrual cycle, processes occur in the ovary (ovarian cycle, has follicular and luteal phases) and in the uterus (uterine cycle, which is divided into menstrual, proliferative and secretory phases.

. Ovarian cycle(changes in the ovary)

. Follicular phase. Influenced. FSH begins to develop several (up to 15) primary follicles containing first-order oocytes. One follicle between them begins to dominate from the 7th day of the menstrual cycle, the remaining follicles degenerate (the phenomenon of atresia). In the dominant follicle, the diameter of which reaches 20-28 mm, follicular cells multiply and, thanks to the influence of luteinizing hormone, they synthesize estrogens (there are 13,000 times more of them in the follicular fluid than in the blood). A significant increase in the amount of estrogen ensures hyperplasia of the uterine mucosa, an increase in the pH of the upper part of the vagina, the spread of the cervical canal, and a thinning of its mucus.

An increase in estrogen in the blood is a prerequisite for ovulation; in addition, during days 4 to 11 of the cycle they cause a decrease in the level of follicle-stimulating hormone, but do not affect the amount of luteinizing hormone. The level of estrogen in the blood reaches its maximum value three days before ovulation, it is at this time that they stimulate the synthesis of both gonadotropic hormones of the pituitary gland. This positive relationship between the synthesis of estrogen and luteinizing hormone is characteristic only in the pre-vulation period (E Knobil, 1972-72).

luteal phase. In the mature follicle, which is also called the Graafian vesicle, the first meiotic division occurs, thanks to which the first-order oocytes arise from the second-order oocytes. After rupture of the follicle wall (nulation, which occurs mainly on the 14th day of the cycle), the oocytes, surrounded by a layer of cells, enter the fallopian tube in the abdominal cavity. At this time, it contains a haploid set of chromosomes (22 somatic and 1 Tatev, but each has 2 DNA molecules). The formation of the actual mature egg will occur only when the oocyte completes the second meiotic division, namely during the penetration of sperm into it. After this, the male and female gametes (from gamete - wife and gametes - man) merge and a zygote is formed (from zigotos - united together).

After ovulation, the level of luteinizing hormone decreases, and in place of the ruptured follicle, under the influence of prolactin, a corpus luteum is formed. It, like the dominant follicle, becomes the main structure of the ovary, inhibits the growth and development of other follicles, and produces predominantly progesterone rather than estrogens. Progesterone inhibits the synthesis of gonadotropins and maintains the state of readiness of the uterine mucosa for interruptions in pregnancy. The most favorable conditions for the uterus to receive a zygote are created on the 7th day after ovulation. If fertilization does not occur, then the second-order oocytes die in the oviduct, the corpus luteum is still preserved for 10-14 days, but it decreases and a small scar remains. A decrease in progesterone synthesis by feedback principle causes more production of follicular hormone, so a new cycle begins, and the luteal phase of menstruation ends with an end.

If the zygote has arisen and established itself in the uterus, that is, during pregnancy, the corpus luteum continues to grow, reaching a diameter of 2-3 cm. The functioning of the corpus luteum is supported by the chorionic hormone, which is ingested by the placenta and is similar in activity to luteinizing hormonal hormone.

The influence of progesterone on the thermoregulation center leads to cyclical fluctuations in the internal body temperature of women. So, during the luteal phase the temperature increases by 0.6-0.8 °. With higher than during follicular growth, growth begins 1-2 days after ovulation, when the corpus luteum is formed, the cells of which synthesize progesterone.

uterine cycle(changes in the uterus)

. Menstrual phase. Occurs due to a decrease in the level of ovarian hormones (estrogens and progesterone), so there is a narrowing of blood vessels, a deterioration in the blood supply to the uterine mucosa, its epithelial layer dies and is left without nutrients. Then the vessels dilate, more blood flows in, and dead cells are removed with it due to the increased intensity of contraction of the muscles of the uterus.

. Proliferative phase. The time coincides with the follicular phase of the ovarian cycle, as it is associated with the influence of estrogen. There is an intensive proliferation of cells of the mucous membrane, which thickens significantly, and an acidic secretion with pH = 4.5 -5 is formed.

Secretory phase. It coincides in time with the luteal phase of the ovarian cycle. Under the influence of progesterone, the tubular glands of the uterine mucosa grow and produce a lot of mucus.

Menstruation lasts 3-5 days, it actually completes the female sexual cycle, but traditionally the cycle begins from it

. Sexual behavior is a complex of complex physiological, psychological and behavioral reactions associated with sexual function. Almost all human organ systems are involved in its manifestation. Sexual intercourse is an element of the natural cycle - this is actually copulation (coitus), this is a duet of two equal people united by love. Over many centuries, a far-fetched idea has been established in European and Christian civilization; in this cycle, it is only the insertion of the penis into the vagina and related the actions of reality are not so. For sexual lovers, there is everything that unites them, namely being together, sleeping, relaxing, reading, visiting cultural institutions, etc.

3. Freud considered sexual relations to be the main motivating factor in all aspects of human behavior. One of the most important achievements of Z. Freud is the creation of the theory of human psychosexual development. He believed that the main cause of all neuroses is a psychological disorder based on sexual relationships, so he created the method of psychoanalysis to treat them.

In human sexual life, an important role is played by erogenous zones - areas of the skin and mucous membranes, the irritation of which causes sexual arousal or enhances it. They are divided into genital, those associated with the genitals, and extragenital (oral mucosa, lips, tongue, skin of the buttocks, inner edge of the sole, inner thigh, earlobe, etc.). Men are characterized by a suppressive but genital zone, and in women both groups are common.

In men and women, the sexual cycle includes four phases, which change sequentially with each other. The first phase is an increase in sexual arousal, the second is maintaining sexual arousal at the same level (plateau), the third is orgasm, the fourth is relaxation.

These phases manifest themselves differently in different people, which is due to their individual characteristics, but the physiological manifestation of the sexual reaction is more expressive in women. Women, as a rule, are more sexual than men, since they have a larger number of erogenous zones, especially extragenital ones.

Orgasm (from o ^ is sexual intercourse, but only 30% of women regularly enjoy orgasm. In men, orgasm is achieved through ejaculation.

It is believed that as a result of sexual intercourse, the brain intensively produces endorphins and enkephalins (endogenous opioids), which have narcotic properties, like opium and morphine, so they play a vital role in human behavior and are able to influence the vegetative processes of the body.

The combination of love and pleasure makes sex an important activity in the fight against stress and its destructive power on the heart, circulation, and immune system.

Sex is often called the quintessence of all human feelings, relationships, moods, desires. This is a way of mutual enrichment of partners, when each makes the other feel what is pleasant to him and what is not.

The main biological purpose of human sexuality, in addition to self-realization, is the birth of children. The reproductive system of women significantly influences the aging process of their body

American sexologist. D. Bancroft believes that one of the most important functions of human sexuality (except reproductive) is the preservation of the family, because sexual satisfaction reinforces the desire to stay together and creates a reliable emotional background. Starting a family and maintaining it is not only great happiness, but also great art.

Libido is the mental energy of sexual desire, which is associated with love

According to dualistic theory. Freud, a person has two basic instincts - to life (eros) and to death (ta-natos). Libido, as an expression of erotic energy, resists the destructive force of the desire for death, sexual desire is an integral part of the human personality.

Phases of libido formation:

1) conceptual, when while playing gender-role games, children realize the existence of differences between people of different sexes;

2) romantic, when fantasies arise, desires to please others;

3) erotic, when interest arises in everything related to sexual relations;

4) sexual, when there is a desire for sexual relations with a partner

The main stimulator of male potency and female orgasm is infatuation or love (classical love. Aloisi do. ​​Abelard). Love and human sexuality are integral, they belong to the highest level of human needs, as they provide the opportunity to achieve the flourishing of personality, at the height of self-realization. Students. Socrates, followers of hedonism (pleasure), believed that the goal of every person’s life is to achieve pleasure and avoid dissatisfaction, and happiness consists of the sum of the pleasures experienced. Extremely great love. Tennov called limerincia, it is influenced by the mediator serotonin (after Leibovich).

The direction of sexual desire is associated with several levels of human gender formation, which depend on such factors;

Genetic - from the presence of a pair of sex chromosomes (XX or xy);

Gonadal - from the presence of gonads that form the corresponding gametes (ovaries or testes);

Hormonal - from the formation and ratio of sex hormones (estrogens or androgens) in the blood;

Morphological - from the anatomical structure of individual organs and parts of the body (the severity of primary and secondary sexual characteristics);

Psychological - from upbringing and understanding by the person in her environment of her belonging to a certain gender

The consequence of the gradual formation of sexual desire is the conscious choice of a sexual partner and appropriate behavior in sexual relations

To the works of 3. Freud, it was believed that sexuality is inherent in children. Later, an ultrasound examination showed that an eight-month-old fetus has an erection.

3. Freud identifies three stages of pregenital sexuality in children. In each phase, one organ or function comes to the fore;

1) first phase and oral component;

2) second phase and anal component;

3) third phase and phallic component, i.e. increased interest in genitals, masturbation

Sexological manifestations of each person go through certain periods of development

1 parapubertal (from para - nearby, pubertas - puberty) - formation at the age of 1 - 7 years of self-awareness of one's gender, children's interest in the sexual sphere

2. Prepubertal (from prae - before, pubertas - puberty) - creation at the age of 7-13 years of a stereotype of future gender-role behavior

3. Puberty (from pubertas - sexual maturity) - awakening of libido at the age of 12-18 years, the desire to assert oneself, including sexually

4. Transitional - the beginning of sexual life at the age of 16-26, but not uniform relationships over time

5 mature sexuality - achievement at the age of 26-55 years of stable sexual activity characteristic of the constitution of a particular person

6. Involutional - after 50 years, gradual loss of interest in sexual relations, decreased sexual activity

Psychosexual orientation, a person’s awareness of his belonging to a certain gender, can manifest itself in the form of hetero-, bi- and homosexuality, and other forms of sexual behavior

heterosexuality(from heteros - other, sexualis - sexual) - this is a sexual desire for an individual of a different sex. The basis of heterosexuality is love

. Bisexuality(from bis - twice, sexualis - sexual) - the presence of sexual desire for individuals of both their own and the other sex

. Homosexuality(from homos - equal, identical, sexualis - sexual) - this is sexual orientation towards a partner of the same sex. According to the data. A. Kinsey, 2-3% of women and almost 4% of men are homosexuals

. Erotica(from erotikos - love) - all aspects of communication, culture and art that reflect sexual desire in a form acceptable to the majority of members of society

. Pornography(from pornos - libertine, grapho - writing) - this is a description of the genitals, sexual intercourse in literature or art with the aim of achieving sexual pleasure, but in a form that is unacceptable for the majority of members in societies.

. Monogamy(from monos - one, gamos - marriage) and polygamy (from polys - many, gamos - marriage). A large number of germ cells should incline men to polygamy in order to make it possible to pass on their genes to the maxim of the minimum number of descendants, and the maturation of only one egg in women in 28 days inclines the woman to monogamy. Therefore, in a monogamous marriage, a man cannot always satisfy his sexual needs, but a woman’s sexuality and her sexual perception does not depend on the reproductive cycle, so this discrepancy may disappear. Primates, except gibbons, are polygamous; only the female gibbon is also capable of sexual activity, regardless of the reproductive cycle.

In persons with an accentuated character, the manifestation of sexuality is also different. For example, a schizoid type is outwardly contemptuous of the sexual sphere, he is often unable to attract the attention of the opposite sex to himself by ordinary means, this causes him to have a tendency to peek or show others his genitals.

Inertia in the behavior of the epileptoid type leads to the fact that they are very afraid of infection from new partners, they are characterized by jealousy even towards flirting, they consider any reaction of their partner to attention from others to be treason, they are sadomasochistic.

The period of puberty is characterized by a pronounced change in the hierarchy of needs, the need for self-respect, approval, recognition arises, aesthetic needs, desires for self-affirmation and self-realization are formed.

Changes in sexual behavior and the onset of sexual activity require a change in the social status of a young person, her joining adults, independence from parents

Having sex too early is socially and psychologically harmful to the further development of adolescents

Erikson (1968) believes that the main task of youth is to develop the ability and skills of sexual relations. It should be noted that they depend on intelligence, character

Masters and. Johnson (doctors, scientists, spouses) - authors of the books "Human Sexual Response", "Human Sexual Inadequacy" (1966,1970), "Masters and Johnson on Love and Sex" (1982), have done a lot about what sexual relationships have become more understandable to all people. They described several types of sexual behavior and several types of sexual behavior:

- “experimenters” who strive to increase the number of sexual partners; for them the whole world is a large sexual testing ground;

- “seekers” who use any means in search of an ideal; they increase the number of sexual partners in order to find the greatest pleasure;

- “conservatives” who are very picky about sex, they willingly flirt, but do not bring the matter to sexual intercourse

In a consumer society there is a lot of sex, but little love, especially mutual love. Sexual activity without marriage is spreading too quickly these days.

Even from a fugitive review of cyclical changes various parts of the female reproductive apparatus, it is clearly visible that all periodic phenomena must be coordinated to a certain extent with each other. Each organ plays its role in reproduction. It is not enough that he periodically perform this role with maximum efficiency; the period of readiness of each organ or its part should occur when the entire complex mechanism of reproduction is ready to function.

For a long time now with certainty installed that hormones control and coordinate in time the various stages of the reproductive cycle. The interaction of these hormones is very complex. Long and persistent experimental work was required to clarify the results obtained under the influence of any one hormone. A much more difficult task is to interpret the results of the influence of several hormones acting together or sequentially.

Currently in biology There is no area where research is as intense as in endocrinology. Almost every biological or medical journal adds to our information about the methods of formation, chemical properties or physiological action of hormones. Nevertheless, it is still impossible to give at least a brief approximate outline of some of the most important hormones that regulate the sexual cycle, without the caveat that most of the data was obtained recently, has not yet been thoroughly verified, and therefore a clear idea of ​​the subject will only emerge in the future.

It is paradoxical that the primary activator of the sexual process- the pituitary gland is not located near the reproductive organs, but is located deep in the skull, in close connection with the brain. The pituitary gland, slightly larger in size than a cherry pit, is an inconspicuous mass of tissue, but its action has long aroused human curiosity. In the Middle Ages, scientists debated whether the pituitary gland was the permanent seat of the soul or a special organ that secreted mucus from the brain.
It has now been established that pituitary at different times produces from 5 to 15 hormones, most of which are known under several names.

Long before puberty maturity The anterior lobe of the pituitary gland, through one of the hormones it produces, begins to influence the development of the genital organs. In young hypophysectomized animals, the reproductive organs remain underdeveloped, the characteristic sexual cycle is not established, and the individual turns out to be sterile. Although it has long been known that when the ovaries are removed early, the menstrual cycle is not observed at all and that their removal at puberty leads to the cessation of menstruation, but only now we have begun to understand that the reasons for these changes lie much deeper. Even before the ovary begins to activate the uterus, it must first come to a state of functional activity under the influence of the stimulating effects exerted on it during the period of its growth by the hormone of the anterior pituitary gland.

This is action pituitary gland is only the beginning of a whole series of processes. After reaching puberty, the pituitary gland begins to produce hormones that have a profound effect on the gonads and are therefore called gonadotropic hormones, in contrast to other hormones of pituitary origin that act on other organs, such as thyroid-stimulating and adrenocorticotropic hormones. It is currently believed that there are two gonadotropic hormones, one of which stimulates the development of the follicle, and the second - the development of the corpus luteum.

Hormone, stimulating follicular development, activates their consistent growth and maturation. Here another link in the chain of hormonal action arises: when the follicles enlarge, they begin to produce a hormone that can be obtained from the follicular fluid. This hormone is estradiol. Injection of the required amount of estradiol into experimental animals that had not experienced estrous changes due to complete ovariectomy resulted in the restoration of typical estrus symptoms.

On this basis estradiol often called estrogen hormone. The importance of estradiol, the amount of which increases significantly at the time of ovulation, is quite obvious. The maximum amount of this hormone, which stimulates sexual activity, is observed in the period preceding the release of the egg from the follicle into the abdominal cavity.

Following ovulation, another group is activated hormones. A hormone from the anterior pituitary gland that stimulates the development of the corpus luteum causes rapid proliferation of epithelial cells of the ruptured follicle. At the same time, the chemical properties of these cells change, which is associated with the formation of the corpus luteum. In turn, the corpus luteum, under the influence of additional stimulation from the lactogenic hormone, produces a hormone that acts on the uterus. This hormone, called progesterone, causes the lining of the uterus to change to prepare it for pregnancy.

Here again it is obvious stands clear consistency in time, because the chain of processes that leads to the preparation of the uterus for the reception of the embryo begins during the first stages of development of the egg.

With such sequences phenomena, the connection between ovulation and menstruation takes on special significance. If ovulation takes place, say, on the 13th day of the menstrual cycle, and sexual intercourse occurs around the same time, this allows the embryo to develop for 7 days, which contributes to its successful implantation into the already prepared uterine mucosa. During these 7 days, under the influence of the corpus luteum hormone, the uterine mucosa thickens, its glands become active, and the amount of blood in it increases. When the uterus is in this premenstrual phase, it is already ideally prepared to receive and strengthen the embryo.

It turned out that corpus luteum hormone in addition to its effect on the uterus, it has another, no less important physiological effect. Injection of corpus luteum extract has been repeatedly shown to delay ovulation. This action is determined by the relationship in time between the maximum development of the corpus luteum of ovulation and other phenomena of the cycle. The corpus luteum reaches a noticeable stage of development and acquires histological signs of active secretion a few days after the rupture of the follicle from which it was formed.

When examined microscopically one can see that regressive changes in the corpus luteum appear when the next menstrual period is about to begin, and the corpus luteum reaches a noticeable reduction in size by the time the new follicle matures. These findings indicated that the ovulating corpus luteum is a source of a hormone that acts as an antagonist of pituitary follicle-stimulating hormone, causing a delay in the development of subsequent follicles.

Phenomena of the reproductive cycle were presented in the simplest form, without unnecessary detail, of a number of facts that make these phenomena one of the most fascinating areas of modern biological science. However, even this short sketch demonstrates how amazingly coordinated the entire mechanism of reproduction is. So far we have only seen a series of changes that are repeated in preparation for pregnancy. Ovulation is a critical phenomenon to which all other cyclic changes occur. The egg released when the follicle ruptures is ready for fertilization and all other organs are also ready to play their role if the egg is fertilized.