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Ovary (ovarium, oophorori)- a paired organ of the female reproductive system and at the same time an endocrine gland (Fig. 1).
The mass of the ovary normally does not exceed 5-8 g, the dimensions are 2.5-5.5 cm in length, 1.5-3.0 cm in width and up to 2 cm in thickness.
The ovary consists of two layers: the cortical substance, covered with a protein membrane, and the medulla. The cortical substance is formed by follicles of varying degrees of maturity.
Rice. 1. Ovary: processes occurring during the ovulatory cycle
Main steroid hormones secreted by the ovaries are estrogen and progesterone, as well as airogens. Estrogens are estradiol, estrone and estriol. Estradiol(E2) is secreted predominantly by granulosa cells. Estrone (E1) is formed by peripheral aromatization of estradiol; estriol (E3) is synthesized by the ovaries in trace amounts; the main source of estriol is the hydroxylation of estradiol and estrone in the liver.
The main progestogenic hormone (progestin) is progesterone, which is secreted mainly by the corpus luteum. The main ovarian androgen secreted by theca cells is androstenedione. Normally, most of the androgens in the female body are of adrenal origin. The starting compounds for the synthesis of estrogens and progesterone is cholesterol. The biosynthesis of sex hormones occurs similarly to the biosynthesis of corticosteroids. Steroid hormones of the ovaries, like those of the adrenal glands, practically do not accumulate in the cells, but are secreted in the process of synthesis.
In the bloodstream, a significant part of the steroids binds to transport proteins: estrogens - with sex hormone-binding globulin (SHBG), progesterone - with cortisol-binding globulin (transcortin). The mechanism of action of estrogens, progestins and androgens is similar to that of other steroid hormones.
The main estrogen metabolites are catecholestrogens (2-hydroxyestrone, 2-methoxyestrone, 17-epistriol), which have weak estrogenic activity; The main metabolite of progesterone is pregnandiol.
Before the onset of puberty, gonadotropin-independent, very slow growth of primary follicles occurs in the ovaries. Further development of mature follicles is possible only under the influence of pituitary hormones: follicle-stimulating(FSH) and luteinizing(LH), the production of which, in turn, is regulated by gonadoliberin of the hypothalamus. IN ovarian cycle two phases are distinguished - follicular and luteal, which are separated by two events - ovulation and menstruation (Fig. 2).
Rice. 2. Cyclic changes in the reproductive system of a woman during the menstrual cycle
IN follicular phase secretion of FSH by the pituitary gland stimulates the growth and development of primary follicles, as well as the production of estrogens by follicular epithelial cells. Preovulatory release of gonadotropins determines the process of ovulation. The ovulatory release of LH and, to a lesser extent, FSH is due to pituitary sensitization to the action of GnRH and is associated with a sharp drop in estradiol levels during the 24 hours preceding ovulation, as well as with the existence of a positive feedback mechanism of ultra-high concentrations of estrogens and LH levels.
Under the influence of an ovulatory increase in LH levels, the formation of the corpus luteum occurs, which begins to produce progesterone. The latter inhibits the growth and development of new follicles, and is also involved in the preparation of the endometrium for the introduction of a fertilized egg. The plateau of the serum concentration of progesterone corresponds to the plateau of the rectal (basal) temperature (37.2-37.5 ° C), which underlies one of the methods for diagnosing ovulation that has occurred. If further fertilization does not occur, after 10-12 days regression of the corpus luteum occurs, if the fertilized egg has invaded the endometrium and the resulting blastula began to synthesize chorionic gonadotropin (CG), the corpus luteum becomes the corpus luteum of pregnancy.
The duration of the ovarian (menstrual) cycle normally varies from 21 to 35 days. The most common is the 28-day cycle, which exists for a long time only in 30-40% of women. There are three periods or phases in the menstrual cycle: menstrual (endometrial desquamation phase), which ends the previous cycle, postmenstrual (endometrial proliferation phase), premenstrual (functional, or secretory phase). The boundary between the last two phases is ovulation. The countdown of the days of the menstrual cycle starts from the first day of menstruation.
Dedov I.I., Melnichenko G.A., Fadeev V.F.
Endocrinology
Women's the reproductive system is formed by the external and internal genital organs and is characterized by primary and secondary female characteristics.
External female genital organs form large labia, labia minora, clitoris, hymen, bartholin glands, mammary glands.
Large labia are two skin folds containing fat. At the top, they pass into the pubis, covered with small curly hair, and at the bottom they are connected, forming the posterior commissure of the vagina. The space between the posterior commissure of the vagina and the anus (anus) is called the perineum.
The slit-like formation between the labia majora is called the genital slit. In women who have not given birth, the large labia are closed, and in those who have given birth, they diverge somewhat, slightly opening the small labia. Function of the labia majora: protection of the labia minora from the damaging effects of external harmful factors, an obstacle to the penetration of air, water and dust into the vagina; sexy.
Small labia are located medially from the labia majora and are usually completely hidden between them. They are two longitudinal folds of skin, resembling a mucous membrane in appearance. The labia minora are very sensitive to external stimuli. In their thickness are fibers of connective and muscle tissue, blood vessels, endings of sensory nerves, as well as glands. The labia minora at the top cover the clitoris, and at the bottom they merge with the inner surface of the labia majora. The slit-like opening between the labia minora is called vestibule. The urethra, vagina and ducts of the glands of the vestibule open into it. The function of the labia minora: protective and sexy. Small labia cover the entrance to the vagina and prevent the penetration of water, dust, air into it. With sexual arousal, they become thicker due to blood filling, and the sensitivity of their erogenous zones increases. When the penis is inserted into the vagina, the labia minora covers it, which contributes to irritation of the erogenous zones, increased sexual arousal and orgasm.
Clitoris(from lat. - clitoris) - a cone-shaped formation located in the upper corner of the genital slit. In its structure, the clitoris is similar to the male genital organ. His growth ends by the age of 25. In a calm state, the length and thickness of the clitoris usually fluctuates within a few millimeters. With sexual arousal, the clitoris becomes dense, and its size increases several times due to blood filling. There are 3-4 times more sensitive nerve endings on the clitoris than on the penis.
Function of the clitoris: The clitoris has a sexual function. In 50-60% of women, the main erogenous zones are located on the clitoris.
Hymen(from Latin - hymen femininus) is located on the border between the labia minora and the vagina and represents the bottom of the vestibule of the vagina. The hymen is formed by a fold of the vaginal mucosa and consists of loose connective tissue with a large number of elastic fibers, blood vessels and nerve endings. There are about 20 varieties of hymen with one or more holes. At the first sexual intercourse, a rupture of the hymen (defloration) occurs with moderate pain and slight bleeding. The function of the hymen is little understood. It is believed that the girl's hymen performs a barrier function, preventing the penetration of pathogenic microbes, air, dust and water into the vagina. After puberty, this barrier function is performed by the large and small labia, covering the entrance to the vagina.
bartholin glands They are oval in shape and are located one on each side of the vagina. Their opening is located in the groove between the hymen and the root of the labia minora.
Function of the Bartholin glands: When sexually aroused, women secrete mucus that moistens the vestibule of the vagina. This contributes to the free and painless introduction of the penis into the vagina.
The internal female reproductive organs are formed by the ovaries, fallopian tubes, uterus and vagina. These organs are located in the pelvis.
ovaries(from lat. ovarium), or female gonads, are paired organs located in the pelvis to the left and right of the uterus. They have an oval shape measuring 2.5 x 1.5 x 1.0 cm. The ovaries in the embryo develop into abdominal cavity, then gradually descend into the pelvic cavity and remain in it throughout the life of a woman. With the onset of puberty, Graafian vesicles form in the ovaries of the girl, in which the female germ cell (egg, or ovum) grows and matures. At the same time, one or more follicles can appear in one or two ovaries. This explains the birth of one, two or more twin children. Children born from two independent eggs are called fraternal twins, from three eggs - three-egg, etc. Twins born from the same egg are called identical twins, which are very similar in physical, biochemical, mental and other indicators.
Functions of the ovaries: the formation and development of female germ cells; synthesis and secretion of two types of female sex hormones (estrogen, progesterone), which ensure growth and development female body; the synthesis and secretion of a small amount of the male sex hormone (testosterone), which causes a woman's sexual arousal (libido). In place of the bursting follicle, a new gonad is formed, called the corpus luteum. It secretes a hormone that ensures the preservation and development of pregnancy. If pregnancy does not occur, then the corpus luteum dissolves, and a scar forms in its place.
The uterine or fallopian tubes- paired organ. Depart to the left and right of the corner of the bottom of the uterus. Their length is 10-12 cm, diameter is about 2-3 mm. The outer end of the fallopian tube has the appearance of a funnel with numerous fringes that are in contact with the ovaries. The wall of the fallopian tube consists of three membranes: serous, muscular and mucous. The mucous membrane is covered with a cylindrical ciliated epithelium, the cilia of which fluctuate towards the uterus. The abdominal cavity of a woman through the lumen of the fallopian tubes, the uterine cavity, the cervical canal of the cervix and the vagina communicates with the external environment.
Functions of the fallopian tubes: Due to vibrations of the cilia of the epithelium and contractions of the muscle fibers of the fallopian tube, the egg, captured by the fimbriae, moves from the abdominal cavity to the uterus, and the spermatozoon, due to vibrations of the tail, moves from the uterus to the fallopian tube and abdominal cavity. As a rule, in the fallopian tube, the male and female germ cells merge to form a zygote (fertilization).
Uterus pear-shaped, located in the pelvis between the bladder in front and the rectum in the back. Its length is 6-9 cm. In the uterus, the bottom, body and neck are distinguished. The cervix protrudes into the upper part of the vagina and has a canal called the cervical canal or cervical canal. One end of the cervical canal opens into the uterine cavity, the other into the vagina. The cervical canal is filled with mucus, which prevents the infection from entering the uterine cavity. The uterine cavity has the form of a triangle with the base to the bottom of the uterus. At each corner of the base of the uterus is the mouth of the fallopian tube. The wall of the uterus has three layers: outer, middle, inner. The outer layer is formed by the peritoneal cover, the middle myometrium- smooth muscle fibers with a longitudinal and annular arrangement. During pregnancy, the muscular layer of the uterus increases, which allows during childbirth to develop significant force to expel the fetus and placenta. After childbirth, the muscular layer of the uterus returns to its original state. Inner layer of the uterus endometrium(mucous membrane) under the influence of ovarian hormones changes cyclically and is rejected at the end of the menstrual cycle, which leads to the exposure of small blood vessels and uterine (physiological) bleeding, called menstruation. Functions of the uterus: attachment to the mucous membrane of the zygote; growth and development of the placenta, embryo and fetus; membranes of the fetus, the formation of amniotic fluid; childbirth and placenta, menstrual.
Vagina(from Latin - vagina, from Greek - kolpos) is an extensible tube 7 to 13 cm long, 2.5 to 4.5 cm wide. Women who have given birth have a wider vagina than those who have not given birth. The vagina has three membranes: connective tissue, muscle and mucous. The mucous membrane of the vagina is covered with stratified squamous epithelium and has no glands. The vagina is hydrated by sweating fluid from the surrounding blood and lymph vessels. The walls of the vagina are easily compressed and stretched to accommodate the length and thickness of the penis, and stretch at birth and the placenta. The upper end of the vagina covers the cervix, and the lower end opens into the genital slit. There are four vaginal vaults around the cervix: anterior, posterior, left, and right. The posterior fornix of the vagina is deeper, sperm accumulates in it. In front of the vagina is the bladder, behind the rectum.
Functions of the vagina: protective, conductive and sexual. The protective function of the vagina is due to the fact that in the vagina of a healthy woman there are vaginal sticks (microbes) that secrete lactic acid. Therefore, the secret of the vagina has an acidic reaction. Lactic acid inhibits the growth of pathogenic microbes that have entered the vagina, which ensures its self-cleansing process. In principle, a healthy woman has fewer pathogenic microbes in her vagina than in her mouth. If the synthesis of female sex hormones is disturbed, the content of vaginal sticks decreases, the vaginal secretion becomes alkaline, which leads to the development of pathogenic microbes and inflammation of the vaginal mucosa. The acidic environment of the vagina ensures the movement of spermatozoa into the neutral or alkaline environment of the cervix. Through the vagina, the secret of the cervix and uterine cavity, the egg and menstrual blood are released into the external environment. The baby and placenta are born through the vagina and the amniotic fluid comes out. In sexually mature women, the vagina performs a sexual function.
Secondary female sex characteristics. These include the growth of pubic and axillary hair, a specific type of fat deposition under the skin, the growth of the pelvic bones in width, the growth of the mammary glands and the formation of menstrual function. Hair growth. subcutaneous fat layer. Pelvic bones. By the age of 14, short, stiff curly hair grows on the pubis of the girl, and straight hair in the armpits. Pubic hair grows in the form of a triangle, the base of which has a horizontal line (female type of hair growth). The deposition of adipose tissue under the skin, especially in the pelvic area, and the expansion of the pelvic bones in the horizontal direction give the girl's body a rounded shape and form a female body type. Milk glands(from lat. - mammae) are derivatives of the sweat glands, but functionally they are associated with the genitals. A person has one pair of mammary glands located on the chest, therefore they are also called mammary glands. By the time of birth in a girl and a boy, each mammary gland has a diameter of 0.4-2.5 cm. In men, the mammary glands remain in a rudimentary state for life. In girls, the mammary glands begin to develop at the age of 10-12 years under the influence of hormones from the hypothalamus, pituitary, ovaries, adrenals and thyroid. With the onset of menstruation, the growth of the mammary glands accelerates. The mammary glands reach their greatest development towards the end of pregnancy. With the end of lactation, the size of the mammary glands decreases. On the anterior surface of the gland is the nipple, the top of which has outlets for the milk passages. The nipple is surrounded by a pigmented area of skin called the nipple circle, or areola. The skin of the areola is bumpy, which is due to the sebaceous glands embedded in it and their openings. The skin of the areola and nipple contains nerve endings and smooth muscle fibers. With the contraction of muscle fibers, the nipple becomes dense, increases in length. This makes it easier for the baby to suck on the breast while feeding. The glandular tissue of the mammary gland consists of lobules, the excretory ducts of which are connected to the milk duct, which opens at the top of the nipple. Usually the nipple has 8-10 outlets of the milk passages. The mammary glands in shape and size have individual characteristics. They have developed erogenous zones.
Functions of the mammary glands of a woman: secretory, aesthetic and sexual. The secretory function of the mammary glands is manifested at the end of pregnancy and after childbirth and consists in the secretion of colostrum and milk. The process of formation and excretion of colostrum and milk is called lactation. Colostrum is a thick yellowish alkaline liquid. It is secreted in the last days of pregnancy and a few days after delivery. Colostrum is an indispensable food for a newborn baby in the first days of life. Compared to human milk, colostrum is high in protein, vitamins, antibodies, enzymes and minerals and low in fat and carbohydrates. Milk is a white alkaline liquid. Milk secretion begins 2-3 days after childbirth and may continue for the next 2-3 years after childbirth, while the woman is breastfeeding. After 1.5 years, the nutritional value of milk decreases. The secretion of milk and its separation are unconditioned and conditioned reflexes regulated by the central nervous system. The act of sucking causes irritation of the endings of the nerve fibers of the nipple and areola. Nerve impulses from them go to the cerebral cortex, and from there to the hypothalamus and pituitary gland, which produce hormones responsible for the secretion of milk (prolactin) and the exit of milk into the milk ducts (oxytocin). Negative emotions decrease and positive emotions increase milk secretion. Menstruation (from lat. menstruus - monthly) - periodic discharge of blood from the uterus through the vagina in a girl who has reached puberty, and in a woman of childbearing age. Menstruation is associated with the release of the female germ cell from the ovary into the abdominal cavity (ovulation). The menstrual cycle is the time from the first day of the previous menstruation to the first day of the next menstruation. Menstruation and the menstrual cycle are individual. In most women, the menstrual cycle is 26-30 days, less often - 21-24 days (shortened) or 30 or more days (long). In the middle of the cycle, the follicle that has matured in the ovary ruptures and the egg is released into the abdominal cavity. The probability of pregnancy in this phase is greatest. The duration of menstruation is 4-6 days, the amount of blood lost is about 50 ml. Less blood is released on the first and last days of menstruation. Sometimes on the first day of menstruation, bleeding is more pronounced. The duration of menstruation and the amount of blood loss can change under the influence of various factors (general and gynecological diseases, negative emotions, etc.). The first menstrual period in a girl is called menarche. Most girls in the first days of menstruation experience some kind of discomfort, which is due not only to the physiological processes occurring in the body, but also to the perception and evaluation of this new phenomenon. Girls, psychologically prepared for menstruation, perceive it as a normal phenomenon, indicating the entry into a new, promising adult life. As a rule, healthy women tolerate menstruation well. But on the first day of menstruation, especially in young girls, there may be a slight malaise, weakness, pain in the lower abdomen. Before menstruation, soreness of the mammary glands is possible. Some women during menstruation become more emotional, finicky, may be upset because of a trifle. But these are not symptoms of the disease. Therefore, you need to lead a normal way of life, work and rest. However, during menstruation, increased physical exertion should be avoided (lifting weights, jumping, cycling, horseback riding, etc.), you should not swim, take a bath, eat spicy food. You can take medications that reduce pain due to spasm of the muscles of the uterus (no-shpa, etc.). Every menstruating woman should know the duration of menstruation and the menstrual cycle and their characteristics. To do this, you need to mark the first and last days of menstruation in a pocket calendar. There may be a small discharge of blood from the vagina in the middle of the menstrual cycle associated with ovulation.
These include the labia majora, labia minora, and clitoris, which together make up the vulva. It is bordered by two folds of skin - the labia majora. They consist of adipose tissue, saturated with blood vessels, and are located in the anterior-posterior direction. The skin of the labia majora is covered with hair on the outside, and thin shiny skin on the inside, on which numerous gland ducts exit. The labia majora join in front and behind to form anterior and posterior commissures (commissures). Inward from them are the small labia, which are parallel to the large and form the vestibule of the vagina. Outside, they are covered with thin skin, and inside they are lined with a mucous membrane. They have a pink-red color, connect behind in front of the commissure of the large lips, and in front - at the level of the clitoris. They are quite richly supplied with sensitive nerve endings and are involved in achieving a voluptuous feeling.
On the eve of the vagina, the ducts of the Bartholin glands located in the thickness of the labia majora open. The secret of the Bartholin glands is intensively secreted at the time of sexual arousal and provides lubrication of the vagina to facilitate friction (periodic translational movements of the penis into the vagina) during intercourse.
In the thickness of the labia majora are the bulbs of the cavernous bodies of the clitoris, which increase during sexual arousal. At the same time, the clitoris itself also increases, which is a peculiar, greatly reduced likeness of the penis. It is located in front and above the entrance to the vagina, at the junction of the labia minora. There are a lot of nerve endings in the clitoris and during sex it is the dominant, and sometimes the only organ, thanks to which a woman experiences an orgasm.
Just below the clitoris is the opening of the urethra, and even lower is the entrance to the vagina. In women who have not lived sexually, it is covered by the hymen, which is a thin fold of mucous membrane. The hymen can have a variety of shapes: in the form of a ring, a crescent, a fringe, etc. As a rule, it breaks during the first sexual intercourse, which may be accompanied by moderate soreness and slight bleeding. In some women, the hymen is very dense and blocks the penis from entering the vagina. In such cases, sexual intercourse becomes impossible and you have to resort to the help of a gynecologist who dissects it. In other cases, the hymen is so elastic and pliable that it does not break during the first intercourse.
Sometimes with rough intercourse, especially in combination with a large penis, the rupture of the hymen can be accompanied by quite severe bleeding, such that the help of a gynecologist is sometimes necessary.
It is extremely rare for a hymen to have no opening at all. During puberty, when a girl begins her period, menstrual blood accumulates in the vagina. Gradually, the vagina overflows with blood and squeezes the urethra, making it impossible to urinate. In these cases, the help of a gynecologist is also needed.
The area located between the posterior commissure of the labia majora and the anus is called the perineum. The perineum consists of muscles, fascia, blood vessels, and nerves. During childbirth, the perineum plays a very important role: due to its extensibility, on the one hand, and elasticity, on the other, it passes the fetal head, providing an increase in the diameter of the vagina. However, at very large fruit or in a rapid delivery, the perineum cannot withstand overstretching and may rupture. Experienced midwives know how to prevent this situation. If all the techniques for protecting the perineum are ineffective, then they resort to a perineal incision (episiotomy or perineotomy), since an incised wound heals better and faster than a lacerated one.
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Internal female reproductive organs
These include the vagina, uterus, ovaries, fallopian tubes. All these organs are located in the small pelvis - a bone "shell" formed by the inner surfaces of the ilium, ischial, pubic bones and sacrum. This is necessary to protect both the woman's reproductive system and the fetus developing in the uterus.
The uterus is a muscular organ, consisting of smooth muscles, resembling a pear in shape. The size of the uterus is on average 7-8 cm long and about 5 cm wide. Despite its small size, during pregnancy, the uterus can increase 7 times. Inside the uterus is hollow. The thickness of the walls, as a rule, is about 3 cm. The body of the uterus - its widest part, is turned upward, and the narrower one - the neck - is directed downward and slightly forward (normal), falling into the vagina and dividing its posterior wall into the posterior and anterior vaults. In front of the uterus is the bladder, and behind is the rectum.
The cervix has an opening (cervical canal) that connects the vaginal cavity with the uterine cavity.
The fallopian tubes extending from the lateral surfaces of the bottom of the uterus on both sides are a paired organ 10-12 cm long. Departments of the fallopian tube: the uterine part, isthmus and ampulla of the fallopian tube. The end of the pipe is called a funnel, from the edges of which numerous processes of various shapes and lengths (fringes) extend. Outside, the tube is covered with a connective tissue membrane, under it is a muscular membrane; the inner layer is the mucous membrane, lined with ciliated epithelium.
The ovaries are a paired organ, the gonad. Oval body: length up to 2.5 cm, width 1.5 cm, thickness about 1 cm. One of its poles is connected to the uterus by its own ligament, the second is facing the side wall of the pelvis. The free edge is open into the abdominal cavity, the opposite edge is attached to the broad ligament of the uterus. It has medulla and cortical layers. In the brain - vessels and nerves are concentrated, in the cortex - follicles mature.
The vagina is an extensible muscular-fibrous tube about 10 cm long. The upper edge of the vagina covers the cervix, and the lower one opens on the eve of the vagina. The cervix protrudes into the vagina, a domed space is formed around the cervix - the anterior and posterior vaults. The wall of the vagina consists of three layers: the outer one is dense connective tissue, the middle one is thin muscle fibers, and the inner one is the mucous membrane. Some of the epithelial cells synthesize and store glycogen stores. Normally, the vagina is dominated by Doderlein sticks, which process the glycogen of dying cells, forming lactic acid. This leads to the maintenance of an acidic environment in the vagina (pH = 4), which has a detrimental effect on other (non-acidophilic) bacteria. Additional protection against infection is carried out by numerous neutrophils and leukocytes residing in the vaginal epithelium.
The mammary glands are composed of glandular tissue: each of them contains approximately 20 separate tubuloalveolar glands, each of which has its own outlet on the nipple. In front of the nipple, each duct has an extension (ampulla or sinus) that is surrounded by smooth muscle fibers. There are contractile cells in the walls of the ducts, which reflexively contract in response to sucking, expelling the milk contained in the ducts. The skin around the nipple is called the areola, it contains many mammary-type glands, as well as sebaceous glands, which produce an oily fluid that lubricates and protects the nipple during sucking.
The female reproductive system has a number of features:
1. The ability to fertilize a woman changes cyclically.
2. At a certain time, one or more eggs mature.
3. The process of egg formation is accompanied by cyclic changes in the level of hormones that cause structural and functional changes in the female reproductive organs.
4. The ovulatory, or menstrual, cycle is characterized by menstruation occurring at the end of each cycle, which is the rejection of the upper layer of the endometrium.
5. The menstrual cycle begins during puberty, is interrupted during pregnancy and lactation, and ends at menopause.
The complexity and multilevel regulation of the female reproductive system makes it subject to various influences.
Ovary - performs two functions: the formation of germ cells and the formation of sex hormones (estrogens). The menstrual cycle lasts about 28 days and is divided into three phases: follicular, ovulatory, luteal.
The follicular phase continues the first half of the cycle. Under the influence of FSH of the adenohypophysis, the development of primary follicles begins. There is a division of follicular cells that form estrogens. As the follicles mature, the amount of estrogen in the blood increases. In the middle of the cycle, the amount of estrogen reaches a maximum, which causes the release of LH into the blood. Under the influence of LH, the follicle ruptures and the egg is released - ovulation. In place of the follicle, a corpus luteum is formed, which forms the hormone progesterone.
Progesterone and LH act on the hypothalamic centers of thermoregulation, which leads to an increase in deep body temperature by 0.5 °C. The corpus luteum exists for approximately 14 days. Then, if fertilization does not occur, it dies, and the body temperature returns to its original level. At the time of ovulation, the egg is released from the ovary and enters the fallopian tubes. If fertilization does not occur, then after 14 days progesterone production falls and atrophy of the functional layer of the endometrium occurs - menstruation.
The role of estrogen
1. During puberty, affect the growth of the fallopian tubes, uterus, vagina, vulva, the formation of mammary glands and adipose tissue.
2. Division and growth of the functional layer of the endometrium of the uterus, the epithelium of the vagina.
3. Regulation of the release of LH and FSH due to the feedback mechanism (positive and negative).
4. Stimulate the synthesis of prolactin.
5. Cause retention of water and sodium salts in the body, affect the function of the sebaceous glands, skin. Reduce the level of cholesterol in the blood, thereby preventing the development of atherosclerosis in women of the reproductive period.
The role of androgens
The sources of androgens in a woman's body are the adrenal glands and ovaries. They affect the growth of hair in the armpit, pubis, distal limbs, sexual behavior.
The role of progesterone
Progesterone is the pregnancy hormone. The main targets are the uterus, mammary glands, brain. In the uterus, the hormone causes the growth of the endometrium, the development of its glands, the secretion of mucus, a decrease in tone, in the mammary glands - the development of alveoli and glandular epithelium. Affects the centers of thermoregulation and causes an increase in body temperature during ovulation.
Physiology of pregnancy and childbirth. Physiology of lactation.
It begins with the fusion of the egg and sperm. Fertilization takes place in the fallopian tube. Zygote cleavage begins immediately. On the 6-7th day, the embryo enters the uterine cavity and implantation occurs. The embryo secretes a hormone - chorionic gonadotropin (HR), which prevents the regression of the corpus luteum.
The corpus luteum of pregnancy is formed, which will perform an endocrine function until the formation of the placenta. During pregnancy, the placenta performs the following functions:
1) nutrition, gas exchange, removal of metabolic products;
2) barrier function;
3) endocrine (produces progesterone, GnRF, estrogens, protein hormones - placental lactogen, chorionic gonadotropin, prolactin).
Placental lactogen has the same effect as the growth hormone of the pituitary gland. It stimulates the growth of the fetus, the development of the mammary glands. Under the influence of a high level of estrogen in the pituitary gland of the mother, the secretion of PL begins, which prepares the mammary gland for lactation.
By the end of pregnancy, the level of estrogen in the mother's blood reaches a maximum. Estrogens increase the sensitivity of the uterus to oxytocin, which stimulates uterine contractions and induces labor. Ferguson reflex - mechanical irritation of the cervix and vagina causes activation of the hypothalamic nuclei of the SOYA and PVN, which release oxytocin into the blood.
Lactation is a complex physiological process of formation and excretion of milk. The physiology of lactation studies the pattern of growth and development of the mammary gland, interaction with other body systems, the formation of milk and its excretion. Feeding babies with milk provides the developing body of newborns in a wide variety of environmental conditions with good nutrition. The lactation period is the time during which the mammary gland synthesizes and secretes milk.
The shape of the uterus is pear-shaped, flattened in the anteroposterior direction. Wide uterine ligaments depart from the upper lateral edges of the uterus, in which the uterine (fallopian) tubes and ovaries are located (Fig. 1). Anatomically, the uterus is divided into fundus, body, and cervix.
The bottom is the part of the uterus located above the fallopian tubes. The body is triangular in shape, tapering towards the isthmus. The uterine cavity is also triangular in shape, in the upper corners there are two openings that open into the fallopian tubes, in the lower corner there is an isthmus - a narrowing leading to the cavity of the cervical canal (Fig. 2).
A stethoscope can also be used to avoid hearing. A urologist is something like a male gynecologist other than kidney and urinary tract surgery. There is no operation in medicine that would do this for suffering humanity like a prostatectomy. Every unnecessary word is useless.
The big ones love, the little ones just multiply. A woman loves a man, not who he is. Impotence is still the best contraceptive. Nature preserves the species, cares very little about the individual. The cause of many women's diseases is man.
Pregnancy is a specific infection transmitted by birds. For birth, make a smart look. Keep in mind that your face is usually the first thing a child sees. We age so fast that at night, when there is silence, we can hear the arteries working.
The cervix is the relatively narrow lower segment of the uterus. In girls and girls it has a conical shape, in an adult woman it is cylindrical. The vaginal part (portio vaginalis cervicis - ectocervix), the cervical canal (canalis cervicalis uteri - endocervix) and the isthmus are distinguished. There are two openings in the cervix: the internal os - an opening in the upper section, located on the border of the body and cervix, and the external os - an opening in the lower section that opens into the vagina.
The heart is like unheated plum dumplings. Cardiologist, he doesn't have a heart, he wants to replace patients with a pump. Modern trilogy: obesity - diabetes - hardening. Patients with intravenous nutrition always lie at the opposite end of the corridor.
Keep in mind that even bacteria are looking at us from the other side of the microscope. If we really knew how and what our body consists of, we do not dare to move. The spleen has a similar function as a public notary. I have always been despised by military affairs.
The job of a neurologist is to investigate whether a person will at some point be injured by a muscle in a completely different place, where no one but the neurologist would expect. Stomach ulcers are a contagious disease. Those who already have do so with others.
The vaginal part of the cervix is rounded, its surface is smooth, and the external os is located in the center. In nulliparous women, it is small, round or transversely oval (the mouth of a small fish). After childbirth, the external pharynx takes the form of a transverse slit. The cervical canal is narrow, expanded in the middle part. There are two longitudinal ridges on the anterior and posterior surfaces, from which mucosal folds extend at an angle, palm-shaped folds. These formations give the channel a bizarre appearance and are called the tree of life.
Cerebellum - cerebellum
The one who torments the eye is no longer interested in the future of the English fleet. By the way, do you believe in the middle ear? The physiologist will explain why the frog does not need a fetus, although most people do. Is masochism the inability to experience pleasure other than pain, or the ability to enjoy pain?
The brain is the apparatus by which we think what we think. Cosmetics deals with skin care until a skin care provider enters it. Definitions and goals, position in the system of biological sciences, the importance of teaching and research in pharmaceutical fields, the cell as the basic unit of the body, cell population - tissue-organ systems. Tissues: their development and differentiation in ontogenesis, the basics of typology - epithelium and glands, connective tissue and trophic tissue, muscle tissue, nervous tissue. Anatomical nomenclature, topographic relations on the body, movement system, general science of bones and muscles, their connection and mechanics, human skeleton, topography of muscle groups. Vascular system. Renal and urinary drainage, adrenal glands, male reproductive structure, structure of the female genital organs, fertilization and germline formation, mechanisms of differentiation and determination, critical and sensitive periods of development - significance for teratology, fetoplacental unit. The nervous system is the central nervous system. The structure and course of the spinal nerves, the construction and course of autonomic nerves, the structure and neural pathway of the visual apparatus, the structure and neural pathway of the auditory system, leather and infernal construction. Definition, content of physiology, homeostasis, composition of the human body, membrane transport, blood composition, its properties, blood groups, plasma, blood coagulation, lymph. Renal bleeding, glomerular and tubular functions of nephrons, activity of the urinary tract, composition and properties of urine, regulation of kidney function, functional tests on the kidneys. Physiology of the endocrine glands. Male and female reproductive system, hormonal regulation, pregnancy, blood circulation and fetal respiration, childbirth, lactation. Physiology of the digestive system. Physiology of the digestive tract, liver, pancreas, gallbladder, digestion and absorption of nutrients. Proteins, lipids, carbohydrates, vitamins, minerals in nutrition, rational nutrition. Physiology of the sense organs. Visual-auditory olfactory taste system, neuromuscular transmission, muscle contraction, muscle work, electrophysiology of muscle activity. Physiology of the central and peripheral nervous system. Reflex, receptor and nerve fibers, synapse, autonomic nervous system, activity of the spinal cord of the spine, spinal cord of the spinal cord, bridge, cerebellum, midbrain, midbrain, telencephalon.
- Cytology and general histology.
- Morphology of organ systems.
- Physiology of the circulatory system.
- Pulmonary ventilation, diffusion, perfusion, respiratory mechanism, respiratory control.
- Physiology of the excretory system.
The vagina is a muscular-elastic tube located in the small pelvis, the upper part covers the cervix, and the lower one opens into the genital gap.
The mucous membrane of the body of the uterus consists of a stroma and a single-layer cylindrical epithelium that grows into the stroma with the formation of simple tubular glands. The mucous membrane of the isthmus is similar to the mucous membrane of the body of the uterus and is represented by a large number connective tissue cells and single simple non-branching glands. The mucous membrane of the body and isthmus undergoes cyclical changes during the menstrual cycle.
Watch Movie: How Often Do We Have Sex?
The male reproductive system consists of internal organs, i.e. testicles, epididymis, seminal vesicles, follicular epithelial glands, ejaculatory duct, prostate and urethral tubular glands. External organs include the scrotum and penis.
Construction of the male genitalia
The nucleus is in the scrotum. It is covered externally by a serous membrane and internally by an epithelial membrane that passes into a septum separating the nuclei from the testicles. It is in these lobes that the nucleus is found in the nucleus. At first they are confused, but in the area of the nucleus niche they pass directly into the ducts and pass into the epididymal tubules.The wall of the cervix consists mainly of collagen tissue, the stroma of the mucous membrane contains many elastic fibers. The glands of the endocervix are tubular, branching, they are not considered true glands, since their structure is the same throughout. The glands contain a secret in the form of thick vitreous mucus, which has an alkaline reaction. The alkaline reaction contributes to the preservation of the viability of spermatozoa, their advancement into the uterine cavity. The secretion of mucus during ovulation increases, the secret fills the cervical canal and forms the so-called Christeller's plug, which, due to its bactericidal properties, mechanically prevents microbes from entering the canal and the uterine cavity. If the glands become blocked and mucus continues to accumulate, Nabothian cysts form, which can protrude onto the surface of the cervix.
Between the tubules are the cells responsible for the production of male sex hormones. In the nucleus is the spermatogenic epithelium, which consists of spermatids and spermatogonia - male reproductive cells - sperm. Nerves stick to the testicles along their back. Necrosis are tubules that form a cord of several meters that contains cilia that are responsible for sperm motility. Nourishes the sperm store until it reaches full maturity.
From there, the sperm goes to the pelvis, and outside the bladder enters the stomatal canal, where they connect with the seminal vesicle tube and form the ejection duct. It is located near the bottom of the bladder and is used to produce substances that provide energy for sperm.
The mucous membrane of the canal is represented by a cylindrical mucus-producing epithelium, there are single ciliated cells, their number decreases significantly with age.
The mucous membrane of the ectocervix and vagina is lined with stratified squamous non-keratinized epithelium. Normally, in the reproductive age, the epithelium consists of many rows, conditionally divided into three layers: basal, intermediate, superficial. Only the lower (basal) layer of cells is connected to the basement membrane, the cells in it are arranged in one row. A layer of young cells located above the basal layer, consisting of several rows (the lower part of the intermediate layer). It's called parabasal. Cell size increases with maturity. The size of the nuclei decreases (Fig. 3)
Ejaculatory tube and prostate gland
The injection tube is located inside the prostate. Its width narrows at the mouth of the urethra. The bulbous and tubular glands are responsible for the secretion of precum from the urethra, a secretion that protects sperm from the acidic environment of the urethra and vagina. This is a leather bag located in the vulva area. There are testicles in the scrotum.
The penis combines the function of the male reproductive system and the urinary tract. It is used both to remove urine from the bladder and to introduce semen into a woman's genitals, which is the solution of the penis. The skin covering the penis is thin and translucent, while the foreskin is the foreskin.
The structure of the stratified squamous epithelium of the vagina and the vaginal part of the cervix depends on the hormonal state of the woman, the phase of the menstrual cycle. There are 4 phases in the menstrual cycle: menstrual, folliculin (estrogenic, proliferative), ovulatory and luteal (progestin, secretory). These phases are associated with the maturation of the egg, which is regulated by gonadotropic hormones of the hypothalamic-pituitary system (anterior pituitary gland). Under the influence of FSH, the follicle grows and matures in the ovary (Fig. 4).
The sexual system must perform extremely important tasks. It is responsible not only for the production of female hormones, but also for the production of oocytes, for fetal development and hiatus. Due to his great responsibility, it is not surprising that the female sexual system sometimes begins to tremble.
Mice - structure, function and disease
Mice play an important role in the functioning of the female reproductive system. It's just inside her, it's an ovum an egg that her uterus protects and nourishes for the next 9 months. They also provide important non-reproductive functions, especially in bones, muscles, skin, the hematopoietic system, and the central nervous system. The site of androgen production is the gonads, both male and female, the adrenal glands, and the abdominal cortex. Androgens are steroids, derivatives.
The growing follicle secretes estrogen hormones, a certain amount of which inhibits the production of FSH and stimulates the release of LH. LH, together with FSH, prepares the follicle for ovulation, and after the rupture of the follicle (ovulation), if pregnancy has not occurred, it contributes to its transformation into a corpus luteum.
It is also wrong to associate a woman's health only with her reproductive function, which leads to the search for the causes of all pathologies only when the reproductive system changes. He is currently struggling with this belief. The slow development of the so-called. sex medicine.
Their action is not limited to the functioning of the reproductive system. From the first to the last months, they protect a woman's heart and blood vessels from meningococcal infection. Provides hydration to the skin and mucous membranes. Or a urologist. If you have the opportunity to be treated in a professional infertility clinic, you can use it. All consultants, as well as a professional laboratory.
The epithelium of the vagina is most susceptible to hormonal influences, therefore hormonal cytological diagnostics are based on the study of the composition of this epithelium (see Hormonal cytological diagnostics).
The cylindrical epithelium of the canal passes into a flat one in the so-called junction zone, located in a girl on the vaginal portion of the cervix, in a woman of reproductive age - at the level of the external os. The junction zone under the influence of hormonal and other influences can move to the vaginal portion of the cervix. The appearance of a cylindrical epithelium on the vaginal portion of the neck is called ectopia. Under the influence of the contents of the vagina, the ectopia site undergoes physiological changes, metaplasia into a squamous epithelium (Fig. 6).
 |
1 - mature epithelium. On the surface, mature cells of the surface layer with pyknotic nuclei 2 - the epithelium matures to the intermediate layer, mature intermediate cells on the surface 3 - the epithelium matures to the intermediate layer, immature intermediate cells on the surface The stand does not connect anything. It may not be a fungal infection and you will need to change your medications, such as antibiotics. Bleeding from the reproductive system is malignant. Once you've done any research, you can rule it out, though, if the bleeding occurs after each relationship and there is no tendency to stop. It is advisable to visit a gynecologist, conduct a laboratory test. Didn't find what you were looking for? The reproductive organs of the female are placed in the pelvis and include the ovaries, oviducts, uterus, and vagina. They are shown in the figure below. An anteroposterior view shows a diagram of the female reproductive system. Side view showing the position of the female reproductive organs in relation to the bladder and rectum. 4 - 5 - the epithelium matures only to the parabasal layer, parabasal cells on the surface |
Fig.5. Different stages of maturation of stratified squamous epithelium |
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A - before puberty (the junction zone is located in the cervical canal) B - C - during puberty (the junction zone is shifted to the vaginal part of the cervix) Diagram of the female reproductive tract. Cross section of the female reproductive tract illustrating the spatial and rectal connectivity of the bladder. Eggs are a smooth organ. They are located on either side of the uterus, next to the side wall of the pelvis. The eggs are responsible for oogenesis and cyclic ovulation in women after puberty. The ovaries exhibit endocrine effects consisting in the production of the hormones estrogen and progesterone, which control the maturation of follicles and prepare the uterus to receive a fertilized egg. A summary of the developmental stages of the egg and related hormones. Females are two wires about 10 cm long, through which the egg is transferred from the surface of the ovary to the uterine cavity. The funnel-shaped mouth of the fallopian tube surrounds the surface of the ovary and plays a role in the movement of the egg towards the fallopian tube. The ovum is transported along the fallopian tube through gentle peristaltic movements of the fallopian tube and a single-layer epithelial roll of tubular epithelium lining the fallopian tube. The mucous membrane of the fallopian tube is wrinkled, which provides the right conditions for the fertilization of the egg. D - the cylindrical epithelium on the vaginal part is replaced by metaplastic D - colposcopic picture of the cervix in a multiparous woman |
Fig.6. Location of columnar epithelium and junction area in the cervix |
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The formed corpus luteum under the influence of LH of the pituitary gland releases progesterone. There is a close relationship between the hormones of the ovary and adrenal gland, ovary and thyroid gland.
Estrogens stimulate the full maturation of stratified squamous non-keratinized epithelium to surface cells. Progesterone inhibits maturation, and if it is produced in large quantities, the cells mature only to the intermediate layer. In the postmenopausal period, due to a decrease in the production of sex hormones, the epithelium undergoes atrophy (Fig. 5).
The cylindrical epithelium on the vaginal part is replaced by metaplastic one. The area of metaplastic epithelium is called the transformation zone, or transformation zone. In women of reproductive age, the junction zone is usually represented by areas of the natural junction zone, areas of the transformation zone, and metaplastic epithelium. The transformation zone can be located on the vaginal part of the cervix, or it can (in whole or in part) go into the cervical canal. In postmenopausal women, the junction zone and the transformation zone are most often located in the cervical canal. The transformation zone is the most dangerous in terms of the possibility of pathological, including neoplastic changes.
Metaplastic squamous epithelium (Fig. 7) develops not from mature cylindrical, but from subcylindrical, so-called reserve cells. Normally, reserve cells are not usually found in histological and cytological preparations. Reserve cell hyperplasia is the first stage of squamous metaplasia. Under the layer of cylindrical cells, one, two or more layers of cells of the germinal type appear, which resemble the cells of the basal layer of the squamous epithelium without clear cell boundaries.
Mature metaplastic epithelium is morphologically almost indistinguishable from the "natural" squamous epithelium, represented by all layers typical of stratified squamous nonkeratinized epithelium.
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A - columnar epithelium B - a layer of subcylindrical (reserve) cells appears under the layer of cylindrical epithelium B - reserve cells multiply, cylindrical ones are sloughed off from the surface D - the stage of immature squamous metaplasia: clear boundaries of reserve cells are determined and 3-4 layers of cells are gradually formed, similar to stratified squamous non-keratinized epithelium D - stage of maturing squamous metaplasia. On the surface of the epithelial layer, medium-sized cells with small nuclei E - stage of mature squamous metaplasia. Cells on the surface of the epithelial layer are similar to intermediate cells of the squamous epithelium G - stage of mature squamous metaplasia. The cells on the surface of the epithelial layer are practically indistinguishable from the "natural" cells of the surface layer of the squamous epithelium. |
Fig.7. Stages of squamous metaplasia |
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Tatarchuk T.F., Solsky Ya.P., Regeda S.I., Bodryagova O.I.
Figure 1. Functional structure of the reproductive system
For a correct clinical assessment of neuroendocrine disorders in a woman’s body and, accordingly, for determining the principles and methods of their pathogenetic therapy, it is necessary, first of all, to know the five-link regulation of the reproductive system, the main function of which is the reproduction of a biological species (Fig. 1).
Chapter 1. Anatomy and physiology of the female reproductive system 9
The regulation of the function of the reproductive system is determined by the hypothalamic-pituitary link, which, in turn, is controlled by the cerebral cortex through neurotransmitters and neurotransmitters (Lakoski J.M., 1989).
The hypothalamus is a kind of biological clock of the body, that is, a system of self-regulation and automation of neuroregulatory processes that implements information coming from the external and internal environment of the body, thereby providing internal homeostasis necessary for the normal course of physiological processes. It is the hypothalamus that is the key link that coordinates the activity of the hypothalamic-pituitary-ovarian complex, the function of which is regulated by both CNS neuropeptides and ovarian steroids by the feedback mechanism (Wildt L., 1989; Sopelak V.M., 1997).
Given the fairly good illumination in contemporary literature of the peripheral link of the reproductive system, as well as the increasing role of ever-increasing psycho-emotional stress in the mechanisms of development of dishormonal disorders, we considered it appropriate to dwell in more detail on some aspects of the participation of suprahypothalamic structures in the regulation of the reproductive system.
As you know, the brain consists of two types of cells: neurons, which make up 10% of all brain cells, and glia - astrocytes and oligodendrites, which make up, respectively, the remaining 90%.
The development of neurons and glia occurs from a neuroepithelial precursor - a stem cell, which results in the synthesis of 2 cell lines: neuronal precursor cells, from which various types of neurons arise, and glial precursor cells, from which astrocytes and oligodendro subsequently develop. -quotes (Lakoski JM, 1989; Sopelak VM, 1997).
Neurons are highly differentiated cells with distinct sizes, shapes, and intracellular organelles. Like all other cells, with the exception of erythrocytes, neurons have a cell body, in the center of which there is a nucleus surrounded by a different volume of cytoplasm.
Receptive processes branch off from the surface of neurons - dendrites and the only main transmitting process - axon, which extends to its specific synaptic target cells and can vary significantly in length (Sopelak V.M., 1997).
The key life process of the neuron is concentrated in the cytoplasm of the cell body (also called the perikaryon), and then the products of neuronal synthesis are transported to the axons and dendrites. Bilateral transport between parts of the cell body and distal processes ensures the integrity of the neuronal function and is a constant energy-dependent well-coordinated process.
10 Endocrine gynecology
Glial cells (from the English word glue - glue) were originally considered as supporting brain cells, but research recent years determined their important functional role in the regulation of the vital activity of neurons. This class of non-neuronal cellular elements, 9 times the number of neurons, actually provides the interaction between them.
The most numerous glial cells are called astrocytes due to their multiprotrusion outlines. These cells are characterized by a unique expression of glial fibrillar acidic protein and are located between the outer surface of the vessels, neurons and their connections (Fig. 2). Astrocyte processes travel from neurons to capillaries, where they form a perivascular base.
Figure 2. The relationship of neurons, astrocytes and oligodendrocytes (Yen S.S.C., 1999)
The capillary base of astrocytes covers about 85% of the capillaries of the human brain and forms the blood-brain barrier.
Chapter 1. Anatomy and physiology of the female reproductive system 11
Another important class of glial cells are oligodendrocytes (cells with few short and thick processes) that form the myelin sheath of axons, which allows neurons to exert their effect quickly and without weakening over long distances within the nervous system. Oligodendrocytes also contain P450 steroid genesis enzymes and produce pregnanolone from cholesterol.
The determination of steroidogenesis enzymes in the brain tissue was one of the discoveries that contributed to the discovery of the mechanisms of CNS involvement in the regulation of reproductive function and, no less important, explaining changes in the CNS under the influence of changes in hormonal homeostasis.
The secretion of neuroactive steroids in astrocytes is higher than in oligodendrocytes and neurons, and therefore it is necessary to dwell on the characteristics of these cells in more detail.
The properties of astrocytes are different and not yet fully understood, although there is already evidence that astrocytes are paracrine cells for neurons:
In astrocytes, the presence of insulin-like growth factor (IGF) was revealed, the content of which increases towards the period of puberty, and also increases during estrogen treatment;
Pituicytes, as a type of astrocyte, are the main non-neuronal cellular elements in the neurohypophysis and play an important role in controlling the release of oxytocin and vasopressin from neurosecretory nerve endings;
The presence of luteinizing hormone (LH) and human chorionic gonadotropin (HCG) receptors in astrocytes suggests that LH and CG may affect the function of glial cells and, accordingly, the developmental processes and functioning of the brain;
Astrocytes are able to produce a variety of immunomodulatory molecules such as interleukins (IL-1, IL-2, IL-6), tumor necrosis factor a, transforming growth factor-os, interferon and prostaglandin E, while prolactin induces mitogenesis and cytokine expression in astrocytes;
Astrocytes, like neurons, are capable of producing corticotropin-releasing factor-binding protein (CRF-BP), which is widely distributed in the brain. Steroids such as dexamethasone, hydrocortisone, and to a lesser extent dehydroepiandrosterone inhibit the release of CRF-SP from astrocytes;
Astrocytes of hypothalamic origin secrete transforming growth factor a and (3), which stimulates the gene expression of gonadotropin-releasing hormones (Gn-RH) in neurons, while hypothalamic astrocytes are approximately 4 times more active than cortical astrocytes in relation to the synthesis of dehydroepiandrosterone ( DHEA).
Astrocytes may also be involved in the regulation of the neurotransmitter level of glutamate, which provides an excitatory effect, and γ-aminobutyric acid (GABA), which plays a key role in achieving an anxiolytic (calming) effect.
12 Endocrine gynecology
Currently, 3 main chemical forms of transmitters have been identified: amino acids, monoamines, and neuropeptides.
Amino acids act as transmitters both excitatory and depressing. In excitatory compounds of transmitter substances, acetylcholine, as well as glutamate and aspartate, are key. Inhibitory compounds are regulated by amino acids such as GABA and glycine.
Monoamines, as translators, consist of catecholaminergic (epinephrine, norepinephrine, and dopamine) and serotonergic transmitters. Thus, tyrosine comes from the bloodstream into catecholamine neurons and is the substrate from which tyrosine hydroxylase catalyzes the synthesis of dopa. Dopa is converted to dopamine by the amino acid decaroxylase (AKD). Dopamine-(3 oxidase (DVO) in noradrenergic neurons converts dopamine to norepinephrine (NA).
DA and NA are released into the synaptic cleft, where they rapidly bind to postsynaptic receptors. In plasma, excess transmitters undergo either metabolic inactivation by catechol-O-methyltransferase (COMT) or reuptake by presynaptic receptors where they undergo metabolic degradation by mono-amine oxidase (MAO) to form dehydroxyphenyl ethyl glycol (DOPEG).
Peptide transmitters. The peptide-containing neurons of the hypothalamus were originally described as neurosecretory neurons, but later it became known that almost all hypothalamic neuropeptides project to many areas of the brain. They provide neurotransmitter functions in the regulation of food intake, feeding and sexual behavior (Table 1).
Separately, we should dwell on the role of nitric oxide in the central and peripheral nervous system, the discovery of which radically changed the previously existing views on synaptic transmission. Although there is substantial evidence that nitric oxide functions as a neurotransmitter, it should be noted that this is an unusual transmitter, as it is a labile gas that cannot be stored in synaptic vesicles. Nitric oxide is synthesized from L-arginine with the help of oxidazot synthetase and enters from nerve endings by simple diffusion, and not by exocytosis like other neurotransmitters (Fig. 3). Moreover, nitric oxide does not undergo reversible reactions with receptors like all other reversible neurotransmitters, but forms covalent compounds with several potential targets, which include enzymes such as isonylate cyclase and other molecules.
: The action of reversible neurotransmitters is limited by presynaptic release or enzymatic degradation, while the action of nitric oxide is mediated by diffusion away from targets or by the formation of covalent bonds with the superoxide anion.
The formation of nitric oxide from arginine in the brain is catalyzed by oxidazot synthetase in the presence of oxygen with NADP as a coenzyme
Chapter 1. Anatomy and physiology of the female reproductive system 13
Table 1 Peptide transmitters in the CNS
(according to Yen S.S.C., 1999 with changes and additions)
and tetrahydrobioprotein as a cofactor. Regarding the role of nitric oxide in the central regulation of the reproductive system, it should be noted that NO is a neurotransmitter that regulates the release of GnRH.
Neurosteroids. The discovery of local estrogen synthesis in the hypothalamus (Naftollin et al, 1975) suggested that the brain has a function of steroidogenesis. In 1981, the presence of pregnanolone and pregnanolone sulfate, as well as dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEA-S) was found in the brains of adult male rats. This led to the discovery of mechanisms for the biosynthesis of steroids in the CNS, called neurosteroids.
In the human brain, neurosteroids, like neurotransmitters, are found in men and women over 60 years of age. DHEA, pregnanolone and progesterone are present in all parts of the brain, with their concentration in the brain several times higher than in plasma.
The presence of DHEA sulfate transferase and sulfatase was also found in the brain; therefore, it can be assumed that the synthesis of DHEA-S occurs directly in the brain.
14 Endocrine gynecology
Figure H. Formation of nitric oxide in the brain (Yen S.S.C., 1999)
Steroidogenic factor-1 (SF-1), a tissue-specific nuclear receptor, regulates the genes for several enzymes of steroidogenesis and is widely present in the human brain, including components of the limbic system.
Neurosteroids play an extremely important role in all life processes of the body, they modulate the activity of GABA receptors, glutamate receptors, affect cognitive function, have a trophic effect on the nervous tissue (promote myelination), modulate the production of releasing hormones in the hypothalamus (Yen SSC, 1999 ).
Figure 4. Sagittal section of the hypothalamic-pituitary junction (Solepak V.M., 1997)
The hypothalamus is a part of the diencephalon lying under the third ventricle between the optic chiasm and the median eminence, which connects to the posterior pituitary gland through the pituitary trunk, and also connects to the paired mastoid bodies (Fig. 4).
Chapter 1. Anatomy and physiology of the female reproductive system 15
The hypothalamus is interconnected with the CNS and pituitary gland through a variety of circulatory and neural connections. It consists of nerve cells grouped into nuclei. Cells grouped into the paraventricular and supraoptic nuclei of the hypothalamus continue to the posterior pituitary gland, where vasopressin, oxytocin, and neurophysins are released. At the same time, the supraoptic and paraventricular nuclei have a direct neural connection with the posterior pituitary gland. The supraoptic nuclei secrete mainly vasopressin, and the paraventricular nuclei secrete oxytocin, which is transported along the nerve endings to the posterior lobe (Sopelak V.M., 1997).
Other nuclei produce releasing and inhibitory factors (Gn-RH, TRH, somatostatin, corticotropin-releasing hormone (CRH), which are transported to the anterior pituitary through the circulatory portal system and control the secretion of the anterior pituitary.
Figure 5. Sagittal section of the pituitary gland (Solepak V.M., 1997)
Functional connections with the anterior pituitary gland are represented by the system of hypothalamic-pituitary blood vessels (Wildt L., 1989). Hypothalamic hormones enter the anterior lobe through the medial eminence and the hypothalamic-portal circulation. The hypothalamus also has intrahypothalamic neuronal connections, afferent fiber connections to the midbrain and limbic system, efferent fiber connections to the midbrain and limbic system, and the posterior pituitary gland. Hypothalamic factors are transported along the nerve fibers to the median eminence, where they penetrate the walls of the pituitary capillaries (Fig. 5). These factors influence the endocrine cells of the pituitary gland and provide specific hormonal responses (Yen S.S.C., 1999).
16 Endocrine gynecology
Speaking about the regulation of the reproductive system, it should be emphasized that under the influence of the releasing hormones of the hypothalamus, the synthesis of gonadotropic hormones in the pituitary gland is carried out. The place of synthesis of hypophysiotropic releasing hormones (liberins), which are decapeptides by chemical nature, is precisely the arcuate nuclei of the mediobasal hypothalamus. The production of releasing hormones occurs in a certain pulsating rhythm, called the circoral.
To ensure normal secretion of gonadotropins, it is sufficient to maintain a stable frequency of release of physiological amounts of GnRH. Changing the frequency of GnRH release changes not only the amount of LH and FSH secreted by the pituitary gland, but also their ratio, while even a tenfold increase in GnRH concentration leads only to a small increase in FSH release and does not change LH secretion in any way (Halvorson LM et al., 1999).
Thus, an increase in the rhythm leads to a significant increase in the release of FSH and to a decrease in the release of LH. In the luteal phase, progesterone, through endogenous opiates, slows down the frequency of the pulse generator, and this action is determined not by the concentration of progesterone, but by the duration of its effect. Estradiol, acting on the hypothalamus and gonadotropes (increase in the density of Gn-RH receptors), increases the amplitude of the LH / FSH wave.
The frequency of GnRH release in humans is 1 release in 70-90 minutes and corresponds to a number of biorhythms (alternation of sleep phases, fluctuations in the rate of glomerular filtration and gastric secretion, the frequency of hot flashes during menopause, etc.). Frequency modulation of information ensures the speed and reliability of the regulation of the reproductive system and its resistance to interference.
The pulse generator of the rhythm - the arcuate nucleus of the hypothalamus under physiological conditions receives information about the release of gonadotropins by the pituitary gland through a short feedback system, since special sphincters regulate pressure gradients in the portal blood flow system, and part of the blood from the pituitary gland returns to the hypothalamus, which provides a very high local concentration pituitary hormones in the hypothalamus (Yen S., 1999).
The synthesis and secretion of LH and FSH in the pituitary gland are carried out by the same cells (Halvorson L.M. et al., 1999). On the surface of gonadotrophs there are receptors for GnRH, the density of which depends on the level of steroid hormones in the blood and on the concentration of GnRH. The combination of GnRH with the receptor causes a massive influx of calcium ions into the cell, which, after a few minutes, leads to the release of LH and FSH into the bloodstream. In addition, GnRH stimulates the synthesis of LH and FSH and maintains the integrity of gonadotrophs (Wildt L., 1989).
An important role in the regulation of the function of the endocrine glands belongs to the pituitary gland. It lies in the Turkish saddle at the base of the brain, consists of the anterior (adenohypophysis), intermediate and posterior (neurohypophysis) lobes. The intermediate lobe is practically absent in humans. The pituitary gland connects to the hypothalamus through the pituitary trunk (see Fig. 5).
Chapter 1. Anatomy and physiology of the female reproductive system I?
The anterior pituitary gland is made up of five different types of cells that differ in immunological and ultrastructural characteristics. These cells in the anterior lobe produce 6 known hormones:
adrenocorticotropic hormone (ACTH), or corticotropin;
Thyroid-stimulating hormone (TSH), or thyrotropin;
Gonadotropic hormones: follicle-stimulating (FSH), or follitropin, and luteinizing (LH), or lutropin;
Somatotropic hormone (GH), or growth hormone;
Prolactin.
The first 4 hormones regulate the functions of the so-called peripheral endocrine glands, while growth hormone and prolactin act directly on target tissues (Halvorson L.M. et al., 1999).
Growth hormone and prolactin are produced by two types of cells - somatotrophs and lactotrophs (mammotrophs), belonging to the acidophilic series. ACTH and other fractions of proopiomelatocortin molecules, such as p-lipotropin and endorphins, are synthesized by thyrotrophs, while LH and FSH are synthesized by gonadotrophs belonging to the basophilic series.
Gonadotrophs make up 10-15% of the cellular composition of the anterior pituitary gland and are located near lactotrophs. This feature of localization suggests that there are paracrine relationships between the two types of these cells (Sopelak V.M., 1997).
As already mentioned, the secretion of these six anterior lobe hormones is controlled by hypothalamic releasing and inhibitory factors that are secreted from the hypothalamus and enter the pituitary gland via the hypothalamic-pituitary portal vessels. However, the production of tropic hormones can also be affected by other substances synthesized both in the central (P-endorphins) and in the peripheral (estradiol) parts of the reproductive system (Halvorson L.M. et al., 1999).
The neurohypophysis includes the pituitary trunk (see Fig. 5), the neural lobe, and the median eminence (special neural tissue at the base of the hypothalamus, which forms the main region for the transfer of pituitary-regulating neurosecretions to the anterior pituitary gland). Two posterior pituitary hormones (vasopressin and oxytocin) are stored in granules with their respective neurophysins, transported along the axons, and assembled in the axonal terminals, where they are stored until the appropriate impulses that trigger their release. Neuropeptides are released from secretory granules by exocytosis. This process includes the dissolution of the membranes of the neurosecretory granules and small area cell membrane at the end of the axon. The contents of the granules enter the intercellular space, and from there into the bloodstream (Sopelak V.M., 1997) .
The regulation of reproduction and the function of the gonads are carried out mainly by gonadotropic hormones secreted by the adenohypophysis, namely FSH, LH and prolactin. FSH - causes proliferation of granulosa
Endocrine Gynecology
Cells, stimulates the growth of follicles. LH - activates the synthesis of androgens and, together with FSH, promotes ovulation. The secretion of FSH and drugs is regulated by gonadotropin-releasing hormone by a feedback mechanism and also depends on the level of estrogens and androgens. Gonadoliberin (Luliberin) is secreted by pulses with a frequency of 1 pulse per hour to 1-2 pulses per day. Gonadoliberin secretion is controlled by sex and other hormones, numerous CNS neurotransmitters, including catecholamines, opiate hormones, etc. Gonadoliberin interacts with receptors located on the membranes of gonadotrophs, and the presence of the first three amino acids is required to activate the receptor. Gonadoliberin agonists (buzerilin, nafarelin, leuprolide, etc.) exert their effect through interaction with the same membrane receptors (Halvorson L.M., 1999).
Prolactin inhibits the production of gonadotropic hormones. Glucocorticoids also have an inhibitory effect on the release of LH.
According to the chemical structure, LH and FSH are glycoproteins consisting of two polypeptide subunits a and p. the a-subunit of these hormones is common for each glycoprotein and has the same amino acid sequence, the P-subunit differs among glycoproteins in the sequence of the amino acids included in it. It is the P-subunit that is responsible for hormonal specificity. Both subunits are individually biologically inactive. The formation of heterodimers is a prerequisite for the manifestation of biological activity (Halvorson L.M., 1999).
The half-life of gonadotropins circulating in the blood is directly related to the sialic acid component in the hormone molecule. Desialylation has been shown to shorten the half-life and biological activity of gonadotropins. FSH is in the blood in free form and its half-life is 55-60 minutes, and LH is 25-30 minutes. In reproductive age, the daily release of LH is 500-1100 mIU, in postmenopause the rate of LH formation increases and its amount is up to 3000-3500 mIU per day (Sopelak V.M., 1997).
Like steroids, gonadotropins have a biological effect on target tissues through the activation of specific receptors. However, unlike steroid hormones, gonadotropin receptors are associated with the membrane of target cells. Surface cell receptors for peptide glycoprotein hormones are proteins that are part of the structure of the cell membrane. After binding to gonadotropin, membrane receptors stimulate the production of soluble intracellular messengers, which, in turn, provide a cellular response (Halvorson L.M., ChinW.W., 1999).
The regulators of FSH production, according to modern concepts, in addition to hypothalamic liberins, are inhibin and activin, which are produced by ovarian granulosa and luteal cells, as well as cytotrophoblast cells (Hopko Ireland et al, 1994).
Chapter 1. Anatomy and physiology of the female reproductive system 19
Inhibin consists of two subunits of calamus. FSH affects the synthesis and release of inhibin by the feedback principle. The combination of the oc-subunit with the 3-subunit leads to suppression of FSH, and the combination of the two (3-subunits) leads to the formation of activin and, thus, to FSH stimulation.
The synthesis and release of FSH is also influenced by follistatin isolated from the follicular fluid. Follistatin is a glycoprotein that, like inhibin, reduces the release of FSH in a culture of gonadotropic pituitary cells. In addition, it has a high affinity for activin binding and less for inhibin binding. It has been established that follistatin and activin A are components of the autocrine-paracrine system of the follicle and are involved in the regulation of various functions of the cells of the inner membrane of the Graaffian vesicle (Grome N., O "Brien ML, 1996).
There are 3 types of gonadotropin secretion: tonic, cyclic and episodic, or pulsating (Halvorson L.M., Chin W.W., 1999).
Tonic, or basal, secretion of gonadotropins is regulated by negative feedback, and cyclic - by a positive feedback mechanism involving estrogens.
Pulsating secretion is due to the activity of the hypothalamus and the release of gonadoliberins.
The development of the follicle in the first half of the cycle is due to the tonic secretion of FSH and LH. An increase in the secretion of estradiol leads to inhibition of the formation of FSH. The development of the follicle depends on the number of FSH receptors in the cells of the granulosa zone, and the synthesis of these receptors, in turn, is stimulated by estrogens.
Thus, FSH leads to the synthesis of estrogens in a certain follicle, which, by increasing the number of receptors for FSH, contribute to its accumulation (by binding to its receptors), further maturation of the follicle and an increase in estradiol secretion. Other follicles undergo atresia at this time. The concentration of estradiol in the blood reaches a maximum in the preovulatory period, which leads to the release of a large amount of GnRH and a subsequent peak in the release of LH and FSH. A preovulatory increase in LH and FSH stimulates rupture of the Graafian vesicle and ovulation (Hurk Van Den R., 1994).
LH is the main regulator of steroid synthesis in the ovaries. LH receptors are localized on luteal cells, and the effect of LH is mediated through stimulation of adenylate cyclase and intracellular increase in cAMP levels, which directly or through intermediaries (protein kinase, etc.) activates enzymes involved in progesterone biosynthesis. Under the influence of LH in the ovaries, the amount of cholesterol necessary for the synthesis of hormones increases. At the same time, the activity of enzymes of the cytochrome P450 family, which cleaves off the side chain in the cholesterol molecule, increases. With a longer exposure, LH stimulates the expression and synthesis of other enzymes (3V-hydroxysteroid dehydrogenase,
20 Endocrine gynecology
17a-hydroxylase), involved in the synthesis of progesterone and other steroids. Thus, in the corpus luteum, under the influence of LH, the processes of steroidogenesis intensify at the site of cholesterol conversion to pregnanolone (Yen S., 1999).
The regulation of gonadotropin secretion is provided by "short" and "ultra-short" feedback circuits. Thus, an increase in the level of LH and FSH leads to inhibition of their synthesis and release, and an increased concentration of GnRH in the hypothalamus inhibits its synthesis and release into the pituitary portal system (Sopelak V.M., 1997).
The release of GnRH is also influenced by catecholamines: dopamine, adrenaline and norepinephrine. Epinephrine and norepinephrine stimulate the release of GnRH, while dopamine has the same effect only in animals that have been previously injected with steroid hormones. Cholecystokinin, gastrin, neurotensin, opioids and somatostatin inhibit the release of GnRH (Yen S., 1999).
Adrenocorticotropic hormone has a stimulating effect on the adrenal cortex. By increasing protein synthesis (cAMP-dependent activation), hyperplasia of the adrenal cortex occurs. ACTH enhances the synthesis of cholesterol and the rate of formation of pregnanolone from cholesterol. To a greater extent, its effect is expressed on the fascicular zone, which leads to an increase in the formation of glucocorticoids, to a lesser extent - on the glomerular and reticular zones, so it does not have a significant effect on the production of mineralocorticoids and sex hormones.
The extra-adrenal effects of ACTH are to stimulate lipolysis (mobilizes fats from fat depots and promotes fat oxidation), increased secretion of insulin and somatotropin, accumulation of glycogen in muscle cells, hypoglycemia, which is associated with increased secretion of insulin, increased pigmentation due to the action of melanophores on pigment cells .
Growth hormone is involved in the regulation of growth and physical development, having a stimulating effect on the formation of proteins in the body, RNA synthesis and transport of amino acids from the blood into cells.
The main biological role of prolactin is the growth of the mammary glands and the regulation of lactation. This is done by stimulating the synthesis of protein - lactalbumin, fats and carbohydrates of milk. Prolactin also regulates the formation of the corpus luteum and its production of progesterone, affects the water-salt metabolism of the body, retaining water and sodium in the body, enhances the effects of aldosterone and vasopressin, and increases the formation of fat from carbohydrates.
Posterior pituitary hormones are produced in the hypothalamus. In the neurohypophysis, they accumulate. In the cells of the supraoptic and paraventricular nuclei of the hypothalamus, oxytocin and antidiuretic hormone are synthesized. The synthesized hormones are transported by axonal transport with the help of the neurophysin carrier protein along the hypothalamic-pituitary tract to the posterior lobe of the pituitary gland. Here, hormones are deposited and subsequently released into the blood.
Chapter 1. Anatomy and physiology of the female reproductive system 21
Antidiuretic hormone (ADH), or vasopressin, has two main functions in the body. Its antidiuretic effect is to stimulate the reabsorption of water in the distal nephron. This action is carried out due to the interaction of the hormone with specific receptors, which leads to an increase in the permeability of the tubular wall, its reabsorption and concentration of urine. In this case, an increase in water reabsorption also occurs due to the activation of hyaluronidase in the cells of the tubules, which leads to increased depolymerization of hyaluronic acid, as a result of which the volume of circulating fluid increases.
In high doses (pharmacological), ADH constricts arterioles, resulting in an increase in blood pressure. Therefore, it is also called vasopressin. At its physiological concentrations in the blood, this action is not significant. An increase in the release of ADH, which occurs during blood loss, pain shock, causes vasoconstriction, which in these cases has an adaptive value.
An increase in ADH production occurs with a decrease in the volume of extracellular and intracellular fluid, a decrease in blood pressure, an increase in blood osmotic pressure, and activation of the renin-angiotensin and sympathetic nervous systems.
Oxytocin selectively acts on the smooth muscles of the uterus, causing it to contract during childbirth. This process is carried out by binding to special oxytocin receptors located on the surface membrane of cells. Under the influence of high concentrations of estrogens, the sensitivity of receptors to oxytocin sharply increases, which explains the increase in the contractile activity of the uterus before childbirth.
The participation of oxytocin in the process of lactation is to increase the contraction of the myoepithelial cells of the mammary glands, due to which the secretion of milk increases. An increase in the secretion of oxytocin, in turn, occurs under the influence of impulses from the receptors of the cervix, as well as mechanoreceptors of the nipples of the breast during breastfeeding.
The next level of the reproductive system is the ovaries, in which steroid and folliculogenesis occurs in response to the cyclic secretion of gonadotropins and under the influence of growth factors (FR).
The ovary is a paired organ of the female reproductive system and at the same time an endocrine gland. The ovary consists of two layers: the cortical substance, covered with a protein membrane, and the medulla. A section of the ovarian hilum is considered separately, devoid of theca-luteal cells of the stroma, containing granular cells, which are responsible for the production of ovarian androgens.
The cortical substance is formed by follicles of varying degrees of maturity (from primordial to atretic), located in the connective tissue stroma.
The process of folliculogenesis occurs continuously in the ovary and is regulated by gonadotropins by interacting with ovarian receptors (Sopelak V.M., 1997).
22 Endocrine gynecology
At the same time, several dozen follicles are detected in each ovary, which are in various stages of growth and maturation. The total number of follicles at birth is about 2 million. Their number is reduced by 8-10 times by the time the menstrual cycle is established, not exceeding 30-40 thousand. Only about 10% of follicles go through a full development cycle from premordial to ovulatory and turn into yellow body. The rest undergo atresia and reverse development (Hurk Van Den R. et al., 1994).
During the transformation of the primary follicle into a mature one, the first division of meiosis is completed, as a result of which the unidirectional (polar) body is released and an oocyte is formed. The transparent shell reaches its maximum development, turning into a radiant crown, covered with 1-2 layers of chaotically lying follicular cells. A cavity forms in the follicle, which reaches its maximum size before ovulation. The layer of follicular cells under the influence of stromal blood vessel growth factors turns into two layers: the inner and outer theca of the follicle. A further increase in the amount of follicular fluid leads to overflow of the follicle cavity and its rupture - ovulation. After ovulation, the oocyte, surrounded by a radiant crown, enters the funnel of the fallopian tube from the abdominal cavity and then into its lumen. Here, the second division of meiosis is completed and a mature egg is formed, ready for fertilization (Yen S., 1999).
The ovarian cycle consists of two phases - follicular and luteal, which are separated by ovulation and menstruation.
In the follicular phase, under the influence of FSH secreted by the pituitary gland, together with various growth factors, the growth and development of one or more primordial follicles are stimulated, as well as the differentiation and proliferation of granulosa cells. FSH also potentiates the activity of 17-(3-hydroxysteroid dehydrogenase and aromatase, which are necessary for the formation of estradiol in granulosa cells through cAMP activation, and thus stimulates the growth and development of primary follicles, the production of estrogens by follicular epithelial cells. Estradiol, in its turn, increases the sensitivity of granulosa cells to the action of FSH.FSH receptors belong to the group of membrane receptors with 7 transmembrane fragments.Along with estrogens, small amounts of progesterone are secreted.Of the many beginning growth of follicles, only 1 will reach final maturity, less often - 2-3 .
Preovulatory release of gonadotropins determines the process of ovulation. The volume of the follicle increases rapidly in parallel with the thinning of the follicle wall associated with increased activity of proteolytic enzymes and hyaluronidase secreted by polymorphonuclear leukocytes.
Observed within 2-3 days prior to ovulation, a significant increase in estrogen levels is due to the death of a large number of mature follicles with the release of follicular fluid. High concentrations of estrogen by the mechanism of negative feedback inhibit the secretion of FSH by the pituitary gland. Ovulatory LH surge and to a lesser extent
Chapter 1. Anatomy and physiology of the female reproductive system 23
The degree of FSH is associated with the existence of a positive feedback mechanism of ultra-high concentrations of estrogens and LH levels, as well as with a sharp drop in estradiol levels during the 24 hours preceding ovulation.
Neurohormonal regulation of the menstrual cycle is shown schematically in Figure 6.
I Ovulation
Figure 6. Neurohormonal regulation of the menstrual cycle
Ovulation of the egg occurs only in the presence of LH or human chorionic gonadotropin. Moreover, FSH and LH act as synergists during the development of the follicle, during which the theca cells actively secrete estrogens.
The mechanism of destruction of the collagen layer of the follicle wall is a hormone-dependent process, which is based on the adequacy of the follicular phase. The preovulatory surge of LH stimulates an increase in the concentration of progesterone at the time of ovulation. Due to the first peak of progesterone, the elasticity of the follicular wall increases, thus FSH, LH and progesterone jointly stimulate the activity of proteolytic enzymes: plasminogen activators secreted by granulosa cells promote the formation of plasmin, plasmin produces various collagenases, prostaglandins E and F2ot contribute to the displacement of the accumulation of cellular oocyte mass. In order to prevent premature luteinization of the non-ovulating follicle, a certain amount of activin must be produced in the ovary (Speroff L. et al., 1994).
After ovulation, there is a sharp decrease in the level of LH and FSH in the blood serum. From the 12th day of the second phase of the cycle, there is a 2-3-day increase in the level of FSH in the blood, which initiates the maturation of a new follicle, while the concentration of LH tends to decrease throughout the second phase of the cycle.
The cavity of the covulated follicle collapses, and its walls gather into folds. Due to rupture of blood vessels at the time of ovulation, hemorrhage occurs in the cavity of the postovulatory follicle. A connective tissue scar appears in the center of the future corpus luteum - stigma (Speroff L. et al., 1994).
24 Endocrine gynecology
The ovulatory release of LH and the subsequent maintenance of a high level of the hormone for 5-7 days activates the process of proliferation and glandular metamorphosis of the cells of the granular zone (granulosa) with the formation of luteal cells, i.e. the luteal phase (the corpus luteum phase) of the ovarian cycle begins (Erickson G.F., 2000).
Epithelial cells of the granular layer of the follicle multiply intensively and, accumulating lipochromes, turn into luteal cells; the shell itself is abundantly vascularized. The stage of vascularization is characterized by rapid multiplication of granulosa epithelial cells and intensive growth of capillaries between them. The vessels penetrate into the cavity of the postovulatory follicle from the side of thecae internae into the luteal tissue in the radial direction. Each cell of the corpus luteum is richly supplied with capillaries. The connective tissue and blood vessels, reaching the central cavity, fill it with blood, envelop the latter, limiting it from the layer of luteal cells. The corpus luteum has one of the highest levels of blood flow in the human body. The formation of this unique network of blood vessels ends within 3-4 days after ovulation and coincides with the heyday of the function of the corpus luteum (Bagavandoss P., 1991).
Angiogenesis consists of three phases: fragmentation of the existing basement membrane, migration of endothelial cells and their proliferation in response to a mitogenic stimulus. Angiogenic activity is under the control of major growth factors: fibroblast growth factor (FGF), epidermal growth factor (EGF), platelet growth factor (PGF), insulin-like growth factor-1 (IGF-1), as well as cytokines such as necrotic factor tumor (TNF) and interleukins (IL-1; IL-6) (Bagavandoss P., 1991).
From this point on, the corpus luteum begins to produce significant amounts of progesterone. Progesterone temporarily inactivates the positive feedback mechanism, and the secretion of gonadotropins is controlled only by the negative effect of zstradiol. This leads to a decrease in the level of gonadotropins in the middle of the corpus luteum phase to the minimum values (Erickson G.F., 2000).
Progesterone, synthesized by the cells of the corpus luteum, inhibits the growth and development of new follicles, and also participates in the preparation of the endometrium for the introduction of a fertilized egg, reduces the excitability of the myometrium, suppresses the effect of estrogens on the endometrium in the secretory phase of the cycle, stimulates the development of decidual tissue and the growth of alveoli in the mammary glands. The plateau of the serum concentration of progesterone corresponds to the plateau of the rectal (basal) temperature (37.2-37.5 ° C), which underlies one of the methods for diagnosing ovulation that has occurred and is a criterion for assessing the usefulness of the luteal phase. The increase in basal temperature is based on a decrease in peripheral blood flow under the influence of progesterone, which reduces heat loss. An increase in its content in the blood coincides with an increase in basal body temperature, which is an indicator of ovulation (McDonnel D.P., 2000).
Chapter 1. Anatomy and physiology of the female reproductive system 25
Progesterone, being an estrogen antagonist, limits their proliferative effect in the endometrium, myometrium and vaginal epithelium, causing stimulation of secretion containing glycogen by the endometrial glands, reducing the stroma of the submucosal layer, i.e. causes characteristic changes in the endometrium necessary for the implantation of a fertilized egg. Progesterone reduces the tone of the muscles of the uterus, causing them to relax. In addition, progesterone causes the proliferation and development of the mammary glands and during pregnancy contributes to the inhibition of the ovulation process (O "Malleu B.W., Strott G.A., 1999).
The duration of this phase of follicle development is different: if fertilization does not occur, then after 10-12 days the menstrual corpus luteum regresses, if the fertilized egg has invaded the endometrium and the resulting blastula begins to synthesize chorionic gonadotropin (CG), then the corpus luteum becomes the corpus luteum of pregnancy.
The granulosa cells of the corpus luteum secrete the polypeptide hormone relaxin, which plays an important role during childbirth, causing relaxation of the pelvic ligaments and relaxation of the cervix, and also increases glycogen synthesis and water retention in the myometrium, while reducing its contractility. During the normal menstrual cycle, its secretion rises immediately after the peak of LH release and remains detectable during menstruation. During pregnancy, circulating levels of relaxin are higher at the end of the first trimester compared to the second and third trimesters.
If fertilization of the egg does not occur, the corpus luteum enters the stage of reverse development, which is accompanied by menstruation. Luteal cells undergo dystrophic changes, decrease in size, while pycnosis of the nuclei is observed. The connective tissue, growing between the decaying luteal cells, replaces them, and the corpus luteum gradually turns into a hyaline formation - the white body (corpus albicans) (Sopelak V.M., 1997).
From the point of view of hormonal regulation, the period of regression of the corpus luteum is characterized by a pronounced decrease in the levels of progesterone, estradiol and inhibin A. A drop in the level of inhibin A eliminates its blocking effect on the pituitary gland and FSH secretion. At the same time, a progressive decrease in the concentration of estradiol and progesterone contributes to a rapid increase in the frequency of GnRH secretion, and the pituitary gland is released from negative feedback inhibition. A decrease in the levels of inhibin A and estradiol, as well as an increase in the frequency of Gn-RH secretion impulses, ensure the predominance of FSH secretion over LH. In response to an increase in FSH levels, a pool of antral follicles is finally formed, from which a dominant follicle will be selected in the future. Prostaglandin F2a, oxytocin, cytokines, prolactin and 02 radicals have a luteolytic effect, which may be the basis for the development of corpus luteum insufficiency in the presence of inflammatory process in appendages.
The duration of the ovarian (menstrual) cycle normally varies from 21 to 35 days.
Menstruation occurs against the background of regression of the corpus luteum. By the end of it, the levels of estrogen and progesterone reach their minimum. Against this background, there
26 Endocrine gynecology
Activation of the tonic center of the hypothalamus and pituitary gland and increased secretion of predominantly FSH, which activates the growth of follicles. An increase in the level of estradiol leads to stimulation of proliferative processes in the basal layer of the endometrium, which ensures adequate regeneration of the endometrium (Fig. 7).
Figure 7. Links of regulation of the normal menstrual cycle (Sopelak V., 1997)
Chapter 1. Anatomy and physiology of the female reproductive system 27
Ovarian steroidogenesis takes place in the epithelial cells lining the cavity of the follicle, in the cells of the internal theca, and much less in the stroma. Follicular epitheliocytes, stromal and theca tissue synthesize progesterone, testosterone, dehydrotestosterone, estrone and estradiol (Erickson G.F., 2000).
Estrogens are estradiol, estrone and estriol. Biologically the most active is estradiol, 95% of which is formed in the follicle, and its level in the blood is an indicator of the maturation of the follicle. Estradiol (E2) is secreted predominantly by granulosa cells and, to a lesser extent, by the corpus luteum. Estrone (E,) is formed by peripheral aromatization of estradiol. The main source of estriol (E3) is the hydroxylation of estradiol and estrone in the liver (O "Malleu B.W., Strott G.A., 1999).
Estrogens secreted into the blood are conjugated by sexsteroid-binding globulin (SHBG) and, to a lesser extent, by blood albumin. SHBG is also known as estradiol-testosterone-binding globulin. The name itself indicates the increased affinity of this protein for androgens. The level of sex hormone-binding globulin in the blood serum of women is almost 2 times higher compared to its concentration in the blood of men. Estrogens and their metabolites are conjugated in the liver with glucuronic and sulfuric acids and excreted in bile and urine (McDonnel D.P., 2000).
In addition to the already mentioned effect on the genital organs, the pituitary gland and the hypothalamus, estrogens have anabolic properties, increase bone tissue metabolism and accelerate the maturation of the bones of the skeleton, which is the reason for the cessation of growth at the onset of puberty, on the one hand, and the development of juvenile osteoporosis in girls with delayed sexual development - on the other.
In large doses, estrogens contribute to the retention of sodium and water in the body until the development of edema. They also affect lipid metabolism, lowering blood cholesterol levels.
Progesterone is secreted by the corpus luteum, as well as by the adrenal cortex and testicles, where it is used as a precursor for the biosynthesis of corticosteroids and androgens. Progestogens and glucocorticoids have a similar chemical structure, so progesterone and glucocorticoid receptors have cross-linking properties. In serum, progesterone is bound by transcortin, which is also known to bind glucocorticoids. According to some studies, the ability of progesterone to bind transcortin even exceeds that of corticosteroids. In the liver, progesterone binds to glucuronic acid and is excreted in the urine in a conjugated state (McDonnel D.P., 2000). However, the effect of estrogens and progesterone on target organs is described in more detail in the section "Principles of the use of sex steroid hormones in clinical practice and their systemic effects".
Androgens in women are secreted by the cells of the ovarian stroma, mainly in the form of androstenedione, and in the adrenal glands it is formed 3 times more than in the ovaries. Androstenedione is converted to testosterone in peripheral tissues. In the ovaries, it is formed in small
28 Endocrine gynecology
Quantities also testosterone, dihydrotestosterone, dehydroepiandrosterone. Approximately 1/4 of the testosterone that is secreted in a woman's body is produced in the ovaries. The rest of its amount is secreted by the adrenal glands or formed in tissues in the periphery by conversion from androstenedione (McDonnel D.P., 2000).
The biological effect of steroids in target tissues is associated with the presence of specific receptors in them (Fig. 8). Steroids diffuse through the cell membrane and bind to specific receptors in the cytoplasm. Steroid receptors are relatively large proteins with a high binding capacity to certain hormones. However, binding of these receptors to other steroids of this group (for example, synthetic agonists and antagonists) is possible. Cytoplasmic receptors are not present in all, but only in tissue cells that are sensitive to this species hormone. The steroid-receptor complex, the formation of which depends on several factors, including temperature, moves to the nucleus, where there are special sites on the chromatin that bind these complexes. The steroid-receptor complex becomes activated, after which it can bind to an acceptor nuclear protein located on DNA. The latter interaction leads to the synthesis of a large number of specific RNA and corresponding proteins, the growth and development of the corresponding organs (mammary glands, uterus, etc.) and tissues (O "Malleu B.W., Strott G.A., 1999).
Figure 8. The mechanism of action of steroid hormones on target tissues (Cowan B.D., 1997)
The number of receptor molecules for various steroid hormones ranges from 5,000 to 20,000 per cell. Estrogen receptors bind many
Chapter 1. Anatomy and physiology of the female reproductive system 29
Gee natural and synthetic estrogenic steroids with the same affinity. It is believed that the estrogen and progesterone receptors are two subunits, each of which binds a hormone molecule, as described in more detail in the clinical chapter "Principles of the use of sex steroid hormones in clinical practice."
Each of the a and P subunits interacts with chromatin and provides further activation of specific genes and RNA polymerases.
The biological effect of the hormone is associated not only with its quantitative fluctuations in the blood serum, but also with the state of the receptor link, and the number of receptors is subject to significant fluctuations. Experimental studies have shown that target tissues in newborn rats contain a small amount of estrogen receptors. On the 10th day of life, the number of receptors increases, and after this period, the introduction of exogenous estrogens causes their increase. Estrogens stimulate the formation of receptors not only for estrogen, but also for progesterone. The number of receptors not only depends on the level of the hormone circulating in the blood, but is also under genetic control. Thus, the complete absence of androgen receptors is observed in testicular feminization syndrome (McDonnel D.P., 1999).
Figure 9. Chemical structure of steroid hormones (Sopelak V., 1997)
An analysis of the chemical structure of the main sex steroid hormones shows that they are all derivatives of progesterone, and estrogens differ from each other only in the number of hydroxy radicals present in their structure (Fig. 9).
30 Endocrine gynecology
The substance for all steroid hormones is low-density lipoprotein cholesterol (LDL). Gonadotropins (FSH and LH), as well as enzyme systems (aromatases) are involved in steroidogenesis. First, pregnanolone is formed as a result of the cleavage of the side chain of cholesterol. In the future, two ways of metabolic transformations of pregnanolone are possible, ending with the formation of testosterone, which received the names of the m- and n5-metabolism pathways based on the position of the double unsaturated bond in the resulting compounds. The predominant formation of sex steroids occurs along the L5 pathway. In its course, 17a-hydroxypregnanolone, dehydroepiandrosterone (DHEA), androstenedione are sequentially formed. Progesterone, 17a-hydroxyprogesterone, androstenedione are formed along the L4 pathway. A4,5-isomerase closes both pathways. Next, the aromatization of testosterone or androstenedione occurs with the formation, respectively, of estradiol or estrone (Fig. 10).
Note: GSD - 3p-hydroxysteroid dehydrogenase, DOC - deoxycorticosterone
Figure 10. Biosynthesis of steroids (Cowan B.D., 1997)
Most steroidogenic enzymes that convert cholesterol into precursors and into biologically active steroids belong to the P450 cytochrome group. Cytochrome P450 is a generic term for many oxidative enzymes (Bryan D., 1997). There are about 200 types of cytochromes, of which five are involved in the process of steroidogenesis (Table 2).
P450 enzymes involved in the process Table 2
Steroidogenesis
Chapter 1. Anatomy and physiology of the female reproductive system 31
The peripheral link of the reproductive system is represented by target organs, which include the genitals and mammary glands, as well as the skin and its appendages, bones, blood vessels, adipose tissue. The cells of these tissues and organs contain receptors for sex hormones, which are cytoplasmic receptors - cytosol receptors. Also, receptors for sex hormones are found in all structures of the reproductive system and, most importantly, in the central nervous system (McDonnel D.P., 2000).
Thus, the reproductive system is a single integral system, all links of which are interconnected both by a direct and feedback mechanism.
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