Sexual behavior in women. Hormonal regulation of the female reproductive cycle Age-related changes in the organs of the female reproductive system
The secretion of female sex steroid hormones (estrogens and progesterone), as well as ovogenesis and ovulation, occur in the ovaries cyclically - within the framework of the ovarian cycle with an average duration of 28 days. Fluctuations from 21 to 32 days are possible. Menstrual the cycle ensures the integration in time of various processes necessary for reproductive function: egg maturation and ovulation, periodic preparation of the endometrium for implantation of a fertilized egg, changes in the woman's body, including behavior.
Ovarian the cycle consists of three phases: follicular (from the 1st to the 14th day of the cycle), ovulatory (13th day of the cycle) and luteal (from the 15th to the 28th day of the cycle). After the completion of the previous cycle, the new follicle is included in the new cycle. The growth of the follicle occurs under the influence of the pituitary follicle-stimulating hormone (FSH) - the follicular phase. At this time, the formation of the outer and inner membranes of the follicle occurs, the egg grows and matures. Envelope cells increase as they grow estrogen synthesis, the concentration of estrogen depends not only on FSH, but also on LH and increases towards the middle of the cycle.
It is estrogens that determine the changes that occur in a woman's body in the first half of the cycle. Consider their effects in relation to various organs. First of all, estrogens enhance the growth and development of the egg and the follicle itself. In the uterus, under the influence of hormones, the proliferative phase begins, during which the endometrial mucosa thickens and its glands develop. In the hypothalamus in the first quarter of the cycle, under the influence of small concentrations of hormones, the secretion of FSH and LH increases, at the peak of estrogen concentration - the middle of the cycle - the secretion of FSH is suppressed.
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Effects of estrogen
| in the ovaries | · Growth and development of the ovaries themselves · Formation of follicles · Increased sensitivity of follicles to gonadotropins (FSH and LH) and prolactin · Increase in the number of estrogen receptors. |
| In the uterus | Growth of the endometrium and myometrium. Early effects - 15 min - 8 hours: increase in RNA polymerase activity, release of prostaglandins, watering, increase in the concentration of growth factors, accumulation of eosinophils from the blood. Late effects 6 - 28 hours: increase in the amount of RNA polymerase, protein synthesis, proliferation of myometrial and endometrial cells · Increased contractility of the myometrium. · Increased sensitivity to progesterone associated with increased synthesis of receptors. Increase in the number of receptors for oxytocin and NA. |
| In the mammary glands | Growth of mammary ducts |
| In the brain | · Estrogens are the main inducers of sexual differentiation of the hypothalamus and pituitary gland. The preovulatory rise in estrogen levels enhances the secretion of gonadoliberins, increases the sensitivity of gonadotropes to their action. The influence of estrogens on the ventromedial nuclei causes the corresponding sexual behavior. |
| In other organs | In the liver, the synthesis of hormone carrier proteins increases. In the kidneys, an increase in ARP (plasma renin activity), therefore, sodium and water retention. The anabolic effect, however, is much weaker than the effects of androgens Increased fat deposition |
The follicular phase of the cycle ends with ovulation, which occurs at the peak of LH secretion, note that without luteinizing hormone, ovulation does not occur, in which case the cycle becomes anovulatory. After ovulation, the corpus luteum of the ovary, which develops at the site of the burst follicle, begins to produce a hormone - progesterone. Progesterone secretion is regulated by LH. The main function of progesterone is to prepare the endometrium for implantation of a fertilized egg and ensure the normal course of pregnancy. If fertilization does not occur, the corpus luteum degenerates.
Progesterone together with estrogen regulates morphological changes in the uterus and mammary glands, enhancing the processes of proliferation and secretory activity. As a result, in the secretion of the endometrial glands, the concentrations of lipids and glycogen, which are necessary for the development of the embryo, increase. Progesterone enhances hyperplasia and hypertrophy of the myometrium during pregnancy and reduces the excitability of the uterus. In non-pregnant women, progesterone is involved in the regulation of the menstrual cycle. The hormone promotes the growth of alveoli in the mammary glands. In the hypothalamus, high concentrations of progesterone suppress the secretion of all tropic hormones: FSH, LH, PRl. That is why bleeding occurs - the rejection of a new mucous layer with blood vessels. In the brain, under the influence of progesterone, a decrease in excitability is observed. Progesterone enhances basal metabolism and increases basal body temperature, which is used in practice to determine the time of ovulation.
The regulation of the menstrual cycle is carried out by gonadoliberin and gonadotropins.
GONADOLIBERIN - a hypothalamic decapeptide that regulates the secretion of both follicle-stimulating (FSH) and luteinizing (LH) hormones. The ability of GL in some cases to stimulate the synthesis and release of FSH, and in others LH is explained by the modulating effect of sex hormones (different levels during the sexual cycle) and the participation of prostaglandins.
GONADOTROPINS - adenohypophysis hormones - follicle-stimulating (FSH) and luteinizing (LH).
Even from a fugitive review of cyclical changes various parts of the female genital apparatus, it is clearly seen that all periodic phenomena must be coordinated with each other to a certain extent. Each organ plays its own role in reproduction. It is not enough that he periodically fulfill this role with maximum efficiency; the period of readiness of each organ or part of it should come when the entire complex mechanism of reproduction is ready for functioning.
For a long time with certainty established that hormones control and coordinate in time the various stages of the sexual cycle. The interaction of these hormones is very complex. It took a long and persistent experimental work to refine the results obtained under the influence of any one hormone. A much more difficult task is to interpret the effects of several hormones acting together or sequentially.
Currently in biology there is no area where research is as intense as in endocrinology. Almost every biological or medical journal adds to our knowledge about the methods of formation, chemical properties, or physiological action of hormones. Nevertheless, it is not yet possible to give at least a brief approximate sketch of some of the most important hormones that regulate the sexual cycle, without the proviso that most of the data has been obtained recently, has not yet been thoroughly verified, and therefore a clear idea of \u200b\u200bthe subject will develop only in the future.
Paradoxically, the primary sexual process activator- the pituitary gland is not located near the reproductive organs, but is located deep in the skull, in close connection with the brain. The pituitary gland, slightly larger than a cherry pit, is an inconspicuous mass of tissue, but its action has long aroused the curiosity of man. In the Middle Ages, scientists argued about whether the pituitary gland is the permanent seat of the soul or a special organ that secretes mucus from the brain.
It is currently established that pituitary at different times it produces from 5 to 15 hormones, most of which are known by several names.
Long before the onset of sexual maturity the anterior lobe of the pituitary gland, through one of the hormones it produces, begins to influence the development of the genital organs. In young hypophysectomized animals, the reproductive organs remain underdeveloped, the characteristic sexual cycle is not established, and the individual turns out to be sterile. Although it has long been known that early spaying does not cause a menstrual cycle at all and that spaying at puberty results in the cessation of menstruation, we are only now beginning to understand that the causes of these changes run much deeper. Even before the ovary begins to activate the uterus, it must first come into a state of functional activity under the influence of the stimulating effects exerted on it during its growth by the hormone of the anterior pituitary gland.
We recommend watching the tutorial video:This action pituitary gland is only the beginning of a whole series of processes. After reaching puberty, the pituitary gland begins to produce hormones that have a profound effect on the gonads and are therefore called gonadotropic hormones, in contrast to other hormones of pituitary origin that act on other organs, such as thyroid-stimulating and adrenocorticotropic hormones. Currently, it is believed that there are two gonadotropic hormones, one of which stimulates the development of the follicle, and the second - the development of the corpus luteum.
Hormone, stimulating follicle development, activates their consistent growth and maturation. Here another link in the chain of hormonal action occurs: when the follicles enlarge, they begin to produce a hormone that can be obtained from the follicular fluid. This hormone is estradiol. Injection of the required amount of estradiol in experimental animals that did not have estrous changes due to total oophorectomy led to the restoration of typical symptoms of estrus.
On this basis estradiol often referred to as the estrogen hormone. The value of estradiol, the amount of which increases significantly at the time of ovulation, is quite obvious. The maximum amount of this hormone, which stimulates sexual activity, is observed in the period preceding the release of the egg from the follicle into the abdominal cavity.
Following ovulation, another group is activated hormones. A hormone from the anterior pituitary gland, which stimulates the development of the corpus luteum, causes rapid proliferation of the epithelial cells of the ruptured follicle. At the same time, the chemical properties of these cells change, which is associated with the formation of the corpus luteum. In turn, the corpus luteum, under the influence of additional stimulation from the lactogenic hormone, produces a hormone that acts on the uterus. This hormone, called progesterone, induces changes in the lining of the uterus to prepare it for pregnancy.
Here again, obviously speaks a clear consistency in time, because the chain of processes that leads to the preparation of the uterus for the perception of the embryo begins even during the first stages of the development of the egg.
With such sequences phenomena, the relationship between ovulation and menstruation is of particular importance. If ovulation takes place, say, on the 13th day of the menstrual cycle, and sexual intercourse occurs at about the same time, this allows the embryo to develop within 7 days, which contributes to its successful implantation in the already prepared uterine mucosa. During these 7 days, under the influence of the corpus luteum hormone, the mucous membrane of the uterus thickens, its glands become active, the amount of blood in it increases. When the uterus is in this premenstrual phase, it is already ideally prepared to receive and strengthen the embryo.
It turned out that corpus luteum hormone in addition to its effect on the uterus, it has another equally important physiological effect. Injection of corpus luteum extract has been repeatedly shown to delay ovulation. This action is determined by the relationship in time between the maximum development of the corpus luteum of ovulation and other phenomena of the cycle. The corpus luteum reaches a noticeable degree of development and acquires histological signs of active secretion a few days after the rupture of the follicle from which it was formed.
On microscopic examination it can be seen that regressive changes in the corpus luteum appear when the next menstrual period should begin, and the corpus luteum reaches a noticeable decrease in size by the time the new follicle matures. These data showed that the corpus luteum of ovulation is a source of a hormone that acts as an antagonist of pituitary follicle-stimulating hormone, causing a delay in the development of subsequent follicles.
The phenomena of the sexual cycle were presented in the simplest form, without excessive detailing of a number of facts that make these phenomena one of the most fascinating areas of modern biological science. However, even this brief sketch shows how marvelously coordinated the whole mechanism of reproduction is. So far, we have only seen a series of changes that are repeated in preparation for pregnancy. Ovulation is a critical event, to which all other cyclic changes are timed. The ovum released during the rupture of the follicle is ready for fertilization and all other organs are also ready to play their role if the ovum is fertilized.
The sexual cycle is also called the menstrual cycle. These are changes occurring periodically in the body of a woman of reproductive age, which are aimed at the probable possibility of conception. In medicine, the first day of menstruation is considered to be the beginning of the menstrual cycle. In total, it includes three phases, which we will discuss in this article. These are proliferative, menstrual and secretory. If in animals females are capable of sexual behavior at any time, then in humans, after about five hundred cycles, menopause occurs. This occurs between the ages of 46 and 54. In this condition, the ovaries become insensitive to luteotropin and follitropin.
Duration
The duration of the sexual cycle in women can be different. The physiological processes taking place in her body are of decisive importance. At the same time, there are approximate deadlines in which it should fit. If this does not happen, then there is reason to suspect various violations.
The duration of the sexual cycle in a woman is 28 days. Depending on various factors, it can vary, becoming a week longer or shorter.
First menstruation
To understand the concept of the sexual cycle, one should delve into the specialized terminology related to this condition. This article will discuss the main terms.
The central event in the process of sexual development of every woman is the menarche. This is the first sexual cycle in her life. It indicates that the body is now ready for reproduction. As a rule, in women, menarche occurs at the age of twelve to fourteen years. The norm is considered to be between the ages of nine and fifteen.
With the appearance of menstruation at the age of nine, they speak of early menarche, and at 15 years of age - of primary amenorrhea. The time at which the first menstrual bleeding occurs depends on many factors. This is nutrition, heredity, the general health of the girl.
Possible violations
Violations of the sexual cycle can be caused by a large number of different factors. These are pregnancy, hormonal disruptions in adolescence, and other natural causes. The menstrual cycle can also go astray due to internal and external stresses.
It is customary to talk about a delay in menstruation if there are no cyclic bleeding within 35 days. It should be noted that small delays in menstruation are considered normal. However, only if their duration does not exceed ten days.
One of the most common reasons for missed periods is pregnancy. In this case, a test should be purchased to confirm. If the result is negative, you should consult a gynecologist. He will understand the causes and, if necessary, prescribe the appropriate treatment.
The causes of violations of the regulation of the sexual cycle can be a large number:
- neurological and mental diseases;
- mental shocks;
- obesity;
- avitaminosis;
- infectious diseases;
- liver problems;
- diseases of the hematopoietic system, blood vessels or heart;
- consequences of gynecological operations;
- violation of puberty;
- urinary tract injury;
- genetic diseases;
- hormonal changes that occur during menopause.
It is worth noting that in adolescents, a delay in menstruation is a common occurrence. In the first couple of years after the onset of menstruation, girls rarely experience a constant cycle. In this case, do not worry, this is a common occurrence. It is due to the fact that at this age the hormonal background is still unstable, therefore, ups and downs in mood are likely, which leads to a significant increase or decrease in the level of hormones in the blood. When the hormones stop raging, the cycle immediately stabilizes. If it does not become regular two years after the onset of menstruation, you should consult a gynecologist for help.
Climax
Termination of regular periods of the sexual cycle occurs during menopause. This is characterized by the extinction of the reproductive function. Irregular periods or their complete cessation is called menopause.
When this time comes, mainly depends on heredity. Medical interventions, in particular, gynecological operations, and certain diseases, can also have an impact. All these problems can lead to early menopause.
Phases
The processes that occur during menstruation make up the phases of the sexual cycle, they are also called stages.
They correspond to the changes that occur in the ovaries and endometrium, that is, the internal mucous membrane of the uterus that lines its cavity.
Follicular phase
The first stage of the sexual cycle is called the menstrual or follicular. At this stage, the woman begins to bleed from the uterus. This happens due to the rejection of the endometrial layer, which is abundantly supplied with blood vessels.
Rejection begins at the end of the ovarian cycle. It occurs necessarily only if the egg has not been fertilized. The beginning of the first stage of the sexual cycle or the follicular phase of the ovary is considered the very first day of menstruation. The duration of this period may be different, for each woman it is individual. During this time, the dominant follicle should finally mature. On average, it is two weeks, but the time interval from seven to 22 days is considered the norm.
The course of the menstrual cycle
The follicular phase and the accompanying ovarian cycle begin with the release of GnRH by the hypothalamus. It actively stimulates the pituitary gland to secrete small amounts of luteinizing and follicle-stimulating hormones. These are, respectively, lutropin and follitropin.
Due to the reduced level of estradiol secretion, the release of lutropin and follitropin is suppressed. As a result, their level of education remains low.
Under the influence of follitropin, several follicles begin to develop in the ovaries at once. Of these, the dominant follicle stands out, which has the maximum number of receptors for folliculotropin. In addition, it most intensively synthesizes estradiol. The rest at the same time undergo atresia, that is, the reverse development of follicles in the ovary.
Over time, the level of estradiol in the body begins to rise. At its low concentration, the secretion of gonadotropins is suppressed, and at a high one, on the contrary, it is stimulated. As a result, these processes lead to a significant release of GnRH by the hypothalamus.
This effect is especially pronounced for lutropin, since a high concentration of estradiol increases the sensitivity of adenohypophysis cells. In addition, the follicles react much more intensively to lutropin due to the presence of a larger number of receptors for this hormone.
The result of this is regulation according to the principle of positive feedback. The follicle continues to increase in size exactly until a sharp release of lutropin begins. This means the end of the follicular phase.
ovulatory phase
The new phase is called ovulatory or proliferative. Around the end of the first week of the cycle, the dominant follicle is released. It continues to grow steadily, and also increases the amount of estradiol. At this time, the remaining follicles undergo reverse development.
The follicle, which finally matures and is ready for ovulation, is scientifically called the Graafian vesicle. It is worth noting that the ovulatory phase lasts only about three days. During this time, the main release of luteinizing hormone occurs.
Hormone release
Within one and a half to two days, several waves of release of this hormone happen in a row at once, its concentration in the plasma at this time increases significantly. The release of luteinizing hormone is the final stage of follicle development. In addition, it stimulates the production of proteolytic enzymes and prostaglandins, which are required to break the wall of the follicle and release the egg. This is the process of ovulation itself.
In parallel, the level of estradiol in the body begins to fall. A feature of the sexual cycle is that in some cases it may be accompanied by ovulatory syndrome. It is characterized by painful and uncomfortable sensations in the abdomen, iliac regions.
As a rule, ovulation occurs within a day after the maximum wave of luteinizing hormone release. A period of 16 hours to two days is considered the norm. This is an important part of the sexual reproduction cycle.
During ovulation, a woman's body releases from 5 to 10 ml of follicular fluid, which contains the egg necessary for conception.
secretory phase
This phase of menstruation is also called the luteal phase. This is the period of time between ovulation and the onset of the next menstrual bleeding. It is also known as the corpus luteum phase. Unlike the previous follicular phase, the duration of this stage is considered to be more constant. It is from 13 to 14 days, normally it can be more or less by two days.
When the graafian vesicle ruptures, its walls immediately subside, and the luteal pigment and lipids penetrate into the cells. Due to this, it acquires a characteristic yellow color. After transformation, the follicle is already called the corpus luteum.
In total, the duration of the luteal phase depends on the period of functioning of the corpus luteum. As a rule, it is ten to twelve days. At this time, it secretes estradiol, progesterone and androgens. In the presence of elevated levels of progesterone and estrogen, the outer layers of the endometrium change. Her glands mature, begin to secrete and proliferate. This is a clear sign that the uterus is preparing to receive a fertilized egg.
Estrogen and progesterone reach their peak around the middle of the luteal phase, while the amount of the corresponding hormones decreases in parallel.
If pregnancy does not occur...
When the egg remains unfertilized, the corpus luteum stops functioning after a while. The level of progesterone and estrogen decreases. Because of this, swelling and necrotic changes in the endometrium occur.
By reducing the level of progesterone, the synthesis of prostaglandins also increases. When the egg is not fertilized, after some time luteolysis begins in the corpus luteum, that is, structural destruction, since it is no longer able to synthesize estradiol and progesterone.
Because of this process, the secretion of lutropin and follitropin is no longer suppressed by anything. The secretion of these hormones increases, which leads to the stimulation of a new follicle. With a decrease in the level of progesterone and estrogen, the synthesis of follicle-stimulating and luteinizing hormones resumes. Thus begins a new cycle in the body of a woman.
Stages of arousal
An important place in the reproductive system is occupied by the stages of excitation of the sexual cycle. There are three of them in total. These are excitation, inhibition and balancing. During this period, changes occur, some of which are easy to notice, while others are elusive even for modern biological devices.
At the stage of sexual arousal in the female body, follicles mature and ovulation occurs. During this period, he is ready to conceive.
During inhibition, signs of sexual arousal appear much weaker. Then comes the stage of balancing, which continues again until a new stage of excitation. During this period, the woman is in the most balanced state. This is influenced by the processes that occur in the body.
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Completed by: student of the 238th group of the pharmaceutical faculty Kaldashova Larisa Petrovna Checked by: candidate of biological sciences, associate professor Gerasimova O.V. SAMARA 2015slide 2
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MENSTRUAL CYCLE Cyclic changes in the organs of the female reproductive system, the main manifestation of which are monthly bloody discharge from the genital tract - menstruation. CLINICAL CHARACTERISTICS OF THE MENSTRUAL CYCLE Menstruation begins during puberty at 11-15 years of age and continues until the onset of menopause at the age of 45-55 years. In women, the average cycle is 28 days. Allocations last from 3 to 7 days. Blood loss averages 50-80 ml.
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PHASES OF THE MENSTRUAL CYCLE The menstrual cycle of women consists of four phases, which are characterized by certain changes occurring in the body. It should be borne in mind that the duration of each phase of the menstrual cycle in each case is as individual as the cycle itself.
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MENSTRUAL PHASE The first phase of the menstrual cycle begins on the first day of menstruation. During menstrual bleeding under the influence of hormones, the endometrium of the uterus is rejected, and the body prepares for the appearance of a new egg. In the first phase of the cycle, algomenorrhea is often observed - menstruation. Algomenorrhea is a disease that must be treated by eliminating the causes in the first place.
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FOLLICULAR PHASE The second phase of the menstrual cycle lasts about two weeks after the end of menstruation. The brain sends impulses, under the influence of which the follicle-stimulating hormone, FSH, enters the ovaries, which promotes the development of follicles. Gradually, a dominant follicle is formed, in which the egg subsequently matures. The second phase of the menstrual cycle is also characterized by the release of the hormone estrogen, which renews the lining of the uterus. Estrogen also affects the cervical mucus, making it immune to sperm. Some factors, such as stress or illness, can affect the length of the second phase of the menstrual cycle, and delay the onset of the third phase.
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OVULATION PHASE The phase lasts about 3 days, during which there is a release of luteinizing hormone (LH) and a decrease in follicle-stimulating hormone (FSH). LH affects the cervical mucus, making it receptive to sperm. Also, under the influence of LH, the maturation of the egg ends and its ovulation occurs (release from the follicle). A mature egg moves into the fallopian tubes, where it waits for fertilization for about 2 days. The most suitable time for conception is before ovulation, since spermatozoa live for about 5 days.
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LUTEAL PHASE After the egg is released, the follicle (corpus luteum) begins to produce the hormone progesterone, which prepares the endometrium of the uterus for the implantation of a fertilized egg. At the same time, the production of LH stops, the cervical mucus dries up. The luteal phase of the menstrual cycle lasts no more than 16 days. The body is waiting for the implantation of the egg, which occurs 6-12 days after fertilization.
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The phases of the menstrual cycle are due to the influence of hormones that affect not only physiological processes, but also the emotional state. And although the modern rhythm of life requires women to be constantly active, observing changes in the emotional state associated with the phases of the menstrual cycle will help determine the most unfavorable days for action or conflict resolution. This approach will allow you to avoid unnecessary stress and maintain your strength and health.
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FERTILIZATION is the process of fusion of a spermatozoon with an egg, leading to the formation of a new single-celled organism - a zygote. About once a month, a fertile woman ovulates. This is the process of release of an egg ready for fertilization from the follicle. In most cases, one sperm and one egg are involved in fertilization.
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FERTILIZATION However, for the fertilization process to take place, the sperm must first reach the egg. Once in the vagina, the seminal fluid of a man contains from 100 to 400 million spermatozoa. The speed of their movement is only 2-3 mm per minute. After 1-2 minutes, they reach the uterus, thanks to its contractions and contractions of the tubes. 2-3 hours after sexual intercourse, the spermatozoa reach the end sections of the fallopian tubes, in which they merge with the egg. Then the fertilized egg moves along the fallopian tube, thanks to its peristaltic movements and the movements of the ciliated epithelium. Approximately 7-8 days after fertilization, the egg enters the uterine cavity. There it is introduced into the mucous membrane, which contains nutrients for the development of the embryo. From the moment of fertilization, pregnancy begins.
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DEVELOPMENT OF THE HUMAN FEMO The embryonic (embryonic) development of a person is an early period of development up to 8 weeks. During this time, a body is born from a fertilized egg, which has all the main features of a person. After eight weeks of development, the intrauterine organism is called the fetus, and the development period is fetal.
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SPERMATOZOID IN THE UTERINE TUBE EGG MEETING OF THE SPERMATOZOID WITH THE EGG. OVIDUCT
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Two sperm make contact with the egg, but only one should remain. Sperm inside the egg
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Day 8: The fertilized egg travels down the oviduct to the uterus and the embryo attaches to the wall of the uterus. Embryonic brain development begins
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On the 40th day, the embryonic cells form the placenta. The placenta forms a protective barrier, provides oxygen to the fetus through the mother's circulatory system, and carbon dioxide is transported in the opposite direction. Through the placenta, the fetus receives water, electrolytes, nutrients and minerals, vitamins; the placenta is also involved in the removal of metabolites (urea, creatine, creatinine).
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Week 8: The ears and face are formed, the rudiments of the gill slits atrophy. The embryo is surrounded by an aqueous membrane. Fingers and hands are well defined and outlined, toes are clearly defined, muscle movements begin. The fetus begins to react with feelings. The embryo reacts to irritation with a thin hair on the skin of the cheeks by moving the head, moving the trunk and pelvis back, stretching out the arms and hands to remove the hair (perhaps the first manifestation of tactile sensitivity). The sensation then spreads to the rest of the body.
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Week 10: All major body parts are in place. The eyes and ears are in a normal position. The skeleton is clearly defined. The child's airway, which starts at the nose and continues to the lungs, is ready for the first breaths. The eyes are half closed. The eyelids will close over the next few days.
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Week 16: Formed limbs with fingers and nails. Taste buds are surrounded by pores and cells with microvilli that complete the taste perception system and begin to function. After this, there are no significant changes in these receptors, except that their number increases, and they also develop in breadth and depth. The first manifestations of facial expressions: the ability to squint the eyes, to smile mockingly. Thumb sucking begins. The development of olfactory receptors is completed. The embryo is able to distinguish several hundred odors.
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Week 18: Feel the movement of the fetus, hear the heartbeat. At this time, the fetus begins to hear. The length of the embryo is 140-190mm. Week 20: The skin of the fetus is covered with the finest (vellus) hairs (especially in the eyebrows and eyelashes. Week 24: Development of facial expressions: pouting lips, frown, muscle tension around the eyes, associated with the crying of the child.
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6 months: About 8-10 weeks before birth. The fetus at this time turns over to come out head first. Week 36: The fetus is fully formed, the skin is covered with primordial lubrication, the length of the hair on the head reaches 25 mm. A hormonal signal is sent to the mother's body, requiring the end of pregnancy.
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Hormonal changes and the role of placental hormones in the body In the relationship between the organisms of the mother and fetus, the placenta plays the role of an endocrine gland. The processes of synthesis, secretion and transformation of a number of hormones of protein and steroid structure take place in it. There is a close relationship between the body of the mother, fetus and placenta in the production of hormones. Some of them are secreted by the placenta itself and transported into the blood of the mother and (or) the fetus. Others are derivatives of precursors that enter the placenta from the body of the mother and fetus.
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The placenta is a powerful endocrine gland, in which the processes of synthesis, secretion and transformation of a number of hormones, both steroidal (gestagens and estrogens) and proteinaceous (CG, PL), proceed intensively. Hormones specific to pregnancy. - HG. - PL. - Hormones of the hypothalamus. - Corticoliberin. pituitary hormones. - Prolactin. - Somatotropic hormone. - ACTH. - Other peptide hormones. - Insulin-like growth factor I and II. - Parathyroid-like peptide. - Renin. - Angiotensin II. - Steroid hormones (estrogen, progesterone). - 1,25-dihydroxycholecalciferol.
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The main hormone of the fetoplacental system is estriol, which is called the protector of pregnancy. It makes up 85% of all estrogen during pregnancy. Its main role is the regulation of uteroplacental circulation, i.e. supplying the fetus with all the vital substances necessary for normal growth and development. Estriol is synthesized in the placenta from dehydroepiandrosterone sulfate, which is formed in the fetal adrenal cortex and, to a lesser extent, in the pregnant adrenal cortex. 90% of estriol in the blood of a pregnant woman is of fetal origin and only 10% is maternal. Part of the estriol is in the free state in the blood of the pregnant woman and the fetus, performing its protective function, part enters the liver of the pregnant woman, where, by combining with glucuronic acid, it is inactivated. Inactivated estriol is excreted from the body of a pregnant woman with urine.
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In a much smaller amount than estriol, other estrogens are formed in the fetoplacental system - estrone and estradiol. They have a diverse effect on the body of a pregnant woman: they regulate water-electrolyte metabolism, cause sodium retention, an increase in circulating blood volume (BCC), vasodilation and an increase in the formation of plasma steroid-binding proteins. Estrogens cause the growth of the pregnant uterus, cervix, vagina, promote the growth of the mammary glands, change the sensitivity of the uterus to progesterone, which plays an important role in the development of labor. The content of hormones in the blood at different stages of pregnancy
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The second important steroid hormone of pregnancy is progesterone. Progesterone causes changes in the mother's body that contribute to the onset and development of pregnancy. Under its influence, secretory processes occur that are necessary for the implantation and development of the fetal egg. Progesterone also promotes the growth of the genital organs of a pregnant woman, the growth and preparation of the mammary glands for lactation, is the main hormone that reduces the contractility of the myometrium, reduces the tone of the intestines and ureters, has an inhibitory effect on the central nervous system, causing drowsiness, fatigue, impaired concentration, and in addition, it contributes to an increase in the amount of adipose tissue due to the hypertrophy of fat cells. The metabolite of progesterone, pregnandiol, is excreted in the urine.
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The main protein hormones of pregnancy are human chorionic gonadotropin (CG) and placental lactogen (PL). - HCG is a glycoprotein produced by the chorion even before the formation of the placenta. In terms of its biological properties, it is similar to LH of the pituitary gland, contributes to the preservation of the function of the corpus luteum of the ovary, affects the development of the adrenal glands and fetal gonads, and affects the processes of steroid metabolism in the placenta. CG is found in the urine already on the 9th day after fertilization, reaches a peak concentration by 10-11 weeks of pregnancy (about 100,000 units) - PL is a polypeptide hormone, in its chemical and immunological properties it approaches the growth hormone of the anterior pituitary gland and prolactin . PL can be detected in the blood from the 5th week of pregnancy. PL affects the metabolic processes that are aimed at ensuring the growth and development of the fetus. PL gives an anabolic effect, retains nitrogen, potassium, phosphorus, calcium in the body; has a diabetic effect. PL, due to its anti-insulin action, leads to an increase in gluconeogenesis in the liver, a decrease in the body's tolerance to glucose, and an increase in lipolysis.
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The physiological action of hormones is aimed at: - providing humoral, i.e. carried out through the blood, the regulation of biological processes; - maintaining the integrity and constancy of the internal environment, harmonious interaction between the cellular components of the body; - regulation of growth, maturation and reproduction processes. Hormones regulate the activity of all body cells. They affect mental acuity and physical mobility, physique and height, determine hair growth, voice tone, sexual desire and behavior.
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In women with the onset of puberty, ovulation is periodically repeated. The sexual cycle lasts 27-28 days. It is divided into four periods: 1) pre-ovulation, 2) ovulation, 3) post-ovulation (metaoestrus), 4) rest period. Each of these periods is characterized by certain changes in the body (Fig. 110).
preovulation period. During this period, preparation for pregnancy takes place. In many animal species with seasonal mating, the pre-ovulation period is also the period of preparation of the female reproductive apparatus for sexual intercourse. They are in heat during this period and the female allows the male to have sexual intercourse.
In the preovulatory period in women, the uterus increases in size and becomes full-blooded; the mucous membrane of the uterus and its glands grow; peristaltic contractions of the uterine (fallopian) tubes and the muscular layer of the uterus increase and become more frequent; the vaginal mucosa grows, the number of deflated epithelial cells increases in the vaginal mucus. The reason for all these changes is the increased secretion of follicle-stimulating hormone from the pituitary gland.
Follicle-stimulating hormone also acts on immature female animals. If such females are injected daily with this hormone, then they will have changes characteristic of the pre-ovulation period in the uterus and vagina, and ovulation may occur. If in sexually mature female animals at the beginning of the preovulation period the pituitary gland is surgically removed, the development of preovulatory changes in the uterus and vagina stops and ovulation does not occur.
All preovulatory changes are caused by pituitary gonadotropic hormones due to their effect on the intrasecretory function of the ovaries. In the ovaries at this time, there is an increased production of estrogens, which stimulate the growth of the uterus and its mucous membrane, the proliferation of the mucous epithelium of the vagina and increase the contraction of the uterus and fallopian tubes. If women who, for medical reasons, have had their ovaries removed and, as a result, there is no sexual cycle, are given increasing amounts of estrogens for several days, then they will experience typical preovulatory changes in the uterus and vagina.
Rice. 110. Changes in the ovary and uterine lining during a normal menstrual cycle
(a-b) and during the menstrual cycle, which ended in pregnancy (b-d) (scheme).
1 - the level of estrogen in the blood; 2 - the level of progesterone in the blood; 3 - follicle and corpus luteum cycle a - b;
4 - follicle and corpus luteum of cycle b-d; 5-changes in the mucous membrane of the uterus. Numbers below-
cycle days.
In a normal body, a gradually increasing amount of follicle-stimulating hormone accelerates the final maturation of the most mature of the vesicular "ovarian follicles (Graaffian vesicles). The surface of this vesicle breaks and an egg comes out of it - in other words, ovulation occurs.
Ovulation period. This period begins from the moment of rupture of the vesicular ovarian follicle, the release of the egg from it and the movement through the fallopian tube into the uterus. During the passage through the fallopian tube, fertilization of the egg can occur. A fertilized egg, getting into the uterus, is attached to its mucous membrane. The sexual cycle is interrupted and pregnancy occurs. After the release of the egg, a corpus luteum begins to develop in place of the bursting ovarian follicle, the cells of which produce the hormone progesterone. At the same time, the production of estrogen in the ovaries continues: it is secreted by numerous maturing follicles.
The ovum released from the ruptured vesicular ovarian follicle is sent to the fallopian tube by the movements of the ciliated epithelium. The contraction of the smooth muscles of the tubes at this time is enhanced under the influence of an increased amount of estrogen in the blood. Due to this, the egg is initially pushed through the tube rather quickly. As the developing corpus luteum secretes more and more progesterone in the ovary, peristaltic contractions of the tubes become less frequent and weaker, as progesterone counteracts the stimulatory effect of estrogen on the contractions of the muscles of the tubes and uterus. In general, it takes about 3 days for the egg to pass through the tube to the uterus. If fertilization of the egg does not occur, then the post-ovulation period begins.
post-ovulation period. Women during this period have menstruation. Animals (with the exception of monkeys) do not menstruate. An unfertilized egg, having entered the uterus, remains alive in it for several days, and then dies. Meanwhile, under the influence of progesterone, the release of gonadotropic hormones from the anterior pituitary gland decreases. The decrease in the follicle-stimulating hormone of the pituitary gland leads to a decrease in the formation of estrogens in the ovaries, therefore, the factor that caused and maintained the preovulatory changes in the tubes, uterus and vagina drops out. The decrease in the luteinizing hormone of the pituitary gland causes atrophy of the corpus luteum with its replacement by a connective tissue scar, as a result of which the ovarian production of progesterone stops. Preovulatory changes in the uterus, tubes and vagina begin to decrease.
