Sufi whirling for women. Whirling chakras

Respiratory function.

Gas exchange in the placenta is carried out by the penetration of oxygen to the fetus and removal of CO2 from its body. These processes are carried out according to the laws of simple diffusion. The placenta does not have the ability to accumulate oxygen and CO2, therefore, their transport occurs continuously. Gas exchange in the placenta is similar to gas exchange in the lungs. Amniotic fluid and paraplacental metabolism play a significant role in removing CO2 from the fetus.

Trophic function.

The fetus is nourished by transporting metabolic products across the placenta.

Proteins. The state of protein metabolism in the mother-fetus system is determined by many factors: the protein composition of the mother's blood, the state of the protein-synthesizing system of the placenta, the activity of enzymes, the level of hormones and a number of other factors. The placenta has the ability to deaminate and transaminate amino acids, synthesize them from other precursors. This causes the active transport of amino acids into the blood of the fetus. The content of amino acids in the blood of the fetus slightly exceeds their concentration in the blood of the mother. This indicates an active role of the placenta in protein metabolism between the mother and the fetus. The fetus synthesizes its own proteins from amino acids, which are immunologically different from those of the mother.

Lipids. The transport of lipids (phospholipids, neutral fats, etc.) to the fetus is carried out after their preliminary enzymatic breakdown in the placenta. Lipids enter the fetus in the form of triglycerides and fatty acids. Lipids mainly localized in the cytoplasm of the syncytium of the chorionic villi, thereby ensuring the permeability of the cell membranes of the placenta.

Glucose. It crosses the placenta according to the mechanism of facilitated diffusion, so its concentration in the fetal blood may be higher than that of the mother. The fetus also uses liver glycogen to form glucose. Glucose is the main nutrient for the fetus. She also owns a very important role in the processes of anaerobic glycolysis.

Water. To replenish the extracellular space and volume of amniotic fluid passes through the placenta a large number of water. Water accumulates in the uterus, tissues and organs of the fetus, placenta and amniotic fluid. During physiological pregnancy, the amount of amniotic fluid increases daily by 30-40 ml. Water is essential for proper metabolism in the uterus, placenta and in the fetus. The transport of water can be carried out against the concentration gradient.

Electrolytes. The exchange of electrolytes occurs granplatsentarno and through the amniotic fluid (paraplacental). Potassium, sodium, chlorides, bicarbonates freely penetrate from mother to fetus and in the opposite direction. Calcium, phosphorus, iron and some other trace elements can be deposited in the placenta.

Vitamins. Very important the role of the placenta plays in the exchange of vitamins. She is able to accumulate them and regulates their supply to the fetus. Vitamin A and carotene are deposited in the placenta in significant amounts. In the liver of the fetus, carotene is converted into vitamin A, B vitamins accumulate in the placenta and then, binding with phosphoric acid, pass to the fetus. The placenta contains a significant amount of vitamin C. In the fetus, this vitamin in excess accumulates in the liver and adrenal glands. The vitamin D content in the placenta and its transport to the fetus depend on the vitamin D content in the mother's blood. This vitamin regulates the exchange and transport of calcium in the mother-fetus system. Vitamin E, like vitamin K, does not cross the placenta. It should be borne in mind that synthetic preparations of vitamins E and K cross the placenta and are found in the blood of the umbilical cord.

Enzymes. The placenta contains many enzymes involved in metabolism. It contains respiratory enzymes (oxidases, catalase dehydrogenases, etc.). In the tissues of the placenta there is succinate dehydrogenase, which is involved in the process of hydrogen transfer during anaerobic glycolysis. "The placenta actively synthesizes a universal source of energy ATP.

Of enzymes regulating carbohydrate metabolism, amylase, lactase, carboxylase, etc. should be mentioned. Protein metabolism is regulated by enzymes such as NAD- and NADP diaphorases. Placenta specific is the enzyme - thermostable alkaline phosphatase (TPA)... Based on the indicators of the concentration of this enzyme in the mother's blood, one can judge the function of the placenta during pregnancy. Another specific enzyme in the placenta is oxytocinase. The placenta contains a number of biologically active substances of the histamine-histaminase system, acetylcholine-cholinesterase, etc. The placenta is also rich in various factors of blood coagulation and fibrinolysis.

The structure and function of the placenta.

Placenta.

The human placenta has a hemochorial type of structure - the presence of direct contact of the maternal blood with the chorion due to a violation of the integrity of the decidual membrane of the uterus with the opening of its vessels.

Placental development. The main part of the placenta is chorionic villi - derivatives of trophoblast. In the early stages of ontogenesis, the trophoblast forms protoplasmic outgrowths consisting of cytotrophoblast cells - primary villi... Primary villi have no vessels, and the supply of nutrients and oxygen to the body of the embryo from the surrounding maternal blood occurs according to the laws of osmosis and diffusion. By the end of the 2nd week of pregnancy, connective tissue grows into the primary villi and secondary villi are formed. They are based on connective tissue, and the outer cover is represented by the epithelium - trophoblast. Primary and secondary villi are evenly distributed over the surface of the ovum.

The epithelium of the secondary villi consists of two layers:

a) cytotrophoblast (Langhans layer)- consists of cells round shape with light cytoplasm, cell nuclei are large.

b) syncytium (symplast)- the boundaries of the cells are practically indistinguishable, the cytoplasm is dark, granular, with a brush border. The nuclei are relatively small in size, spherical or oval in shape.

From the 3rd week of development of the embryo, a very important process of development of the placenta begins, which consists in the vascularization of the villi and their transformation into tertiary, containing vessels. The formation of placental vessels occurs both from the angioblasts of the embryo and from the umbilical vessels growing from allantois.

Allantois vessels grow into secondary villi, as a result of which each secondary villus becomes vascularized. The establishment of allantoid circulation provides an intensive exchange between the organisms of the fetus and the mother.

In the early stages of intrauterine development, the chorionic villi evenly cover the entire surface of the ovum. However, starting from the 2nd month of ontogenesis, on the greater surface of the ovum, the villi atrophy, at the same time, villi develop, facing the basal part of the decidua membrane. This is how a smooth and branched chorion is formed.

At a gestational age of 5-6 weeks, the thickness of the syncytiotrophoblast exceeds the thickness of the Langhans layer, and, starting from 9-10 weeks, the syncytiotrophoblast gradually becomes thinner and the number of nuclei in it increases. On the free surface of the syncytiotrophoblast, facing the intervillous space, long thin cytoplasmic outgrowths (microvilli) become clearly visible, which significantly increase the resorption surface of the placenta. At the beginning of the second trimester of pregnancy, an intensive transformation of the cytotrophoblast into syncytium occurs, as a result of which the Langhans layer completely disappears in many areas.

At the end of pregnancy, involutional-dystrophic processes begin in the placenta, which are sometimes called aging of the placenta. From the blood circulating in the intervillous space, fibrin (fibrinoid) begins to fall out, which is deposited mainly on the surface of the villi. The loss of this substance promotes the processes of microthrombus formation and the death of individual sections of the epithelial cover of the villi. The villi covered with fibrinoid are largely excluded from the active exchange between the mother and the fetus.

There is a pronounced thinning of the placental membrane. The stroma of the villi becomes more fibrous and homogeneous. Some thickening of the capillary endothelium is observed. Lime salts are often deposited in areas of dystrophy. All these changes are reflected in the functions of the placenta.

However, along with the processes of involution, there is an increase in young villi, which largely compensate for the function of the lost ones, but they only partially improve the function of the placenta as a whole. As a result, a decrease in placental function is observed at the end of pregnancy.

The structure of the mature placenta. Macroscopically, a mature placenta is very similar to a thick soft cake. The mass of the placenta is 500-600 g, diameter 15-18 cm, thickness 2-3 cm.The placenta has two surfaces:

a) maternal - facing the wall of the uterus - the placenta has a grayish-red color and is the remnants of the basal part of the decidua.

b) fruiting - facing the fetus - covered with a shiny amniotic membrane, under which the vessels coming from the place of attachment of the umbilical cord to the periphery of the placenta fit the chorion.

The main part of the fetal placenta is represented by numerous chorionic villi, which are combined into lobular formations - cotyledons, or lobules- the main structural and functional unit of the formed placenta. Their number reaches 15-20. Lobules of the placenta are formed as a result of the separation of the chorionic villi by septa (septa) emanating from the basal plate. Each of these lobules has its own large vessel.

Microscopic structure of mature villi. Distinguish two types of villi:

a) free - immersed in the intervillous space of the decidua and "float" in the maternal blood.

b) fixing (anchor) - attached to the basal decidua and provide fixation of the placenta to the wall of the uterus. In the third stage of labor, the connection of such villi with the decidua is disrupted and, under the influence of uterine contractions, the placenta is separated from the uterine wall.

With a microscopic study of the structure of a mature villi, the following formations are differentiated:

Syncytium, which does not have clear cell boundaries;

Cytotrophoblast layer (or residues);

The stroma of the villi;

The endothelium of the capillary, in the lumen of which the elements of the fetal blood are clearly visible.

Uteroplacental circulation. The blood flow of both the mother and the fetus is separated by the following structural units of the chorionic villi:

Epithelial layer (syncytium, cytotrophoblast);

Villi stroma;

Endothelium of capillaries.

Blood flow in the uterus is carried out by means of 150-200 maternal spiral arteries, which open into the vast intervillous space. The walls of the arteries are devoid of the muscle layer, and the orifices are unable to contract and expand. They have low vascular resistance to blood flow. All these features of hemodynamics have great importance in the implementation of uninterrupted transport of arterial blood from the mother's body to the fetus. The outflowing arterial blood washes the chorionic villi, while giving oxygen, essential nutrients, many hormones, vitamins, electrolytes and other chemicals, as well as trace elements necessary for the fetus to grow and develop properly, into the fetal blood. Blood containing CO 2 and other metabolic products of the fetus is poured into the venous openings of the maternal veins, total number which exceeds 180. The blood flow in the intervillous space at the end of pregnancy is quite intense and averages 500-700 ml of blood per minute.

Features of blood circulation in the mother-placenta-fetus system. The arterial vessels of the placenta after separation from the umbilical cord are divided radially in accordance with the number of placental lobes (cotyledons). As a result of further branching of the arterial vessels in the terminal villi, a network of capillaries is formed, the blood from which is collected in the venous system, the veins in which arterial blood flows, are collected in the larger venous trunks and flow into the vein of the umbilical cord.

Blood circulation in the placenta is supported by the heartbeats of the mother and fetus. An important role in the stability of this circulation also belongs to the mechanisms of self-regulation of the uteroplacental circulation.

The main functions of the placenta. The placenta performs the following main functions: respiratory, excretory, trophic, protective and endocrine. It also performs the functions of antigen formation and immune protection. An important role in the implementation of these functions is played by the membranes and amniotic fluid.

1. Respiratory function. Gas exchange in the placenta is carried out by the penetration of oxygen to the fetus and removal of CO 2 from its body. These processes are carried out according to the laws of simple diffusion. The placenta does not have the ability to accumulate oxygen and CO 2, therefore, their transport occurs continuously. Gas exchange in the placenta is similar to gas exchange in the lungs. Amniotic fluid and paraplacental metabolism play a significant role in removing CO 2 from the fetus.

2. Trophic function. The fetus is nourished by transporting metabolic products across the placenta.

Proteins. The state of protein metabolism in the mother-fetus system is determined by the protein composition of the mother's blood, the state of the protein-synthesizing system of the placenta, the activity of enzymes, the level of hormones and a number of other factors. The content of amino acids in the blood of the fetus slightly exceeds their concentration in the blood of the mother.

Lipids. The transport of lipids (phospholipids, neutral fats, etc.) to the fetus is carried out after their preliminary enzymatic breakdown in the placenta. Lipids enter the fetus in the form of triglycerides and fatty acids.

Glucose. It crosses the placenta according to the mechanism of facilitated diffusion, so its concentration in the fetal blood may be higher than that of the mother. The fetus also uses liver glycogen to form glucose. Glucose is the main nutrient for the fetus. It also plays a very important role in the processes of anaerobic glycolysis.

Water. A large amount of water passes through the placenta to replenish the extracellular space and the volume of amniotic fluid. Water accumulates in the uterus, tissues and organs of the fetus, placenta and amniotic fluid. During physiological pregnancy, the amount of amniotic fluid increases daily by 30-40 ml. Water is essential for proper metabolism in the uterus, placenta and in the fetus. The transport of water can be carried out against the concentration gradient.

Electrolytes. The exchange of electrolytes occurs transplacentally and through the amniotic fluid (paraplacental). Potassium, sodium, chlorides, bicarbonates freely penetrate from mother to fetus and in the opposite direction. Calcium, phosphorus, iron and some other trace elements can be deposited in the placenta.

Vitamins. Vitamin A and carotene are deposited in the placenta in significant amounts. In the liver of the fetus, carotene is converted into vitamin A. Vitamins of group B accumulate in the placenta and then, binding with phosphoric acid, pass to the fetus. The placenta contains a significant amount of vitamin C. In the fetus, this vitamin in excess accumulates in the liver and adrenal glands. The vitamin D content in the placenta and its transport to the fetus depend on the vitamin D content in the mother's blood. This vitamin regulates the exchange and transport of calcium in the mother-fetus system. Vitamin E, like vitamin K, does not cross the placenta.

3. Endocrine function. In the physiological course of pregnancy, there is a close relationship between the hormonal status of the mother's body, the placenta and the fetus. The placenta has a selective ability to transfer maternal hormones. Hormones with a complex protein structure (growth hormone, thyroid-stimulating hormone, ACTH, etc.) practically do not cross the placenta. The penetration of oxytocin through the placental barrier is prevented by the high activity in the placenta of the enzyme oxytocinase. Steroid hormones have the ability to cross the placenta (estrogens, progesterone, androgens, glucocorticoids). The mother's thyroid hormones also cross the placenta, however, the transplacental transition of thyroxine occurs more slowly than triiodothyronine.

Along with the function of transforming maternal hormones, the placenta itself turns into a powerful endocrine organ during pregnancy, which ensures the presence of optimal hormonal homeostasis in both the mother and the fetus.

One of the most important placental hormones of a proteinaceous nature is placental lactogen(PL). In its structure, PL is close to the growth hormone of the adenohypophysis. The hormone almost entirely enters the maternal bloodstream and takes an active part in carbohydrate and lipid metabolism. In the blood of a pregnant woman, PL begins to be detected very early - from the 5th week, and its concentration progressively increases, reaching a maximum at the end of gestation. PL practically does not penetrate the fetus, and it is contained in the amniotic fluid in low concentrations. This hormone is given an important role in the diagnosis of placental insufficiency.

Another hormone of the placenta of protein origin is chorionic gonadotropin(XG). HCG in the mother's blood is detected in the early stages of pregnancy, the maximum concentrations of this hormone are observed at 8-10 weeks of pregnancy. It passes to the fruit in limited quantities. Hormonal pregnancy tests are based on the determination of HCG in blood and urine: immunological reaction, Aschheim-Tsondek reaction, hormonal reaction on male frogs .

The placenta, along with the pituitary gland of the mother and the fetus, produces prolactin. The physiological role of placental prolactin is similar to that of the PL of the pituitary gland.

Estrogens(estradiol, estrone, estriol) are produced by the placenta in increasing quantities, with the highest concentrations of these hormones observed before childbirth. About 90% of the placental estrogen is represented by estriol. Its content reflects not only the function of the placenta, but also the condition of the fetus.

Important place in the endocrine function of the placenta belongs to the synthesis progesterone... The production of this hormone begins from the early stages of pregnancy, however, during the first 3 months, the main role in the synthesis of progesterone belongs to the corpus luteum, and only then the placenta takes on this role. From the placenta, progesterone enters mainly the mother's bloodstream and, to a much lesser extent, into the fetal bloodstream.

A glucocorticoid steroid is produced in the placenta cortisol. This hormone is also produced in the adrenal glands of the fetus, so the concentration of cortisol in the mother's blood reflects the state of both the fetus and the placenta (fetoplacental system).

4. Barrier function of the placenta. The term "placental barrier" includes the following histological formations: syncytiotrophoblast, cytotrophoblast, layer of mesenchymal cells (stroma of villi) and endothelium of the fruit capillary. It is characterized by the transition of various substances in two directions. Placental permeability is variable. In physiological pregnancy, the permeability of the placental barrier progressively increases up to the 32-35th week of pregnancy, and then slightly decreases. This is due to the structural features of the placenta at different stages of pregnancy, as well as the needs of the fetus in certain chemical compounds. The limited barrier function of the placenta in relation to chemicals that accidentally entered the mother's body is manifested in the fact that toxic products of chemical production, most drugs, nicotine, alcohol, pesticides, infectious agents, etc. pass through the placenta relatively easily. The barrier functions of the placenta are most fully manifested only under physiological conditions, i.e. with uncomplicated pregnancy. Under the influence of pathogenic factors (microorganisms and their toxins, sensitization of the mother's body, the effects of alcohol, nicotine, drugs), the barrier function of the placenta is disrupted, and it becomes permeable even for substances that, under normal physiological conditions, pass through it in limited quantities.

The placenta performs the following main functions: respiratory, excretory, trophic, protective and endocrine. It also performs the functions of antigen formation and immune defense. An important role in the implementation of these functions is played by the membranes and amniotic fluid.

The transfer of chemical compounds through the placenta is determined by various mechanisms: ultrafiltration, simple and facilitated diffusion, active transport, pinocytosis, transformation of substances in the chorionic villi. The solubility of chemical compounds in lipids and the degree of ionization of their molecules are also of great importance.

Ultrafiltration processes depend on the molecular weight of the chemical. This mechanism takes place in cases where the molecular weight does not exceed 100. At a higher molecular weight, a difficult transplacental transition is observed, and with a molecular weight of 1000 or more, chemical compounds practically do not pass through the placenta, therefore their transition from mother to fetus is carried out with the help of other mechanisms.

The diffusion process consists in the transfer of substances from an area of ​​higher concentration to an area of ​​lower concentration. This mechanism is typical for the transfer of oxygen from the mother's body to the fetus and CO2 from the fetus to the mother's body. Facilitated diffusion differs from simple diffusion in that the equilibrium of the concentrations of chemical compounds on both sides of the placental membrane is achieved much faster than could be expected based on the laws of simple diffusion. Such a mechanism has been proven for the transition from the mother to the fetus of glucose and some other chemicals.

Pinocytosis is a type of transition of a substance through the placenta, when the chorionic villi actively absorb droplets of the mother's plasma, along with certain compounds contained in them.

Along with these mechanisms of transplacental metabolism, solubility in lipids and the degree of ionization of molecules of chemical agents are of great importance for the transfer of chemicals from the mother's body to the fetus and in the opposite direction. The placenta functions as a lipid barrier. This means that chemicals that are readily soluble in lipids cross the placenta more actively than those that are poorly soluble. The role of ionization of molecules of a chemical compound is that undissociated and non-ionized substances cross the placenta more quickly.

The size of the exchange surface of the placenta and the thickness of the placental membrane are also essential for the exchange processes between the organisms of the mother and the fetus.

Despite the phenomenon of so-called physiological aging, placental permeability progressively increases up to the 32-35th week of pregnancy. This is mainly due to an increase in the number of newly formed villi, as well as a progressive thinning of the placental membrane itself (from 33-38 microns at the beginning of pregnancy to 3-6 microns at the end of it).

The degree of transition of chemical compounds from the mother's body to the fetus depends not only on the characteristics of the placenta permeability. A large role in this process belongs to the organism of the fetus itself, its ability to selectively accumulate precisely those agents that are in this moment especially necessary for him for growth and development. So, during the period of intense hematopoiesis, the fetus's need for iron increases, which is necessary for the synthesis of hemoglobin. If the mother's body contains an insufficient amount of iron, then she becomes anemic. With intensive ossification of the bones of the skeleton, the fetus's need for calcium and phosphorus increases, which causes an increased transplacental transfer of their salts. During this period of pregnancy, the mother's processes of depletion of her body with these chemical compounds are especially pronounced.

Respiratory function of the placenta

Gas exchange in the placenta is carried out by the penetration of oxygen to the fetus and removal of CO2 from its body. These processes are carried out according to the laws of simple diffusion. The placenta does not have the ability to accumulate oxygen and CO2, so they are transported continuously. Gas exchange in the placenta is similar to gas exchange in the lungs. Amniotic fluid and paraplacental metabolism play a significant role in removing CO2 from the fetus.

Trophic function of the placenta

The fetus is nourished by transporting metabolic products across the placenta.

Proteins. The state of protein metabolism in the mother-fetus system is determined by many factors: the protein composition of the mother's blood, the state of the protein-synthesizing system of the placenta, the activity of enzymes, the level of hormones and a number of other factors. The placenta has the ability to deaminate and transaminate amino acids, synthesize them from other precursors. This causes the active transport of amino acids into the blood of the fetus. The content of amino acids in the blood of the fetus slightly exceeds their concentration in the blood of the mother. This indicates an active role of the placenta in protein metabolism between the mother and the fetus. The fetus synthesizes its own proteins from amino acids, which are immunologically different from those of the mother.

Lipids. The transport of lipids (phospholipids, neutral fats, etc.) to the fetus is carried out after their preliminary enzymatic breakdown in the placenta. Lipids enter the fetus in the form of triglycerides and fatty acids. Lipids are mainly localized in the cytoplasm of the syncytium of the chorionic villi, thereby ensuring the permeability of the cell membranes of the placenta.

Glucose. It crosses the placenta according to the mechanism of facilitated diffusion, so its concentration in the fetal blood may be higher than that of the mother. The fetus also uses liver glycogen to form glucose. Glucose is the main nutrient for the fetus. It also plays a very important role in the processes of anaerobic glycolysis.

Water. A large amount of water passes through the placenta to replenish the extracellular space and the volume of amniotic fluid. Water accumulates in the uterus, tissues and organs of the fetus, placenta and amniotic fluid. During physiological pregnancy, the amount of amniotic fluid increases daily by 30-40 ml. Water is essential for proper metabolism in the uterus, placenta and in the fetus. The transport of water can be carried out against the concentration gradient.

Electrolytes. The exchange of electrolytes occurs transplacentally and through the amniotic fluid (paraplacental). Potassium, sodium, chlorides, bicarbonates freely penetrate from mother to fetus and in the opposite direction. Calcium, phosphorus, iron and some other trace elements can be deposited in the placenta.

Vitamins. The placenta plays a very important role in the metabolism of vitamins. She is able to accumulate them and regulates their supply to the fetus. Vitamin A and carotene are deposited in the placenta in significant amounts. In the liver of the fetus, carotene is converted into vitamin A. Vitamins of group B accumulate in the placenta and then, binding with phosphoric acid, pass to the fetus. The placenta contains a significant amount of vitamin C. In the fetus, this vitamin in excess accumulates in the liver and adrenal glands. The vitamin D content in the placenta and its transport to the fetus depend on the vitamin D content in the mother's blood. This vitamin regulates the exchange and transport of calcium in the mother-fetus system. Vitamin E, like vitamin K, does not cross the placenta. It should be borne in mind that synthetic preparations of vitamins E and K cross the placenta and are found in the blood of the umbilical cord.

Enzymes. The placenta contains many enzymes involved in metabolism. It contains respiratory enzymes (oxidases, catalase, dehydrogenases, etc.). In the tissues of the placenta, there is succinate dehydrogenase, which is involved in the process of hydrogen transfer during anaerobic glycolysis. The placenta actively synthesizes the universal energy source ATP.

Of the enzymes that regulate carbohydrate metabolism, amylase, lactase, carboxylase, etc. should be indicated. Protein metabolism is regulated by enzymes such as NAD- and NADP diaphorases. An enzyme specific to the placenta is thermostable alkaline phosphatase (TPA). Based on the indicators of the concentration of this enzyme in the mother's blood, one can judge the function of the placenta during pregnancy. Another specific enzyme in the placenta is oxytocinase. The placenta contains a number of biologically active substances of the histamine-histaminase system, acetylcholine-cholinesterase, etc. The placenta is also rich in various factors of blood coagulation and fibrinolysis.

Endocrine function of the placenta

In the physiological course of pregnancy, there is a close relationship between the hormonal status of the mother's body, the placenta and the fetus. The placenta has a selective ability to transfer maternal hormones. So, hormones with a complex protein structure (somatotropin, thyroid-stimulating hormone, ACTH, etc.) practically do not cross the placenta. The penetration of oxytocin through the placental barrier is prevented by the high activity in the placenta of the enzyme oxytocinase. The transfer of insulin from the mother to the fetus appears to be hindered by its high molecular weight.

In contrast, steroid hormones have the ability to cross the placenta (estrogens, progesterone, androgens, glucocorticoids). The mother's thyroid hormones also cross the placenta, however, the transplacental transition of thyroxine occurs more slowly than triiodothyronine.

Along with the function of transforming maternal hormones, the placenta itself turns into a powerful endocrine organ during pregnancy, which ensures the presence of optimal hormonal homeostasis in both the mother and the fetus.

One of the most important placental hormones of a proteinaceous nature is the placental lactogen (PL). In its structure, PL is close to the growth hormone of the adenohypophysis. The hormone almost entirely enters the maternal bloodstream and takes an active part in carbohydrate and lipid metabolism. In the blood of a pregnant woman, PL begins to be detected very early - from the 5th week, and its concentration progressively increases, reaching a maximum at the end of gestation (Fig. 3.11, a). PL practically does not penetrate the fetus, and it is contained in the amniotic fluid in low concentrations. This hormone is given an important role in the diagnosis of placental insufficiency.

Another protein-derived placental hormone is human chorionic gonadotropin (HCG). In terms of its structure and biological action, hCG is very similar to the luteinizing hormone of the adenohypophysis. During the dissociation of CG, two subunits (a and p) are formed. The function of the placenta most accurately reflects p-hCG. HCG in the mother's blood is detected in the early stages of pregnancy, the maximum concentrations of this hormone are observed at 8-10 weeks of pregnancy. In the early stages of pregnancy, hCG stimulates steroidogenesis in the corpus luteum of the ovary, in the second half - the synthesis of estrogens in the placenta. HG passes to the fetus in limited quantities. CG is believed to be involved in the mechanisms of fetal sexual differentiation. Hormonal pregnancy tests are based on the determination of HCG in blood and urine: immunological reaction, Ashheim-Tsondek reaction, hormonal reaction on male frogs, etc.

The placenta, along with the pituitary gland of the mother and the fetus, produces prolactin. The physiological role of placental prolactin is similar to that of the PL of the pituitary gland.

In addition to protein hormones, the placenta synthesizes sex steroid hormones (estrogens, progesterone, cortisol).

Estrogens (estradiol, estrone, estriol) are produced by the placenta in increasing quantities, with the highest concentrations of these hormones observed before childbirth. About 90% of placental estrogens are estriol. Its content reflects not only the function of the placenta, but also the condition of the fetus. The fact is that estriol in the placenta is formed from androgens of the adrenal glands of the fetus, therefore, the concentration of estriol in the mother's blood reflects the state of both the fetus and the placenta. These features of estriol production formed the basis of the endocrine theory of the fetoplacental system.

Estradiol is also characterized by a progressive increase in concentration during pregnancy. Many authors believe that it is this hormone that is decisive in preparing the body of a pregnant woman for childbirth.

An important place in the endocrine function of the placenta belongs to the synthesis of progesterone. The production of this hormone begins early in pregnancy, but during the first 3 months. the main role in the synthesis of progesterone belongs to the corpus luteum, and only then the placenta takes on this role. From the placenta, progesterone enters mainly the mother's bloodstream and, to a much lesser extent, into the fetal bloodstream.

The placenta produces the glucocorticoid steroid cortisol. This hormone is also produced in the adrenal glands of the fetus, so the concentration of cortisol in the mother's blood reflects the state of both the fetus and the placenta (fetoplacental system).

Until now, the question of the production of ACTH and TSH by the placenta remains open.

Placental immune system. The placenta is a kind of immune barrier that separates two genetically foreign organisms (mother and fetus), therefore, during a physiologically proceeding pregnancy, an immune conflict between the organisms of the mother and the fetus does not arise. The absence of an immunological conflict between the organisms of the mother and the fetus is due to the following mechanisms:

• the absence or immaturity of the antigenic properties of the fetus;
• the presence of an immune barrier between the mother and the fetus (placenta);
• immunological characteristics of the mother's body during pregnancy.

Placenta barrier function

The term "placental barrier" includes the following histological formations: syncytiotrophoblast, cytotrophoblast, layer of mesenchymal cells (stroma of villi) and endothelium of the fruit capillary. The placental barrier can, to some extent, be likened to the blood-brain barrier, which regulates the penetration of various substances from the blood into the cerebrospinal fluid. However, unlike the blood-brain barrier, the selective permeability of which is characterized by the transfer of various substances in only one direction (blood - cerebrospinal fluid), the placental barrier regulates the transfer of substances in the opposite direction, i.e. from fetus to mother.

The transplacental transition of substances that are constantly in the mother's blood and that have fallen into it by accident is subject to different laws. The transition from mother to fetus of chemical compounds that are constantly present in the mother's blood (oxygen, proteins, lipids, carbohydrates, vitamins, trace elements, etc.) is regulated by fairly precise mechanisms, as a result of which some substances are contained in the mother's blood in higher concentrations than in the blood of the fetus, and vice versa. In relation to substances that accidentally entered the maternal organism (agents of chemical production, drugs, etc.), the barrier functions of the placenta are expressed to a much lesser extent.

Placental permeability is variable. In physiological pregnancy, the permeability of the placental barrier progressively increases up to the 32-35th week of pregnancy, and then slightly decreases. This is due to the structural features of the placenta at different stages of pregnancy, as well as the needs of the fetus in certain chemical compounds.

The formal barrier functions of the placenta in relation to chemicals that accidentally entered the mother's body are manifested in the fact that toxic products of chemical production, most drugs, nicotine, alcohol, pesticides, infectious agents, etc. pass through the placenta relatively easily. This creates a real danger for the adverse effects of these agents on the embryo and fetus.

The barrier functions of the placenta are most fully manifested only under physiological conditions, i.e. with uncomplicated pregnancy. Under the influence of pathogenic factors (microorganisms and their toxins, sensitization of the mother's body, the effects of alcohol, nicotine, drugs), the barrier function of the placenta is disrupted, and it becomes permeable even for substances that, under normal physiological conditions, pass through it in limited quantities.

Ed. G. Savelyeva

"What functions does the placenta perform" - an article from the section

The placenta provides normal respiration, nutrition of the fetus and the elimination of decay products from the formation of the placenta. During pregnancy, it replaces the functions of the lungs, digestive organs, kidneys, skin, etc.

Placenta formation and development during pregnancy

The placenta looks like a round, thick and soft "cake". At the time of delivery, the diameter of the placenta reaches 15-18 cm, and its thickness is 2-3 cm, while the weight is 500-600 g. As already noted, the placenta has two surfaces:

• maternal, adjacent to the wall of the uterus,
• and fruit, facing inward into the amnion cavity.

The fruit surface is covered with a smooth water membrane, under which vessels extend to the chorion, extending radially from the place of attachment of the umbilical cord to the periphery of the placenta.

In turn, the maternal surface of the placenta is grayish-red in color, divided by more or less deep grooves into lobules, consisting of many branching villi, in which blood vessels are located - cotyledons. The presence of a grayish tint is associated with the color of the decidua covering the overgrown villi. As a rule, attachment of the placenta is noted in the upper part of the uterus on the anterior or posterior wall; attachment in the region of the fundus or tubal corners is very rare.

The role of villi in the formation of the placenta during pregnancy

The formation of the placenta is carried out from the basal part of the decidua and strongly overgrown villous chorionic villi. The bulk of the placenta is represented by highly branching chorionic villi. Vessels passing through large villi divide as the villi branch. In the terminal villi, only capillary loops pass. The number of villi increases with the duration of pregnancy. The formation of the placenta provides an increase in the boundary surface of contact between the blood flow of the mother and the fetus. This boundary surface, which determines the state of gas exchange, nutrition and excretion of metabolic products of the fetus, in the mature placenta significantly exceeds the surface of the body of an adult. The total surface area of ​​all villi in a mature placenta is 6–10 m². The length of the villi folded longitudinally is more than 50 km.

During the development of the placenta, some villi grow together with maternal tissues and are anchorage (anchor). Most of the villi are located freely, they are immersed directly in the blood circulating in the intervillous space. In terms of structure, the villi are represented by a layer of protoplasmic mass (outer cover), which does not have cell membranes. The nuclei are freely located in it, and this layer is called syncytium (plasmodiotrophoblast). On the surface of the syncytium there are microscopic villi, which can only be detected by an electron microscope, which further increase the resorption capacity of the villi. It should be noted that the work of syncytium is enormous, it processes a large amount of nutrients supplied to the fetus from the mother's body. As already noted, syncytium plays an important role in the process of implantation of the ovum due to the presence of various kinds of enzymes in it.

The next layer of villi is represented by the chorionic epithelium - cytotrophoblast. In the first months of pregnancy, the cytotrophoblast forms a continuous layer, and later its individual cells gradually disappear. Therefore, the villi almost completely lose their cytotrophoblast in the second half of pregnancy. In addition to participating in metabolism, complex enzymatic processes and synthesis of hormones take place in the cytotrophoblast, and it is also a germ layer for syncytium. Capillaries pass in the very center of the villi.

Placenta functions during pregnancy

The maternal part of the placenta is represented by a thickened part of the decidua, located under the overgrown chorionic villi (fruit part of the placenta). In this part of the placenta, depressions are formed, into which the villi are immersed and where the maternal blood that washes them circulates. Between these recesses there are protrusions (partitions) of the decidual tissue, to which the anchor villi are attached. In the structure of these septa there are arteries that bring maternal blood to the intervillous spaces.

The ability to drain blood from these arteries is provided by the enzymatic activity of the trophoblast syncytium. In turn, venous blood from the intervillous spaces is diverted through the marginal sinus of the placenta and the veins of the uterus. Since blood circulation in the intervillous spaces is slow, nutrients can be fully absorbed. It should be noted that the incoagulability of the blood washing the villi also contributes to good absorption. It does not mix with fetal blood flowing inside the villous vessels. In addition to the consumption of nutrients and oxygen, metabolic products and carbon dioxide of the fetus enter the mother's blood, which must be removed from the fetus's body.

Thus, the placenta is an indispensable organ for performing the function of respiration, excretion of metabolic products and the supply of nutrients for the fetus.

I would like to note that metabolic processes occur in the placenta more intensively in the early stages of its development. This is evident from the significant content in the syncytium and cytotrophoblast

• nucleic acids,
• mitochondria,
• lysosomes, etc.,
• as well as enzymes that carry out redox processes that break down proteins, carbohydrates, lipids.

Intrasecretory functions of the placenta

Among other things, the role of the placenta in the intrasecretory function is important. In the cytotrophoblast, chorionic gonadotropin is synthesized, the amount of which especially increases by early dates pregnancy. The production of gonadotropin lasts for several months. Together with placental prolactin, chorionic gonadotropin promotes the development and functional activity of the corpus luteum of pregnancy. Also, synthesis occurs in the placenta

• chorionic somatotropin (somatotropic placental lactogen),
• estrogenic hormones, mainly estriol.

The entire synthesis process takes place in syncytium and trophoblast. During pregnancy, hormones are synthesized unevenly, for example, estrogen synthesis rises sharply in the second half of pregnancy. At the end of pregnancy, the formation of fractions (estriol, estrone) is noted in the placenta, which increase the excitability and contractile activity of the uterus. In turn, starting from the third, fourth month of pregnancy, progesterone is formed in the placenta. This process coincides with the termination of the intrasecretory function of the corpus luteum of pregnancy, and the placenta begins to perform the function of this gland (synthesis of progesterone). There is evidence of the release of cortisol, adrenocorticotropic, thyroid-stimulating and other hormones from the tissue of the placenta, however, their synthesis in the placenta has not been proven. According to the same data, oxytocin, vasopressin, histamine, acetylcholine, prostaglandins were found in the tissue of the placenta.

It was also revealed that the placenta contains group specific antigens, and the antigens contained in the amnion and chorion correspond to the fetal blood group. The placenta also contains blood coagulation and fibrinolysis factors (thromboplastin, fibrinolysins, calcium, etc.), which promotes proper blood circulation in the intervillous space and stops bleeding after childbirth (thromboplastin is released from the placenta).

Placental permeability and its function in the development of pregnancy

Let us dwell separately on the permeability of the placenta for various kinds of substances. The ability of the chorionic epithelium of the villi to pass certain substances to the fetus and not let others pass through was noted. For example, trypan blue, Congo red, curare and many other substances do not pass to the fetus. There is also information that, for example, bromine passes from the mother to the fetus faster than in the opposite direction, fluoride also enters the fetus, but its reverse passage through the placenta is inhibited.

Placenta barrier function during pregnancy

As a result of such data, it was concluded that there are barrier functions of the placenta, that is, the ability to delay the transition to the fetus of substances that are not required or harmful to the fetus. In this regard, there is an opinion that the placenta inhibits the transition of microbes, including pathogenic ones. Nevertheless, some pathogens of infectious diseases, viruses, protozoa (toxoplasma), pathogenic and non-pathogenic coccal flora and other microorganisms still pass to the fetus. The transfer of microbes is usually facilitated by changes in the placenta that occur during the illness of a pregnant woman.

Nevertheless, the barrier function of the placenta is limited to certain limits. It was found that through the placenta into the blood of the fetus penetrate

• ether,
• nitrous oxide and other gases,
• alcohol
• , morphine,
• atropine,
• pantopon and other drugs,
• chloral hydrate,
• Mercury,
• arsenic,
• nicotine,
• sulfonamides,
• antibiotics,
• barbiturates,
• salicylates,
• cardiac glycosides,
• quinine, etc.

Most of the list of these substances have severe toxic or harmful effects. The possibility of transfer of erythrocytes and leukocytes of the fetus into the mother's blood has been proven, but only in limited quantities. When prescribing drugs, it is imperative to remember that almost all pharmacological drugs prescribed for pregnant women, as well as pain relievers during childbirth, penetrate into the fetus.

The function of the "mother - placenta - fetus" system during the formation and course of pregnancy

Immediately after conception, the mother-placenta-fetus system appears. It is directed "mother - placenta - fetus" to maintain optimal conditions for the development of the embryo, and then the fetus in the body and is associated with complex and interdependent adaptation processes. For the first time, the doctrine of functional systems was proposed by PK Anokhin in the 30s – 60s. XX century Then he defined the functional system as a dynamic, self-regulating organization, selectively combining structures and processes based on nervous and humoral mechanisms of regulation to achieve adaptive results that are important for the system and the body as a whole. The functional system has a branched apparatus, which, due to its inherent regularities, provides the effect of both homeostasis and self-regulation.

From a physiological point of view, the very concept of a "functional system" carries not only the simple coexistence of its individual elements, but also their mutually regulating and interdependent assistance.

Normal development of the central nervous system of the fetus is impossible without the presence of afferent impulses from the heart, which is the first working organ in the fetus. And after the ninth week, when motor reactions of the fetus appear, impulses are received from the receptors of skeletal muscles. In turn, after the onset of respiratory movements (twelfth week of pregnancy), impulses into the respiratory centers of the fetus begin.

The pathology of underdevelopment of the fetal muscular system occurs due to a lack of fetal motor activity, which in turn is combined with insufficient impulses to the central nervous system. All this leads to a slowdown in the development of centers that regulate the activity of muscles (including respiratory), and disruption of many other functions of the developing fetus. All life support systems required after the birth of the fetus are formed before birth, they also undergo special checks for readiness and training.

Features of the "mother - placenta - fetus" system during pregnancy

Based on this, the functional system "mother - placenta - fetus" has a number of features:

the period of existence of this functional system is limited by the period of pregnancy, that is, directly by the time of development of the embryo and fetus until the moment of birth;

this functional system can be formed only in a woman's body with all its physiological characteristics;

during the formation and formation of the functional system mother - placenta - fetus, both normal anatomical and physiological processes and pathological processes are involved, which are also necessary for the progression of the gestational process and the development of the fetus (invasive growth of trophoblast, gestational changes in the spiral arteries, etc.);

during the formation and existence of this functional system, there are certain "critical periods" that determine either its very further existence, or significant deviations in the normal development of the fetus;

the ultimate goal of the functional system mother - placenta - fetus is not only the birth of a living and viable child, but also the optimal adaptation of the mother's body to the gestational process (i.e., the physiological course of pregnancy).

Formation of blood flow in the placenta during pregnancy

As already noted, all the processes associated with the functioning of the mother-placenta-fetus system are aimed not only at the normal formation of all fetal systems, but also at the full adaptation of the mother's body. It should be noted that the entire sequence of the formation and further functioning of this system is genetically programmed. For example, the receipt of oxygen from the outside is provided by the hemodynamic functional system "mother - placenta - fetus", which is a subsystem of the general functional system mother - fetus. Its development occurs first in the earliest period of ontogenesis. In it, fetoplacental and uteroplacental blood circulation is simultaneously formed.

Two blood flows in the placenta can be distinguished:

the flow of maternal blood flowing through the hemodynamics of blood in the mother's body;

the blood flow of the fetus, depending on the reactions of its cardiovascular system.

During pregnancy, the flow of blood to the placenta is heterogeneous, the greatest blood flow is observed towards the end of pregnancy. The main point of blood supply to the placenta is the contraction of the myometrium. Therefore, in pathological conditions (increased tone of the myometrium, the threat of spontaneous miscarriage or premature birth), there is a decrease in blood flow to the placenta, and, consequently, to the fetus, which can cause disturbances in the normal development of the fetus.

Endocrine function of the mother-placenta-fetus system during pregnancy

The endocrine function of the mother-placenta-fetus system has a definite and rather complex development. It is possible to consider this whole process using the example of estriol synthesis. Initially, all the enzyme systems required for the production of estrogens are distributed between the fetus (its adrenal glands and liver), the placenta, and the mother's adrenal glands.

The first step in estrogen biosynthesis occurs during pregnancy in the placenta by hydroxylating the cholesterol molecule. The resulting pregnenolone from the placenta enters the adrenal glands of the fetus, where it is transformed into dehydroepiandrosterone (DEA). DEA subsequently enters the venous blood back to the placenta, where, under the influence of certain enzyme systems, it undergoes aromatization and is converted into estrone and estradiol. In the future, an even more complex hormonal exchange between the body of the mother and the fetus converts these compounds into estriol (the main estrogen of the fetoplacental complex).

Placental separation and function during pregnancy

In the subsequent period of labor, the placenta and membranes are separated from the walls of the uterus and the placenta is born. The separation of the placenta occurs as a result of 2-3 contractions and attempts of a woman for 10 minutes. The immediate duration of this period should not exceed 30 minutes.

The separation of the placenta occurs due to the contraction of the uterus, including the placental site (the place of attachment of the placenta). Since the placenta does not have the ability to contract, it is separated from the placental site. Abruption of the placenta leads to the formation of a retroplacental hematoma (since the integrity of the vessels is violated), which is an accumulation of blood between the placenta and the wall of the uterus.

Retroplacental hematoma and continued uterine contractions lead to complete detachment of the placenta. The separated afterbirth by force of efforts is born. The placenta leaves the genital tract with the amniotic membrane outward. The pathway described above for detachment of the placenta is called the "central pathway" (first described by Schultz).

However, during the subsequent period of labor, there may be a peripheral pathway of placental abruption, when the separation begins not from the center, but from the periphery. In this case, a retroplacental hematoma does not form, and the blood, flowing down, exfoliates the membranes. Plus, its own mass contributes to the entire department of the placenta. The afterbirth is born anteriorly by the lower edge of the placenta (maternal surface), and the amniotic membrane is inside. This process is called Duncan separation of the placenta.