Placenta and placental barrier. The immune system of the placenta. Barrier function of the placenta

Today, the term "placenta" no longer surprise anyone. Modern girls are much better informed about pregnancy and childbirth than their grandmothers and mothers. However, most of this knowledge is superficial. Therefore, today we want to talk about what the placental barrier is in the womb. At first glance, what's incomprehensible here? The child's place has properties to protect developing embryo from harmful effects and toxic substances. In fact, this organ is a real mystery and a miracle of nature.

under protection

Placental barrier It is a kind of immune system. It serves as a boundary between two organisms. It is the placenta that ensures their normal coexistence and the absence of an immunological conflict. The first trimester of pregnancy is the most difficult. Partly because the placenta is not yet formed, which means that the body of the embryo is completely unprotected. From about 12 weeks, she is fully included in the work. From now on, she is ready to perform all her functions.

How is the placenta arranged?

This important point, without which we will not be able to continue our conversation. The very word "placenta" came to us from Latin. It translates as "cake". Its main part is special villi, which begin to form from the first days of pregnancy. Every day they branch out more and more. At the same time, inside them is the blood of the child. At the same time, maternal blood enriched with nutrients enters from the outside. That is, the placental barrier primarily has a separating function. This is very important, since this organ regulates the exchange of substances between two closed systems. According to this statement, the external and inner side placenta has different structure. Inside it is smooth. Outer side- uneven, lobed.

barrier function

What does the concept of "placental barrier" include? Let's deviate a little more towards the physiology of the ongoing processes. As already mentioned, it is the unique villi that provide the exchange of substances between the woman and the embryo. Maternal blood brings oxygen to the baby and the fetus gives carbon dioxide to the pregnant girl. while they have one for two. And therein lies the greatest mystery. The placental barrier separates maternal and fetal blood so well that they do not mix.

At first glance it seems unimaginable, but two vascular systems separated by a unique membrane partition. It selectively skips what is important for the development of the fetus. On the other hand, toxic, harmful and dangerous substances linger here. Therefore, doctors say that starting from 12 weeks expectant mother you can relax a little. The placenta is able to protect the body of the child from many adverse factors.

Only the most important

All necessary nutrients and oxygen pass through the placental barrier. If the doctor observes the pathology of fetal development, he may prescribe special drugs that increase the blood supply to the placenta. This means that they increase the amount of oxygen that enters the baby. However, not all so simple. The membrane septum retains the bacteria and viruses contained in the mother's blood, as well as antibodies that are produced during the Rhesus conflict. That is, the unique structure of this membrane is tuned to preserve the fetus in a variety of situations.

It should be noted the high selectivity of the partition. The same substances that have got through the placental barrier overcome this boundary in different ways in the direction of the mother and fetus. For example, fluorine very easily and quickly penetrates from a woman to a baby, but does not pass back at all. The situation is similar with bromine.

What regulates metabolism?

We have already told the reader that the placental barrier separates the maternal and fetal lymph. How did nature manage to launch such a perfect mechanism of regulation, when what is needed penetrates the barrier, and what is harmful is delayed? In fact, we are talking about two mechanisms here at once. Next, let's take a closer look at each of them.

First of all, we are interested in how the supply of vital, nutrient elements is regulated. Everything is quite simple here. Lipids and carbohydrates, proteins and vitamins are constantly present in the mother's blood. This means that the body can develop a balanced scheme. It will initially imply that the concentration of certain substances in the blood of the mother and child is different.

placental permeability

It is much more difficult when we are talking about toxic substances that enter the body of a pregnant woman. The placental barrier separates lymph and blood. This means that those toxins that have passed through the mother's bloodstream will not get into pure form to the fetus. However, after passing through the natural filters (liver and kidneys) in a residual form, they can still harm the baby. The fact is that substances (chemicals, drugs) that accidentally enter the mother's body are much more difficult to stop. They often tend to overcome the placental barrier.

Limited barrier functions

Nature could not foresee the development of modern industry. Therefore, the products of chemical production relatively easily pass the natural barrier. They pose a threat to the growth and development of the fetus. The degree of penetration through the placenta depends on the properties and characteristics of a particular substance. We will only mention a few points, in fact there are many more. Thus, medicinal substances with a molecular weight (less than 600 g / mol) pass through the placental barrier much faster. At the same time, those that have a lower rate practically do not penetrate. For example, these are insulin and heparin, which can be prescribed without fear during pregnancy.

There is another sign. Fat-soluble substances cross the placenta much better than water-soluble ones. Therefore, hydrophilic compounds are more desirable. In addition, physicians know that the probability of penetration of a substance through the placenta depends on the residence time of the drug in the blood. All medications long-acting are more dangerous than those that are rapidly metabolized.

PLACENTAL BARRIER

placental barrier, blood-tissue barrier that regulates penetration various substances from mother's blood to fetal blood and vice versa. Functions P. b. are aimed at protecting the internal environment of the fetus from the penetration of substances circulating in the mother's blood that do not have energetic and plastic significance for the fetus, as well as protecting the mother's internal environment from the penetration of substances that violate it from the fetal blood. P. b. consists of the epithelium of the trophoblast, syncytium covering the villi of the chorion of the placenta, the connective tissue of the villi and the endothelium of their capillaries. In the terminal villi, many capillaries are located just below the syncytium, and P. b. at the same time they consist of 2 unicellular membranes. It has been established that substances with a molecular weight below 350 can mainly enter the blood of the fetus from the mother's body. There are also data on the passage through P. b. macromolecular substances, antibodies, antigens, as well as viruses, bacteria, helminths. The penetration of macromolecular substances, antigens, bacteria is observed in the pathology of pregnancy, since the function P. b. is violated. P. b. is selectively permeable and in relation to substances with a molecular weight below 350. So, through P. b. acetylcholine, histamine, adrenaline cannot penetrate. Function P. b. in this case, it is carried out with the help of special enzymes that destroy these substances. In the pathology of pregnancy, many medicinal substances, as well as products of impaired metabolism, penetrate the blood of the fetus and have a damaging effect on it. See also .

Veterinary encyclopedic dictionary. - M.: "Soviet Encyclopedia". Chief editor V.P. Shishkov. 1981 .

See what the "PLACENTAL BARRIER" is in other dictionaries:

placental barrier- ANIMAL EMBRYOLOGY PLACENTAL BARRIER - a histohematological barrier that regulates the penetration of various substances from the mother's blood into the fetal blood and vice versa. It consists of the epithelium of the trophoblast, syncytium, covering the villi of the chorion of the placenta, ... ...

placental barrier- a set of morphological and functional features placenta, which determine its ability to selectively pass substances from the mother's blood to the fetus and vice versa ... Big Medical Dictionary

Placental barrier- - a set of morphological and functional features of the placenta, providing the ability to selectively pass certain substances from the mother's blood to the fetus, subject them to biological processing and retain them from the fetus to the mother ... Glossary of terms for the physiology of farm animals

place barrier- ANIMAL EMBRYOLOGY PLACED BARRIER - a barrier between the mother and the fetus, consisting of the trophoblast, the basal lamina underlying it, the connective tissue lying between the trophoblast and the fetal blood vessel, the basal lamina surrounding ... ... General Embryology: Terminological Dictionary

BARRIER PLACENTAL- a set of structural features of the placenta that prevent (or reduce) the ingress of toxic substances and infection from the mother's blood into the blood of the fetus. See also Placenta… Encyclopedic Dictionary of Psychology and Pedagogy

BARRIER FUNCTION- BARRIER FUNCTION. Barriers are devices that protect the body or its individual organs from environment and thus making it, to a certain extent, independent of the changes taking place in it. There are two kinds... ... Big Medical Encyclopedia

Pharmacotherapy- I Pharmacotherapy (Greek pharmakon medicine + therapeia treatment) treatment of the patient (diseases) medicines. In the traditional sense of F. one of the main methods conservative treatment(Treatment). Modern F. is ... ... Medical Encyclopedia

Today, many mothers know more about pregnancy than our parents did. Therefore, many women during pregnancy worry about the state of their health, and are very worried if the doctor talks about the state of such an important organ during pregnancy as the placenta. This body performs the most important functions, and without it it is impossible to carry a pregnancy in principle.

Deviations in the structure or functioning of the placenta can threaten complications for the mother or fetus, and certain measures must be taken in a timely manner to correct everything. But what can happen to the placenta, and how can it be dangerous? Let's figure it out together.

What is a placenta?

The term "placenta" itself comes from Greek and translated in simple words"cake". Indeed, by appearance the placenta resembles a large and voluminous cake with a “tail” extending from it in the form of an umbilical cord. But this cake has an extremely importance for every woman carrying a baby, it is due to the existence of the placenta that it is possible to endure and give birth normally to a child.

According to the structure of the placenta, or, as it may be called differently in the literature, " children's place", is a complex organ. The beginning of its formation occurs at the time of implantation of the embryo into the wall of the uterus (from the moment the embryo attaches to one of the walls of the uterus).

How is the placenta arranged?

The main part of the placenta are special villi that branch out in it and form from the beginning of pregnancy, resembling the branches of centuries-old trees. Inside the villi, the baby's blood circulates, and outside the villi are actively washed by the blood coming from the mother. That is, the placenta combines two circulatory systems at once - maternal from the side of the uterus, and fetal, from the side amniotic membranes and baby. According to this, the sides of the placenta also differ - smooth, covered with membranes, with an outgoing umbilical cord - from the side of the fetus, and uneven lobed - from the side of the mother.

What is the placental barrier?

It is in the region of the villi that an active and constant exchange of substances takes place between the baby and his mother. Oxygen and all the necessary nutrients for growth and development are supplied from the mother's blood to the fetus, and the baby gives the mother metabolic products and carbon dioxide, which the mother removes from the body for two. And the most important thing is that the blood of the mother and the fetus does not mix in any part of the placenta. The two vascular systems - the fetus and the mother - are separated by a unique membrane that is able to selectively pass some substances and retain others, harmful substances. This membrane is called the placental barrier.

Gradually forming and developing along with the fetus, the placenta begins to fully function by about twelve weeks of pregnancy. The placenta retains bacteria and viruses penetrating into the mother's blood, special maternal antibodies that can be produced in the presence of an Rhesus conflict, but the placenta easily passes necessary for the child nutrients and oxygen. The placental barrier has the property of special selectivity, different substances coming from different parties placental barrier, to varying degrees penetrate the membrane. So, many minerals from the mother actively penetrate to the fetus, but practically do not penetrate from the fetus to the mother. And also, many toxic substances from the baby actively penetrate to the mother, and practically do not pass from her back.

Hormonal function of the placenta

In addition to the excretory function, the implementation of fetal breathing (since the placenta temporarily replaces the baby's lungs), and many other functions, the placenta has another function that is important for pregnancy in general - hormonal. The placenta, with the beginning of its full functioning, can produce up to 15 different hormones that perform various functions during the bearing of the baby. The very first of these are sexual functions, which help in maintaining and prolonging pregnancy. Therefore, gynecologists with the threat of termination of pregnancy in early term always waiting 12-14 weeks, helping in early weeks pregnancy hormones from the outside (duphaston or utrozhestan). Then the placenta begins to work actively and the threat disappears.

The functions of the placenta are so great that in early stages the placenta grows and develops even faster than your baby grows. And this is no accident, the fetus weighs about 5 grams by 12 weeks, and the placenta is up to 30 grams, by the end of pregnancy, at the time of delivery, the size of the placenta will be about 15-18 cm, and its thickness is up to 3 cm, with a weight of about 500 -600 grams.

Umbilical cord

The placenta on the fetal side is connected to the baby by a special strong cord - the umbilical cord, inside which two arteries and one vein pass. The umbilical cord can attach to the placenta in several ways. The first and most common is the central attachment of the umbilical cord, but there may also be a lateral or marginal attachment of the umbilical cord. The function of the umbilical cord does not suffer from the method of attachment. A very rare option for attaching the umbilical cord may be attachment not to the placenta itself, but to its membranes, and this type of attachment is called shell attachment.

Problems with the placenta

Most often, the placenta and umbilical cord system work together and supply the baby with oxygen and nutrition. But sometimes failures can occur in the placenta due to the influence of various factors - external or internal. Happen different kind developmental disorders or problems with the functioning of the placenta. Such changes in the placenta do not go unnoticed for the mother and fetus, often problems with the placenta can be severe consequences. We will talk about the main deviations in the development and functioning of the placenta and how to detect and treat them.

Hypoplasia of the placenta

Reducing the size or thinning of the placenta in medical language is called "placental hypoplasia". This diagnosis should not be frightened, because. it occurs quite often. The fetus is affected only by a significant decrease in the diameter and thickness of the placenta.

Significantly reduced placenta, a small child's place, occurs infrequently. Such a diagnosis is made if the size reduction is significant compared to the lower limit of normal for the size of the placenta in this period pregnancy. The causes of this type of pathology have not yet been clarified, but according to statistics, usually a small placenta is associated with the development of severe genetic abnormalities in the fetus.

I would like to immediately make a reservation that the diagnosis of "placental hypoplasia" is not made according to the data of one ultrasound, it can only be made as a result of long-term observation of the pregnant woman. In addition, it is always worth remembering that there may be individual deviations placenta sizes from standard, generally accepted normal values, which will not be considered a pathology for each specific pregnant woman in each of her pregnancies. So, for a small and slender woman, the placenta should be smaller in size than for a large and tall one. In addition, there is no absolute evidence of the dependence of placental hypoplasia and the presence of genetic disorders in the fetus. But when a diagnosis of "placental hypoplasia" is made, parents will be recommended to undergo medical genetic counseling.

During pregnancy, a secondary decrease in the size of the placenta may occur, which may be associated with the impact of various adverse factors during the bearing of the baby. It can be chronic stress or starvation, drinking alcohol or smoking, drug addiction. Also, the causes of underdevelopment of the placenta during pregnancy can be hypertension in the mother, a sharp exacerbation of chronic pathology, or the development during pregnancy of some acute infections. But in the first places with the underdevelopment of the placenta is preeclampsia with the development severe edema, high blood pressure and the appearance of protein in the urine.

There are changes in the thickness of the placenta. The placenta is considered to be thinned, which has insufficient mass at quite normal sizes for its terms. Often such thin placentas are found in birth defects fetus, and children are born with manifestations that gives serious problems with the health of the newborn. But unlike the initially hypoplastic placenta, such children are not associated with the risks of developing dementia.

Sometimes a membranous placenta is formed - it is very wide and very thin, up to 40 cm in diameter, almost twice as large as normal. Usually the cause of the development of such a problem is a chronic inflammatory process in the endometrium, which leads to dystrophy (exhaustion) of the endometrium.

Hyperplasia of the placenta

In contrast, there is a variant of a very large, giant placenta, which usually occurs in the case of severe course pregnancy diabetes. An increase (hyperplasia) of the placenta is also found in diseases of pregnant women such as toxoplasmosis or syphilis, but this happens infrequently. An increase in the size of the placenta may be the result of kidney pathology in the unborn baby, if present, when the fetal red blood cells with the Rh protein begin to attack the mother's antibodies. The placenta can significantly increase in case of thrombosis of its vessels, if one of the vessels is clogged, as well as in pathological growths small vessels inside the villi.

An increase in the thickness of the placenta more than normal may be due to its premature aging. Thickening of the placenta is also caused by pathologies such as Rhesus conflict, fetal dropsy, diabetes mellitus in pregnancy, preeclampsia, viral or infectious diseases transferred during pregnancy, placental abruption. Thickening of the placenta is normal in multiple pregnancies.

In the first and second trimesters, an increase in the placenta usually indicates a past viral disease (or latent carriage of the virus). In this case, the placenta grows to prevent disease of the fetus.

The rapid growth of the placenta leads to its premature ripening and hence aging. The structure of the placenta becomes lobulated, calcifications form on its surface, and the placenta gradually ceases to provide the fetus necessary quantity oxygen and nutrients. The hormonal function of the placenta also suffers, which leads to premature birth.

Treatment of placental hyperplasia usually consists of careful monitoring of the fetus.

What is the danger of changing the size of the placenta?

Why are doctors so worried about a significant change in the size of the placenta? Usually, in the case of a change in the size of the placenta, functional insufficiency in the work of the placenta can also develop, that is, the so-called feto-placental insufficiency (FPN), problems with the supply of oxygen and nutrition to the fetus, will form. The presence of FPI may mean that the placenta cannot fully cope with the tasks assigned to it, and the child experiences a chronic lack of oxygen and nutrient supply for growth. However, problems may increase snowball, the child's body will suffer from a lack of nutrients, as a result, it will begin to lag behind in development and IUGR will form (delay prenatal development in the fetus) or fetal growth retardation syndrome (FGR).

To prevent this from happening, it is best to engage in prevention in advance. similar states, treatment of chronic pathology even before the onset of pregnancy, so that exacerbations do not occur during gestation. During pregnancy, it is important to control arterial pressure, blood glucose levels and to protect the pregnant woman as much as possible from any infectious diseases. It is also necessary good nutrition with enough proteins and vitamins.

When making a diagnosis of "placental hypoplasia" or "placental hyperplasia", it is required first of all careful observation over the course of pregnancy and the condition of the fetus. It is impossible to cure or fix the placenta, but there are a number of drugs prescribed by a doctor to help the placenta carry out its functions.

In the treatment of developing feto-placental insufficiency, special preparations- trental, actovegin or chimes, which are able to improve blood circulation in the placental system both from the mother and the fetus. In addition to these drugs, intravenous infusions of drugs can be prescribed - rheopolyglucin with glucose and ascorbic acid, saline solutions. The development of FPI can have varying degrees of severity and with it you cannot self-medicate, this can lead to the loss of a child. Therefore, it is necessary to comply with all the appointments of an obstetrician-gynecologist.

Changes in the structure of the placenta

The normal placenta has a lobular structure, it is divided into approximately 15-20 lobules of equal size and volume. Each of the lobules is formed from villi and a special tissue that is between them, and the lobules themselves are separated from each other by partitions, however, not complete. If changes occur in the formation of the placenta, new variants of the structure of the lobules may occur. So, the placenta can be bilobed, consisting of two equal parts, which are interconnected by a special placental tissue, a double or triple placenta can also be formed, the umbilical cord will be attached to one of the parts. Also, a small additional lobule can be formed in a normal placenta. Even less often, the so-called "fenestrated" placenta can occur, which has areas covered with a shell and resembling windows.

There can be many reasons for such deviations in the structure of the placenta. Most often, this is a genetically incorporated structure, or a consequence of problems with the uterine mucosa. Prevention of such problems with the placenta can be an active treatment of inflammatory processes in the uterine cavity even before pregnancy, during the planning period. Although deviations in the structure of the placenta do not affect the child so much during pregnancy, and almost never affect its development. But in childbirth, such a placenta can cause a lot of trouble for doctors - such a placenta can be very difficult to separate from the uterine wall after the birth of the baby. In some cases, separation of the placenta requires manual control of the uterus under anesthesia. Treatment of the abnormal structure of the placenta during pregnancy is not required, but in childbirth it is necessary to remind the doctor about this so that all parts of the placenta are born and there are no pieces of the placenta left in the uterus. It is dangerous by bleeding and infection.

The degree of maturity of the placenta

The placenta in the course of its existence goes through four successive stages of maturation:

The degree of maturity of the placenta 0- normally lasts up to 27-30 weeks. Sometimes at these stages of pregnancy, 1 degree of placental maturity is noted, which can be caused by smoking or drinking alcohol during pregnancy, as well as a previous infection.

Degree of maturity of the placenta 1- from 30 to 34 weeks of pregnancy. During this period, the placenta stops growing, its tissues thicken. This is a crucial period when any deviations can pose a danger to the health of the fetus.

Degree of maturity of the placenta 2- lasts from 34 to 39 weeks of pregnancy. This stable period when some advance of placental maturity should not cause concern.

Degree of maturity of the placenta 3- normally can be diagnosed starting from the 37th week of pregnancy. This is the stage natural aging placenta, but if it is combined with fetal hypoxia, the doctor may recommend a caesarean section.

Disorders in the maturation of the placenta

For each stage of placenta formation, there are normal timing in weeks of pregnancy. Too fast or slow passage of certain stages by the placenta is a deviation. The process of premature (accelerated) maturation of the placenta is uniform and uneven. Usually expectant mothers with a weight deficit face uniform premature aging of the placenta. Therefore, it is important to remember that pregnancy is not a time for compliance. different diets, since their consequences can be premature birth and the birth of a weak baby. The placenta will ripen unevenly if there are problems with blood circulation in some of its areas. These complications usually occur in women with overweight, with prolonged late toxicosis of pregnancy. Uneven maturation of the placenta often occurs with repeated pregnancies.

Treatment, as with feto-placental insufficiency, is aimed at improving blood circulation and metabolism in the placenta. To prevent premature aging of the placenta, it is necessary to take measures to prevent pathologies and gestosis.

But delays in the maturation of the placenta occur much less frequently, and the most common reasons for this may be the presence diabetes in pregnant women, drinking alcohol and smoking. Therefore, it is worth giving up bad habits during childbearing.

placental calcifications

The normal placenta has a spongy structure, but by the end of pregnancy, some of its areas may become stony, such areas are called petrificates or placental calcifications. Hardened parts of the placenta are not able to perform their functions, but usually the remaining parts of the placenta do an excellent job with the task assigned to them. Typically, calcification occurs when premature aging placenta or post-pregnancy. In such cases, the doctor will closely monitor the pregnant woman in order to exclude the development of fetal hypoxia. But usually such a placenta functions quite normally.

Low insertion and placenta previa

Ideally, the placenta should be located at the top of the uterus. But there are a number of factors that prevent the normal location of the placenta in the uterine cavity. These can be uterine fibroids, tumors of the uterine wall, malformations of its development, many pregnancies in the past, inflammatory processes in the uterus or abortion.

Requires closer observation. Usually during pregnancy, it tends to rise. In this case, there will be no obstacles for natural childbirth. But it happens that the edge of the placenta, part of it or the entire placenta overlaps internal os uterus. With partial or complete overlapping of the uterine os by the placenta natural childbirth impossible. Usually, with an abnormal location of the placenta, a caesarean section is performed. Such wrong positions placentas are called incomplete and complete placenta previa.

During pregnancy, a woman may experience bleeding from the genital tract, which leads to anemia, fetal hypoxia. The most dangerous partial or complete detachment placenta, which leads to the death of the fetus and a threat to the life of the mother. , including sexual, you can not engage exercise, swim in the pool, walk a lot and work.

What is placental abruption?

What is premature detachment placenta? This is a condition when the placenta (normally or abnormally located) leaves the place of its attachment earlier than its due date, that is. With placental abruption, an emergency caesarean section is necessary to save the life of the mother and fetus. If the placenta exfoliated in small areas, then doctors try to stop this process, keeping the pregnancy. But even with minor placental abruption and slight bleeding, the risk of repeated episodes of abruption remains until childbirth, and the woman is carefully monitored.

Placental abruption can be caused by trauma or blows to the abdomen, the presence of chronic pathologies in a woman, which leads to problems with blood circulation, defects in the formation of the placenta. Premature placental abruption can be caused by complications during pregnancy - most often gestosis with increased pressure, protein in the urine and edema, in which all organs and systems of the mother and fetus suffer. It is important to remember that placental abruption is most dangerous complication pregnancy!

Placental abruption
Rice. 1 - full presentation placenta;
Rice. 2- marginal presentation placenta;
Rice. 3 - partial placenta previa
1 - cervical canal; 2 - placenta; 3 - umbilical cord; 4 - fetal bladder

Dense attachment and accreta of the placenta

Sometimes there are anomalies not only in the place, but also in the way the placenta is attached to the wall of the uterus. A very dangerous and serious pathology is placenta accreta, in which placental villi are attached not only to the endometrium (the inner layer of the uterus, which exfoliates during childbirth), but also grow deep into the tissues of the uterus, into its muscular layer.

There are three degrees of severity of placental accreta, depending on the depth of germination of the villi. In the most severe, third degree, the villi grow through the entire thickness of the uterus and can even lead to uterine rupture. The cause of placenta accreta is the inferiority of the endometrium due to birth defects uterus or acquired problems.

The main risk factors for placenta accreta are frequent abortions, caesarean sections, fibroids, as well as intrauterine infections, malformations of the uterus. A certain role can be played by low placentation, since in the region of the lower segments, the germination of villi into the deeper layers of the uterus is more likely.

With true placenta accreta, in the vast majority of cases, removal of the uterus with placenta accreta is required.

An easier case is a dense attachment of the placenta, which differs from the increment in the depth of penetration of the villi. Dense attachment occurs with a low location of the placenta or its presentation. The main difficulty with such an attachment of the placenta is a delay in its birth or the complete impossibility of independent discharge of the placenta in the third stage of labor. With tight attachment, they resort to manual separation of the placenta under anesthesia.

Diseases of the placenta

The placenta, like any organ, can get sick. It can become infected, infarcts (areas deprived of blood circulation) can develop in it, blood clots can form inside the vessels of the placenta, and the placenta itself can even undergo tumor degeneration. But this, fortunately, happens infrequently.

Infectious lesions of the tissues of the placenta (placentitis), caused by various microbes that can penetrate the placenta different ways. So, they can be brought in with the blood stream, penetrate from fallopian tubes ascending from the vagina, or from the uterine cavity. The process of inflammation can be extended to the entire thickness of the placenta or occur in its individual sections. In this case, the treatment should be specific, and it depends on the type of pathogen. Of all the possible drugs, the one that is acceptable for pregnant women at a given time will be selected. And for the purpose of prevention before pregnancy, it is necessary to carry out a full-fledged therapy of chronic infections, especially in the genital tract.

Placental infarction usually develops, like any other, as a result of prolonged ischemia (vasospasm of the placenta), and then the parts of the placenta that receive blood from these vessels die as a result of oxygen deficiency. Usually, heart attacks in the placenta occur as a result of a severe course of preeclampsia or with the development of hypertension in a pregnant woman. Placentitis and placental infarction can cause FPI and problems with fetal development.

Sometimes, as a result of inflammation or damage to the vascular wall, with a violation of blood viscosity, or with sudden movements of the fetus, blood clots form inside the placenta. But small blood clots do not affect the course of pregnancy.

The placenta connects the fetus with the mother's body and consists of the fetal (villous chorion) and maternal (decidua) parts (Fig. 20-4 and 20-5). In the placenta, the chorionic villi containing the blood capillaries of the fetus are washed by the blood of the pregnant woman circulating in the intervillous space. The blood of the fetus and the blood of the pregnant woman are separated by the placental barrier - the trophoblast, the stroma of the villi and the endothelium of the fetal capillaries. The transfer of substances across the placental barrier is carried out by passive diffusion (oxygen, carbon dioxide, electrolytes, monosaccharides), active transport (iron, vitamin C) or facilitated diffusion mediated by carriers (glucose, Ig).

Rice. 20–5 . Decidual shell uterus And placenta. The uterine cavity is lined by the parietal part of the decidua. The decidua facing the villous chorion is part of the placenta.

Blood flow in the placenta

Umbilical cord, or umbilical cord (Fig. 20-3, 20-4) - a cord-like formation containing two umbilical arteries and one umbilical vein that carry blood from the fetus to the placenta and back. The umbilical arteries carry venous blood from the fetus to the chorionic villi in the placenta. Through the vein, arterial blood flows to the fetus, enriched with oxygen in the blood capillaries of the villi. The total volumetric blood flow through the umbilical cord is 125 ml/kg/min (500 ml/min).

Arterial blood pregnant it is injected directly into the intervillous space (lacunae, see Fig. 20-3 and 20-4) under pressure and shocks from about a hundred spiral arteries located perpendicular to the placenta. The lacunae of a fully formed placenta contain about 150 ml of washing villi of maternal blood, completely replaced 3-4 times per minute. From the intervillous space, venous blood flows through venous vessels located parallel to the placenta.

Placental barrier. The placental barrier (maternal blood  fetal blood) includes: syncytiotrophoblast  cytotrophoblast  trophoblast basement membrane  connective tissue of the villus  basement membrane in the wall of the villus capillaries  endothelium of the villus capillaries. It is through these structures that the exchange between the blood of the pregnant woman and the blood of the fetus takes place. It is these structures that implement the protective (including immune) function of the fetus.

Functions of the placenta

The placenta performs many functions, including the transport of nutrients and oxygen from the pregnant woman to the fetus, the removal of fetal waste products, the synthesis of proteins and hormones, and the immunological protection of the fetus.

Transport function

 Transfer oxygen And dioxide carbon occurs by passive diffusion.

 O 2 . The partial pressure of oxygen (Po 2 ) of the arterial blood of the spiral arterioles at pH 7.4 is 100 mm Hg with an oxygen saturation of Hb of 97.5%. At the same time, Po 2 blood in the venous part of the fetal capillaries is 23 mm Hg. at 60% saturation of Hb with oxygen. Although the Po 2 of maternal blood rapidly decreases to 30–35 mm Hg as a result of oxygen diffusion, even this difference of 10 mm Hg enough to provide an adequate supply of oxygen to the fetus. Efficient diffusion of oxygen from mother to fetus is facilitated by additional factors.

 The fetal Hb has a greater affinity for oxygen than the definitive Hb of the pregnant woman (the HbF dissociation curve is shifted to the left). At the same Po2, fetal Hb binds 20–50% more oxygen than maternal Hb.

 The concentration of Hb in the blood of the fetus is higher (this increases the oxygen capacity) than in the blood of the mother. Thus, despite the fact that fetal oxygen saturation rarely exceeds 80%, fetal tissue hypoxia does not occur.

The pH of fetal blood is lower than the pH of adult whole blood. With an increase in the concentration of hydrogen ions, the affinity of oxygen for Hb decreases (the effect Bor a), so oxygen is more easily transferred from the mother's blood to the tissues of the fetus.

 CO 2 diffuses through the structures of the placental barrier in the direction of the concentration gradient (approximately 5 mm Hg) between the blood of the umbilical arteries (48 mm Hg) and the blood of lacunae (43 mm Hg). In addition, fetal Hb has a lower affinity for CO 2 than maternal definitive Hb.

 Urea, creatinine, steroid hormones, fatty acids, bilirubin. Their transfer occurs by simple diffusion, but the placenta is poorly permeable to bilirubin glucuronides formed in the liver.

 Glucose- facilitated diffusion.

 Amino acids And vitamins- active transport.

 Squirrels(e.g. transferrin, hormones, some Ig classes), peptides, lipoproteins receptor-mediated endocytosis.

 electrolytes- Na + , K + , Cl - , Ca 2+ , phosphate - cross the barrier by diffusion and active transport.

Immunological protection

 Maternal antibodies of the IgG class transported through the placental barrier provide passive immunity to the fetus.

 The body of a pregnant woman does not reject an immunologically alien fetus due to local inhibition of the woman's cellular immunity reactions and the absence of glycoproteins of the major histocompatibility complex (HLA) in chorion cells.

 Chorion synthesizes substances that inhibit the cellular immune response (an extract from syncytiotrophoblast inhibits in vitro reproduction of cells of the immune system of the pregnant woman).

 Trophoblast cells do not express HLA Ag, which provides protection of the fetoplacental complex from recognition by immunocompetent cells of the pregnant woman. That is why the areas of trophoblast split off from the placenta, getting into the lungs of a woman, are not rejected. At the same time, other types of cells in the villi of the placenta carry HLA Ag on their surface. The trophoblast also does not contain erythrocyte Ag systems AB0 and Rh.

Detoxification some LS.

Endocrine function. The placenta is an endocrine organ. The placenta synthesizes many hormones and other biologically active substances that are important for normal flow pregnancy and fetal development (CHT, progesterone, human chorionic somatomammotropin, fibroblast growth factor, transferrin, prolactin, relaxins, corticoliberin, estrogens and others; see Fig. 20-6, as well as Fig. 20-12 in the book, see also table .18–10).

 chorionic gonadotropin(CHT) maintains the continuous secretion of progesterone in the corpus luteum until the placenta begins to synthesize progesterone in an amount sufficient for the normal course of pregnancy. HCG activity increases rapidly, doubling every 2-3 days and reaching a peak on the 80th day (80,000-100,000 IU / L), then decreases to 10,000-20,000 IU / L and remains at this level until the end of pregnancy.

 Marker pregnancy. HCG is produced only by syncytiotrophoblast cells. HCG can be detected in the blood serum of a pregnant woman 8-9 days after fertilization. The amount of secreted HCG is directly related to the mass of the cytotrophoblast. In early pregnancy, this circumstance is used to diagnose normal and abnormal pregnancy. The content of HCG in the blood and urine of a pregnant woman can be determined by biological, immunological and radiological methods. Immunological (including radioimmunological) tests are more specific and sensitive than biological methods. With a decrease in the concentration of HCG by half compared to normal values, implantation disorders (for example, an ectopic pregnancy or an undeveloped uterine pregnancy) can be expected. An increase in the concentration of HCG above normal values is often associated with multiple pregnancies or hydatidiform mole.

 Stimulation secretions progesterone yellow body. An important role of HCG is to prevent the regression of the corpus luteum, which usually occurs 12-14 days after ovulation. Significant structural homology between HCG and LH allows HCG to bind to luteocyte receptors for LH. This leads to the continuation of the work of the corpus luteum after the 14th day from the moment of ovulation, which ensures the progression of pregnancy. Starting from the 9th week, the synthesis of progesterone is carried out by the placenta, the mass of which by this time allows the formation of progesterone in an amount sufficient to prolong the pregnancy (Fig. 20–6).

 Stimulation synthesis testosterone cells Leidiga in a male fetus. By the end of the first trimester, HCG stimulates the fetal gonads to synthesize steroid hormones necessary for the differentiation of the internal and external genital organs.

 Synthesis and secretion of HCG maintains secreted cytotrophoblast gonadoliberin.

 Progesterone. In the first 6-8 weeks of pregnancy, the main source of progesterone is the corpus luteum (the content in the blood of a pregnant woman is 60 nmol / l). Starting from the second trimester of pregnancy, the placenta becomes the main source of progesterone (blood content 150 nmol / l). corpus luteum continues to synthesize progesterone, but in the last trimester of pregnancy, the placenta produces it 30-40 times more. The concentration of progesterone in the blood continues to increase until the end of pregnancy (blood content 500 nmol / l, about 10 times more than outside pregnancy), when the placenta synthesizes 250 mg of progesterone per day. To determine the content of progesterone, a radioimmune method is used, as well as the level of pregnandiol, a metabolite of progesterone, chromatographically.

 Progesterone promotes decidualization of the endometrium.

 Progesterone, inhibiting the synthesis of Pg and reducing sensitivity to oxytocin, inhibits the excitability of the myometrium before the onset of childbirth.

 Progesterone promotes the development of breast alveoli.

Rice. 20 –6 . Content hormones V plasma blood at pregnancy

 Estrogens. During pregnancy, the content of estrogens in the blood of a pregnant woman (estrone, estradiol, estriol) is significantly increased (Fig. 20-6) and exceeds the values outside of pregnancy by about 30 times. Wherein estriol makes up 90% of all estrogens (1.3 nmol/l at the 7th week of pregnancy, 70 nmol/l by the end of pregnancy). By the end of pregnancy, urinary excretion of estriol reaches 25–30 mg/day. The synthesis of estriol occurs during the integration of the metabolic processes of the pregnant woman, placenta and fetus. Most of the estrogen is secreted by the placenta, but it does not synthesize these hormones. de novo, but only the aromatization of steroid hormones synthesized by the adrenal glands of the fetus. Estriol is an indicator of the normal functioning of the fetus and the normal functioning of the placenta. For diagnostic purposes, the content of estriol is determined in peripheral blood and daily urine. High concentrations of estrogen cause an increase in the muscle mass of the uterus, the size of the mammary gland, and the external genital organs.

 Relaxins- hormones from the insulin family - during pregnancy, they have a relaxing effect on the myometrium, before childbirth they lead to the expansion of the uterine os and an increase in the elasticity of the tissues of the pubic joint.

 Somatomammotropins 1 And 2 (placental lactogens) are formed in the placenta 3 weeks after fertilization and can be determined in the blood serum of a woman by radioimmunoassay from 6 weeks of pregnancy (35 ng/ml, 10,000 ng/ml at the end of pregnancy). The effects of somatomammotropins, like those of growth hormone, are mediated by somatomedins.

 Lipolysis. Stimulate lipolysis and increase plasma free fatty acids (energy reserve).

 carbohydrate exchange. Suppress glucose utilization and gluconeogenesis in pregnant women.

 insulinogenic action. They increase the content of insulin in the blood plasma, while reducing its effects on target cells.

 Dairy glands. They induce (like prolactin) the differentiation of secretory sections.

 Prolactin. During pregnancy, there are three potential sources of prolactin: the anterior pituitary of the mother and fetus, and the decidua of the uterus. In a non-pregnant woman, the content of prolactin in the blood is in the range of 8-25 ng / ml, during pregnancy it gradually increases to 100 ng / ml by the end of pregnancy. The main function of prolactin is to prepare the mammary glands for lactation.

 Releasing–hormones. In the placenta, all known hypothalamic releasing hormones and somatostatin are synthesized (see Tables 18–10).

The human placenta is made up of maternal and fetal tissues. Blood vessels mothers fall into the intervillous space, into which outgrowths of the chorion penetrate. In the latter, in loose tissue, there are vessels of the fetus.

On the surface washed by the mother's blood, there is a syncytial tissue, the so-called trophoblastic membrane. The exchange of matter between the blood of the mother and the fetus is thus carried out through the following structures: the trophoblastic membrane, the loose tissue of the stroma of the outgrowths of the chorion, the endothelium of the capillaries of the chorion. During the development of the fetus, the thickness of these layers is not the same and at the end of the gestation period is only a few microns. The area of contact between the surface of the choroid outgrowths and the mother's blood is also not constant and in the prenatal period is about 14 m 2. IN early periods pregnancy, the barrier thickness is significantly greater, and the surface area is less. In this regard, the permeability of the placental barrier for xenobiotics at different periods of gestation is not the same. In general, in humans, it constantly increases until the 8th month of pregnancy, and then decreases again. The consequences for the fetus of the penetration of xenobiotics through the placenta are determined by the ratio of the power of the toxicant flow through the placental barrier on the one hand, the size developing fetus and the state of dividing and differentiating cells of its tissues, on the other.

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