The placental barrier consists of. Placenta, types of placentas, placental barrier. Blood flow in the placenta

PLACENTAL BARRIER

placental barrier, a histohematic barrier that regulates the penetration of various substances from the mother’s blood into the fetal blood and back. 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 internal environment of the mother from the penetration of substances from the fetal blood that disturb it. P. b. consists of trophoblast epithelium, syncytium covering the chorionic villi of the placenta, connective tissue of the villi and the endothelium of their capillaries. In the terminal villi, many capillaries are located immediately 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 is also data on the passage through P. b. high-molecular substances, antibodies, antigens, as well as viruses, bacteria, helminths. The penetration of high-molecular substances, antigens, bacteria is observed in the pathology of pregnancy, since the function P. b. is violated. P. b. is selectively permeable to substances with a molecular weight below 350. Thus, through P. b. Acetylcholine, histamine, and adrenaline cannot penetrate. Function P. b. this is done with the help of special enzymes that destroy these substances. During pregnancy pathology, many medicinal substances, as well as products of impaired metabolism, penetrate into the blood of the fetus and have a damaging effect on it. See also .

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

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Placental barrier

Placental barrier - a set of morphological and functional features of the placenta that determine its ability to selectively pass substances from the mother’s blood to the fetus and in the opposite direction. Functions of 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 internal environment of the mother from the penetration of substances from the fetal blood that disrupt its homeostasis. P. b. consists of trophoblast epithelium, syncytium covering the chorionic villi of the placenta, connect. tissue of the villi and the endothelium of their capillaries. In the terminal villi there are many. capillaries are located immediately under the syncytium, and P. b. at the same time they consist of 2 unicellular membranes. It has been established that substances that say can mainly enter the blood of the fetus from the mother’s body. m below 350. There is also data on the passage through P. b. high-molecular substances, antibodies, antigens, as well as viruses, bacteria, helminths. The penetration of high-molecular substances, antigens, and bacteria is observed in the pathology of pregnancy, since the function of P. b. is violated. P. b. is selectively permeable in relation to substances with a mol. m below 350. Thus, acetylcholine, histamine, and adrenaline cannot penetrate through P. 6. Function P. b. this is done with the help of special enzymes that destroy these substances. In case of pregnancy pathology, plural. medicines. substances, as well as products of impaired metabolism, penetrate into the blood of the fetus and have a damaging effect on it.

The placental barrier refers to the selective properties of the placenta, as a result of which some substances penetrate from the mother’s blood into the blood of the fetus, while others are retained or enter the fetal body after appropriate biochemical processing.

The barrier separating the blood of the mother and the fetus in the intervillous space consists of the trophoblast epithelium, or syncytium, covering the villi, the connective tissue of the villi and the endothelium of their capillaries.

The barrier function of the placenta can only be performed under physiological conditions. The permeability of the placental barrier to harmful substances and microbes increases with pathological changes in the placenta resulting from damage to the villi by microbes and their toxins. Placental permeability may also increase due to thinning of the syncytium with increasing gestational age.

The exchange of gases (oxygen, etc.), as well as true solutions through the placental membrane, occurs according to the laws of osmosis and diffusion. This is facilitated by the difference in partial pressure in the blood of the mother and fetus. Proteins, fats, carbohydrates and other substances penetrate the placental barrier in the form of simple compounds formed under the influence of the enzymatic function of the placenta.

Different concentrations of potassium, sodium, phosphorus and other substances are created in the blood of the mother and fetus. Mother's blood, compared to fetal blood, is richer in proteins, neutral fats and glucose.

The fetal blood contains more protein-free nitrogen, free amino acids, potassium, calcium, inorganic phosphorus and other substances.

The placental barrier only partially protects the fetus from the penetration of harmful substances. Drugs, alcohol, nicotine, potassium cyanide, sulfonamides, quinine, mercury, arsenic, potassium iodide, antibiotics (penicillin and streptomycin), vitamins and hormones can pass through the placenta.

The penetration of substances from maternal blood into fetal blood is greatly influenced by the size of the molecules. During physiological pregnancy, substances with a molecular weight below 350 can penetrate through the placental barrier into the blood of the fetus. In pathologies of pregnancy (toxicosis, ionizing radiation, etc.), as a result of dysfunction of the placental barrier, high-molecular substances (antigens, antibodies, viruses) can penetrate into the blood of the fetus , toxins, bacteria, protozoa and helminths).

Immune system of the placenta. Barrier function of the placenta.

Immune system of the placenta.

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

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

Barrier function of the placenta.

Concept " placental barrier"includes the following histological formations: syncytiotrophoblast, cytotrophoblast, a layer of mesenchymal cells (villous stroma) and the endothelium of the fetal 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, in contrast from the blood-brain barrier, the selective permeability of which is characterized by the passage of various substances in only one direction (blood - cerebrospinal fluid), placental barrier regulates the transition 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 enter it accidentally obeys 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, microelements, 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 enter the maternal body (chemical production agents, medications, etc.), the barrier functions of the placenta are expressed to a much lesser extent.

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

Limited barrier functions placenta in relation to chemical substances that accidentally enter the mother’s body are manifested in the fact that toxic chemical products, most medications, nicotine, alcohol, pesticides, infectious agents, etc. pass through the placenta relatively easily. This poses a real risk of adverse effects of these agents on the embryo and fetus.

Barrier functions of the placenta are most fully manifested only in physiological conditions, i.e. during 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 to substances that, under normal physiological conditions, pass through it in limited quantities.

Today, the term “placenta” no longer surprises 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 is incomprehensible here? The child's place has the properties to protect the developing embryo from harmful influences and toxic substances. In fact, this organ is a real mystery and miracle of nature.

Under protection

The placental barrier 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 immunological conflict. The first trimester of pregnancy is the most difficult. Partly because the placenta has not yet formed, which means that the embryo’s body is completely unprotected. From about 12 weeks she becomes fully involved in her work. From now on, she is ready to perform all her functions.

How does the placenta work?

This is an important point, without which we cannot continue our conversation. The word “placenta” itself comes to us from Latin. It translates as “flatbread”. Its main part is special villi, which begin to form from the first days of pregnancy. Every day they become more and more ramified. At the same time, the child’s blood is inside them. At the same time, maternal blood enriched with nutrients enters from the outside. That is, the placental barrier primarily has a separation function. This is very important, since this organ regulates the metabolism between two closed systems. According to this statement, the outer and inner sides of the placenta have a different structure. It is smooth inside. The outer side is 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 ensure the exchange of substances between the woman and the embryo. The mother's blood brings oxygen to the baby and the fetus gives carbon dioxide to the pregnant girl. so far they have one between them. And this is where the greatest mystery lies. The placental barrier separates the blood of mother and fetus so well that they do not mix.

At first glance it seems unimaginable, but the two vascular systems are separated by a unique membrane septum. She selectively misses what is important for the development of the fetus. On the other hand, toxic, harmful and dangerous substances are retained here. Therefore, doctors say that starting from the 12th week, the expectant mother can already relax a little. The placenta is able to protect the child’s body from many unfavorable factors.

Only the most important

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

It should be noted that the septum is highly selective. The same substances that cross the placental barrier reach the mother and fetus in different ways. For example, fluoride penetrates very easily and quickly from a woman to a baby, but is not allowed back at all. The situation is similar with bromine.

What is the regulation of metabolism?

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

First of all, we are interested in how the supply of vital nutrients is regulated. Everything is quite simple here. Lipids and carbohydrates, proteins and vitamins are constantly available 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 talk about toxic substances that enter the body of a pregnant woman. The placental barrier separates lymph and blood. This means that those toxins that pass through the mother’s bloodstream will not reach the fetus in their pure form. However, after passing through natural filters (liver and kidneys) in 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 have the ability to overcome the placental barrier.

Limited barrier functions

Nature could not have foreseen the development of modern industry. Therefore, chemical products pass through the natural barrier relatively easily. 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 the particular substance. We will note only a few points, in fact there are many more. Thus, drugs with a molecular weight (less than 600 g/mol) cross the placental barrier much faster. At the same time, those that have a lower indicator practically do not penetrate. For example, these are insulin and heparin, which can be prescribed without fear during pregnancy.

There is one more sign. Fat-soluble substances penetrate the placenta much better than water-soluble substances. Therefore, hydrophilic compounds are more desirable. In addition, doctors know that the likelihood of a substance penetrating the placenta depends on the time the drug remains in the blood. All long-acting drugs are more dangerous than those that are metabolized quickly.