The birth of a child is a long-awaited event in the life of a family. Pregnancy of a woman is a crucial period of her life, when the health of her future baby is laid. Many factors influence its intrauterine development, but the most important one is the normal functioning of the mother-placenta-child system. The placenta in this chain is a key link. A lot depends on its area, location and formation of structural units - placental cotyledons. Violations in its formation threaten the health and even the life of the mother and child. This article is about what cotyledon is, the structure of the placenta and the formation of the connection between the fetus and the mother in the prenatal period of its development.
Baby place
From the beginning of zygote implantation, the mother-fetus system has been functioning in the uterus. And the main component of this system is the placenta (from the Latin placenta - flat cake, fritters). This is a temporary complex organ that is formed by derivatives of the embryoblast and trophoblast (zygote membranes). First of all, the functions of the placenta provide the conditions for the physiological course of pregnancy and the normal development of the embryo. All metabolic, hormonal and immune processes are provided by the vascular system of the mother, which is closely intertwined in the structural components of the placenta - cotyledon. It is here that the metabolism is ensured and the placental barrier is created.
In the normal course of pregnancy up to 16 weeks, placental growth is faster than fetal growth. In the case of the death of the embryo, the growth of the placenta is inhibited, dystrophic phenomena begin to progress, which leads to the termination of pregnancy. Having reached full maturity by 38 weeks of pregnancy, the placenta stops the growth of blood vessels, which also leads to the onset of labor, termination of pregnancy and rejection of the placenta.
The structure of the placenta
The layers of the placenta are formed by two plates - the chorial and basal, and between them are the villi of the fetal chorion and the intervillous space. The maternal side of the placenta, which is adjacent to the walls of the uterus, has a rough surface and is formed by the decidual membrane.
The placenta side facing the fetus is called the fetal and is divided into autonomous segments. These placenta lobes are called cotyledons. Cotyledon lacunae are filled with maternal blood, the volume of which is about 150 ml. Blood is exchanged every 3 minutes. This part is represented by numerous villi of the chorion (fetal membrane), which are combined into structural and functional units of the placenta - cotyledon. The total surface of the villi in one cotyledon is about 15 square meters.
A mature placenta is a disc-shaped structure with a diameter of up to 20 centimeters and a mass of up to 600 grams. The thickness of the placenta is normal up to 3.5 centimeters.
How does it all begin
Placental cotyledons are formed in the following sequence. When the embryo enters the uterus on days 6-7, its shells form a trophoplast, the function of which is to gain a foothold in the uterine mucosa and suppress the immune response of its rejection.
The implantation of the embryo is accompanied by the proliferation of primary villi, which branch and form the villous membrane of the embryo, the chorion.
At 3-4 weeks of pregnancy, the blood vessels of the fetus germinate into the secondary villi, which destroy the capillaries in the uterine wall. In the place of their destruction, blood lakes are formed - the primary fossa, which subsequently become the gaps of the placenta cotyledons.
A place where everything happens
The fetal part of the placenta is penetrated by blood vessels that go from the umbilical cord of the fetus. They branch out many times and reach the chorionic villi, which are combined into structurally functional units of the placenta - cotyledon. They are formed by one stem villus, which branches into 2-order villi. The central part of cotyledon (cotyledon) is formed by a cavity in which maternal blood is located and which is surrounded by many villi. The villi of the 2nd order also branch and form villi of the 3rd order. The structure of the placenta cotyledon is comparable to a tree, where the supporting villi is its trunk and the terminal villi are leaves. And the whole tree is immersed in a lacunae with maternal blood.
Cotyledons are separated from each other by septa - basal plate partitions. In the placenta, the total number of cotyledons ranges from 30-50.
Placental barrier
The exchange of blood gases, all nutrients, antibodies and hormones, metabolic products between maternal and fetal blood occurs in the cotyledon of the placenta at the moment of contact of its villi with the blood of the mother. The placental barrier is formed by the external epithelial layer of the villi and the wall of the blood capillary. The latter is located inside the villi of the cotyledon placenta. The structure of this barrier provides selective permeability in both directions.
Due to the permeability of this barrier, the transition of gases and nutrients to the fetus is easily carried out, and metabolic products are removed. But some drugs, nicotine, alcohol, drugs, pesticides easily overcome this barrier. And a whole series of pathogens of infections that have a negative effect on both the fetus and the placenta itself.
Cotyledon functions
In addition to providing the hematoplacental barrier, these structural formations provide the following functions of the placenta:
- Gas exchange. Oxygen enters the bloodstream of the fetus, and carbon dioxide is transported in the opposite direction due to the simple laws of diffusion.
- Nutrition and excretion. Water, electrolytes, vitamins, nutrients and minerals from the mother’s blood diffuse into the fetal blood. In the opposite direction there is a transportation of metabolic products - urea, creatinine.
- Regulation. The placenta secretes many hormones that regulate the course of pregnancy. For example, chorionic gonadotropin, progesterone, placental lactogen, prolactin. As well as testosterones, serotonin, relaxin.
- Protection. The immune properties of the placenta are the passage of antibodies from the blood of the mother into the fetal blood. This is how primary innate immunity is formed.
Norm and pathology
Normally, the placenta is located in the anterior or posterior wall of the uterus. Its location is easily determined by ultrasound and serves as the basis for diagnosis for the course of pregnancy and its timing. The thickness of the child's place grows up to 36-37 weeks, reaching sizes up to 4 centimeters, and then its growth stops, which is considered a mature placenta.
But sometimes the placenta is located in other places of the uterus:
- Low location. In this case, the placenta is located close to the uterine pharynx. In most women, this situation is aligned to a later date. Only in 5% of pregnant women the location remains low by 32 weeks. This situation is dangerous premature detachment of the placenta, and doctors decide on the method of delivery.
- Placenta previa is the position of the organ when it completely blocks the internal pharynx of the uterus. These conditions are fraught with uterine bleeding and termination of pregnancy.
Other pathologies of the child's place
- Full attachment of the placenta. This is a condition when placental villi not only grow to the endometrium of the uterus, but also penetrate the uterine muscle layer - the myometrium. It is safe for the fetus, but during delivery, the placenta doctors have to tear away the placenta manually.
- Placental abruption is a partial or complete detachment of the placenta. It is considered a severe pregnancy pathology, and patients are subject to urgent hospitalization. It occurs in 1-3 pregnant women out of a thousand.
Thin or thick
The insufficiency of the function of the placenta can occur with its early maturation in a decrease or increase in its thickness.
A “thin” placenta (hypoplasia) - up to 20 mm in the third trimester - is fraught with the threat of abortion, fetal malnutrition (developmental delay). The same consequences occur with a "thick" placenta (more than 5 centimeters).
In addition, there is a pathology associated with a decrease in the placenta area with its normal thickness. This can be the cause of genetic pathologies that often accompany fetal malformations (Down syndrome). In this case, a small child's place cannot cope with providing the fetus with all the nutrients and oxygen, which leads to its developmental lag.
Too large a placenta is also not good. Its growth, as a rule, is often associated with various infections transmitted by a pregnant woman. overgrowth of the placenta is often the case with the Rh conflict of the mother and fetus. In this case, cotyledons degenerate and age. And again we have placental insufficiency and premature aging of the placenta (extinction of its functions and growth).
Sometimes pathology manifests itself in the form of an additional cotyledon placenta. In this case, the lobule of the child's place is located separately and may remain in the uterus during childbirth. That is why, after the placenta is released in labor, it is carefully examined, weighed, and measured. Normally, the placenta leaves within an hour after the birth of the baby.
Oncology may be here.
As in any organ of our body, in the placenta, malignant changes in cells can also begin. The most common chorioangioma is a pathological proliferation of villi in one cotyledon. This tumor is benign and does not metastasize. Surgery is usually not performed, since during labor, the formation is removed from the mother's body along with the placenta.
Close focus on the obstetrician
The condition of the placenta, its position and functions - this is the subject of close attention of the doctor. After all, the success of pregnancy and the health of the fetus largely depend on the child’s place. The following methods are used to diagnose the condition of the placenta:
- Ultrasound examination makes it possible to assess the condition, location and characteristics of the development of a child's place.
- Laboratory studies will help determine the level of placental hormones and the activity of certain enzymes in the blood of a pregnant woman.
- Dopplerometry will show the speed of blood flow in each of the vessels - the uterus, umbilical cord, fetus.
Summarize
The placenta is a unique organ that belongs to both the mother and the baby. Her role in the development of the fetus is invaluable. It is in the cotyledon of the placenta that the main borderline barriers between the blood of the mother and the child are located. And any disruptions in the functioning of this system are fraught with very serious consequences.