Placenta

Placenta (synonym children's place - a body, which is formed during pregnancy and for communication between the mother and the fetus. Through the placenta during fetal development is the food, breathing the fetus, excretion of metabolic products.

placenta
Placenta in late pregnancy: 1 - fertile surface; 2 - maternal surface.

Placenta takes the form of a disk with a diameter of 15 - 20 cm, thickness of 2-4 cm and a weight of 500-600 g (1/6 of the weight of fruit). The surface of placenta, addressed to the fetus (fetus part), covered with amnion (see the Last), smooth, it is attached by the umbilical cord (see)which goes branching vessels (Fig., 1). Maternal part of the surface of a dark red color, divided into segments - cotyledon (Fig., 2)covered desiguales shell (see).
Fruit a part of the Isthmus is formed chorionic plate (shell). From chorionic plate depart villi. Each hair is supplied with capillaries from umbilical vessels. Villi placenta full-term fetus is covered with a layer of syncytium.
Maternal part of the placenta (basal plate) is formed compact layer of the falling of the shell and layer trophoblast cell. From the basal plate depart partitions (septi), which divides the placenta into slices; septi not reach chorionic plate. Through the basal plate from the wall of the uterus placenta takes place from 180 to 320 spiral arteries. Coming on these vessels maternal blood pouring out between the fibers in the so-called majorsince space (the space between basal and chorionic plates). From the placenta of the mother's blood flowing in the regional sinus and in a vein in the basal plate. Thus, in the placenta are two blood flow: one parent in the system of the uterus - majorsince space - uterus and the second in the system fruit - umbilical - fibers - the umbilical cord. The blood of the fetus and the mother's blood won't mix and separated by a syncytium covering villi, and endothelium their capillaries. This membrane is conventionally called placental barrier. The contact surface of fibers with the mother's blood is very large - 6.5 m2.
Oxygen to the fetus comes from flowing into the placenta blood of the mother. In placenta part substances pass through cell and tissue membrane of the mother's blood in the blood of the fetus and back by simple diffusion; in addition, and active transport. So, water exchange occurs through P. in both directions very quickly (3500 ml/hour). The transition of carbohydrates, fats and proteins through the placenta is the result of a complex biochemical processes involving enzymes placenta. Some medicinal substances penetrate through the placental barrier, it depends on their molecular weight, and their lipid solubility.
The placenta produces chorionic gonadotropin (see Gonadotropic hormones), close on properties to pituitary gonadotropin. The human chorionic gonadotropin secretion in the first weeks of pregnancy is used for hormonal diagnostics of pregnancy (see Elgama - Condeca reaction, Galli - Mainini reaction). The secretion of the hormone reaches its maximum by the third month of pregnancy. During pregnancy the placenta allocates estrogenic hormones (see Sex hormones, progesterone, identical to the hormone yellow body; the secretion of progesterone increases progressively, starting from the third month until the end of pregnancy. Progesterone reduces the excitability of the myometrium.
Pathology. In severe (edema) in the form of hemolytic disease of the fetus, the placenta is very high and the ratio of its weight to the weight of fruit is 1 : 3 and 1:2; at every birth must weigh not only the newborn, but also the placenta with shells of the fetus. When edematous form of hemolytic disease of the fetus, the placenta has a pale red, swollen, maternal surface of grundrechte; in syphilis in some cases, the placenta can also be swollen and large. Often in the placenta found white heart attacks - well demarcated areas of necrosis Vorsin. Heart attacks are often observed in late toxicosis of pregnancy; if a significant number of heart attacks can occur fetal loss. Often a normal placenta on the maternal side are the sediment grains lime; they are always available in advanced pregnancy.
In obstetric practice of great importance anomalies of placental attachment (see the placenta Previa).
Another form of the disorder is premature detachment normally attached to the placenta. There are two forms of detachment - light and heavy. When the first detachment of the placenta is at low over, capturing one or two cotyledon; comes with moderate external bleeding; the General condition of the pregnant woman and the fetus is not disturbed. In severe external bleeding may not be; the result of placental abruption on the large surface of a large retroplatsentarno hematoma. A pregnant woman develops severe shock; in the case of placental abruption half the surface comes intrauterine fetal death. Placental detachment occurs when the combination of pregnancy with hypertension and at late toxicosis. Pregnant supposed detachment of the placenta must be urgently and carefully (stretcher) delivered in maternity hospital, where her in her testimony can be made caesarean sections and blood transfusions. Cm. also Succession period, Postpartum period.

Placenta (from lat. placenta - bread; synonym children's place - a body, which is formed during pregnancy and ensuring communication between organisms mother and fetus. P., development of the fetal membranes, mainly from villous (villi) and accrete with them decidual shell (see) of the uterus, is the main part of the placenta. Through the placenta is the food, breathing the fetus and the removal of metabolic products.
The development and structure of the placenta in various animal species are very diverse. P. person belongs to gemorroidalnom type, as trophoblast ovum destroys the endothelium maternal capillaries, and chorionic villi (see) derive nutrients and oxygen from the mother's blood.
In the first week of development of the ovum especially growing trophoblast (see Embryo). In the distal ends of the fibers of mesenchyme't grows and produces cell clusters. Cells bordering decidual tissue and miscible with its elements are the cells cytotrophoblast (efficiency UNESCO-Stroganov). Fibers that connects to the decidual shell, called a docking or anchoring (Fig. 1). By the end of the third month villi smooth chorion atrophy, and branched chorion begins to form P. P. Growth occurs due to their intensive branching fibers. There are fruit and maternal part (side) P. Fruit formed part of chorionic plate and covered with amnion; it is attached by the umbilical cord with their blood vessels. In chorionic plate are branches of the vessels of the umbilical cord and depart from it stem villi. Maternal part of the Isthmus (the basal plate) is formed by compact layer falling shell and layer trophoblast cell. Between basal and chorionic plates is majorsince space (Fig. 2), which is circulating in maternal blood.

Fig. 1. Anchor fibers and cell clusters of cytotrophoblast.
Fig. 2. The scheme of the structure of the placenta in Steve: 1 - decidual shell; 2 - placental wall; 3 - chorionic plate; 4 - barrel villi; 5 - amnion; 6 - umbilical vessels; 7 - majorsince space.
Fig. 3. Cross section through the hair in early pregnancy: 1 - syncytium; 2 - kidney-shaped razreshenia of syncytium; 3 syncytial giants; 4-the layer of cells Langhans; 5 - vessels villi.
Fig.4. The partition wall between cotyledonary in its point of attachment to the basal plate.

With the development of pregnancy trophoblast cells of the basal plate seats are fully degeneration, and then fibrinovy layer dissociates majorsince space; the latter by chorionic plate is bordered by a layer of cells Langhans (Fig. 3).
After four months in the placenta is formed partitions (septae), starting from the basal plate in the direction of chorionic, but not getting to it (Fig. 4). These partitions are divided P. on the share (cotyledonis)that are visible from the maternal side P. (on average, 16-20). Partitions divide majorsince space is not full, and under chorionic plate it is a whole (Fig. 5).

Fig. 5. Circulation in majorsince space (Spanner): 1 - uterine artery; 2 - majorsince space; 3 - marginal sinus; 4 - parent Vienna; 5 - placental barrier.

Placenta full-term fetus is oblate body, with a diameter of 15-20 cm, thickness up to 3 cm and a weight of 500-600 g
In majorsince space the blood comes from the utero-placental vessels, spiral arteries, flowing back down to the uterus on uteroplacental veins. Blood in majorsince space circulates slowly, as uterine-placental vessels are relatively small, and majorsince space is vast and the pressure within about 10 mm RT. Art.
In majorsince space shipped villi of prisoners in them the ultimate ramifications of vessels fruit (Fig. 6). Metabolism, including gas exchange occurs through the wall of the capillary fibers and their top epithelium.
Between circulating in the blood vessels of the villi blood of the fetus and majorsince space no message. The blood of the fetus and the mother circulates in independent from each other systems and nowhere is mixed.
In the systemic circulation pregnant included uterine-placental blood flow.


Physiology. Placenta exercises between the mother and the fetus all variety of metabolic processes occurring through the surface of chorion villus. Towards the end of pregnancy, the surface of the fibers reaches 6000-10 000 cm2, and the total length of 50 km. Morphological and functional features P., allowing to adjust the penetration of various substances from the blood of the mother to the fetus and back, is considered as the placental barrier. In Petrograd there are mechanisms in support of the transition from the mother to the fetus different substances necessary for its development. The fetus receives from the mother via P. oxygen, nutrients, water, electrolytes, vitamins, antibodies, and passes the mother of carbon dioxide and wastes. P. also produces several hormones, inactivates and destroys other, activates enzymes. In the placenta found many of the enzymes that break down carbohydrates, proteins and fats, as well as respiratory enzymes and all known vitamins (especially); proven ability P. synthesize glycogen, acetylcholine (E. M. Berkovich). All this turns on, in a unique education that simultaneously performs the functions of the lungs, intestines, liver, kidneys and endocrine gland.
The barrier that separates the blood of the mother and fetus in majorsince space consists of epithelial trophoblast or syncytium covering villi, connective tissue fibers and endothelium their capillaries. In terminal hairs many capillaries are placed right under the syncytium, and barrier when it consists of only two single-cell membranes.
In placenta complex mechanisms that determine the process of placental transmission. Syncytium and cytotrophoblast that make up the cover of the villi P., have high activity against resorption, enzymatic degradation and synthesis of many complex substances. Perhaps these derivatives trophoblast involved in the regulation of the transfer of substances from the mother to the fetus and back (C. I. Bodyagina). P. able to inhibit or delay the transition of certain substances from the mother to the fetus and from the fetus to the mother. However, the barrier function of P. limited. If the transition gases, proteins, fats, carbohydrates and other substances, constantly present in the blood of the mother, are regulated fairly precise mechanisms, developing in Petrograd in the process of its evolution, in relation to substances that enter the body by accident (drugs, toxins, and other), the electoral function P. adapted to a lesser extent, and the mechanisms governing their transition, imperfect or lacking.
Barrier function P. carried out only under physiological conditions. It is important to note that a gradual thinning of syncytium with increasing gestational age increases the permeability of the placenta. In syncytial cover fibers are formed holes, gaps (efficiency UNESCO-Stroganov).
Exchange of gases (oxygen, and other) and true solutions through the placental membrane is under the laws of osmosis and diffusion due to the difference in partial pressure in the blood of the mother and fetus; the transition of proteins, fats, carbohydrates and other substances as a result of complex biochemical processes with the participation of P. possessing diverse enzymatic functions.
In the blood of the mother and fetus has a different concentration of potassium, sodium, phosphorus and other substances. The mother's blood richer in proteins, lipids, neutral fats, glucose, in the blood of the fetus more protein-free nitrogen, free amino acids, potassium, calcium, inorganic phosphorus and other
The rate of passage of drugs through the placental barrier is associated with the degree of ionization and lipid solubility medicationovernight molecules; unionised substances with high solubility in lipids penetrate the barrier quickly. Placental barrier protects the fetus from penetration of harmful substances only partially. Penetrates through the placenta drugs, alcohol, nicotine, cyanide, mercury, arsenic, antibiotics, vitamins, hormones, some antibodies, viruses, toxins and other Permeability of placental barrier for harmful substances and bacteria increases with pathological changes P. associated with complications of pregnancy and childbirth, and also for damage to the villi microbes and their toxins.
Placenta is a temporary gland of internal secretion, producing the gonadotropins, estrogens and progesterone. Education and P. gonadotroponah hormones (see) - cells Langhans and clusters of trophoblast cells.
The estrogen produced by P. trophoblast first in a small amount, and further production of hormones increases. In a Mature placenta find mostly estriol, in a smaller number of estrone and even fewer are of estradiol. Estrogen affect the anterior pituitary gland, interstitial the brain, and the autonomic nervous system of the mother, and also on a number of vital processes and especially on liver function.
Progesterone until the 4th month of pregnancy is produced luteum of the ovary and in the future with the extinction of the yellow body mainly P. the Increase progesterone as the pregnancy is confirmed by the increase of the number of pregnandiol excreted with urine. Estrogen and progesterone, especially their quantitative ratio, are of great importance for physiological pregnancy and fetus (see Pregnancy), offensive and regulation of labor activity (see Childbirth).