Placenta, placenta

English: placenta

Also read:

  • Diseases of the placenta


The plaster cake (placenta) represents an organ created during pregnancy, which consists of a child and a maternal part. The placenta performs numerous functions.
It is used for nutrition and the supply of oxygen to the child, it also produces various hormones and is used for the exchange of substances. Usually the placenta is disc-shaped with a thickness of about 3 cm and a diameter between 15 and 25 cm. It weighs around 500g.
If the placenta is intact, there is no contact between maternal and infant blood.

Development and structure of the placenta

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During the early development of the fertilized egg cell differ from the 4th day after fertilization two different types of cells that Embryoblasts and the Trophoblasts.
The trophoblasts are important for the development of the placenta, in particular the cells that emerge from them are called syncytiotrophoblasts. The cell cluster of the syncytiotrophoblast loosens on the 9th day after fertilization and forms small cavities (Lacunae). Since the fertilized egg implanted in the Uterine wall the small maternal blood vessels (capillaries) of the uterine muscle layer are enlarged and congested. This causes so-called sinusoids to form. The increasingly growing syncytiotrophoblasts gnaw on the maternal sinusoids, so that maternal blood seeps into the cavities. The syncytiotrophoblasts develop into villi, which transform and finally at the end of the third week become tertiary villi, in which children's blood vessels are formed.

Of the Plaster cake consists of a child and a maternal part. The maternal portion is made up of the muscular layer of the uterus educated. The child's part is made up of villi-rich egg skin (Chorion frondosum), which is located under the child and which consists of the above-mentioned cells, the trophoblasts.
Between these two parts there is a space which is filled with about 150-200 ml of maternal blood. This blood comes from maternal vessels in the uterine wall. In the blood-filled space there are many villi with their ramifications, which are then referred to as villi trees.
These villi trees are washed around by the mother's blood, so that the exchange of substances between mother and child can take place on their surfaces due to various transport mechanisms. It is important, however, that about the whole pregnancy the maternal blood remains separated from the child's blood by a layer of cells. This filter membrane is therefore also called the placental barrier.

The placenta consists of up to 38 lobules (cotyledons) in the direction of the maternal part, each of which houses at least two of these villi trees and which are connected to one another.
The placenta has its final structure by the 14th week of pregnancy (SSW). It continues to grow in thickness into the 5th month of pregnancy, while its area continues to increase after the 5th month of pregnancy and finally reaches a diameter of 15 to 25 cm. In terms of shape, the placenta is in most cases a disk-shaped structure. However, other shapes are also known. The placenta can be lobed, divided, formed with secondary lobes or belt-shaped. Only a diffuse distribution of the villi is extremely rare.

Functions of the placenta

Localization of the placenta

An important function of the placenta is the exchange of substances between mother and child.
In particular, water and oxygen from the mother get into the child's blood vessels due to differences in concentration. These vessels all ultimately unite in the vein of the umbilical cord (Umbilical vein), which carries the nutrient- and oxygen-enriched blood into the child's body.

Read more on the topic: Placental insufficiency

It is important here that the blood bypasses the liver so that the substances supplied are available to the entire organism and not all of them are used up by the liver. Sugar (glucose), proteins (amino acids and proteins) and fats also get into the child's blood with the help of various transporters in the placenta. Particularly noteworthy is the uptake of a certain type of antibody (immunoglobulin G), which guarantees the unborn child a certain protection against certain infections.
Nevertheless, some bacteria and viruses can penetrate the placental barrier and get into the child's organism. Due to this transition, the unborn child can still contract one or the other infection, especially caused by viruses, and become ill. Some drugs also enter the child's body through the placenta. For this reason, it is very important to be careful not to take such medications during pregnancy, as they can harm the child's development

Learn more at: Placental detachment after childbirth

Substances that the child excretes pass through two arteries in the umbilical cord (Umbilical arteries) back into the placenta and can there be released into the maternal blood via the villi. The mother can completely break down or remodel such waste products and remove them from her body.

The second major job of the placenta is to produce the large amounts of hormones that are needed during pregnancy and cannot be made by the mother's glands. On the one hand, the female sex hormones progesterone and estrogen are produced. Progesterone promotes breast development, milk production (lactogenesis) and inhibits the contraction of the muscles of the uterus. The growth of the breasts and uterus is due to the effects of estrogen. The concentration of estrogen in the maternal blood and urine depends on the child's vitality, as it converts precursor substances. However, today this method is hardly of any importance when examining pregnant women and their children.

Another very well-known hormone is the so-called human chorionic gonadotropin (HCG). It ensures that the muscle layer of the uterus with the fertilized egg cell is not shed. It also causes egg cells to mature in the ovaries in a female child and the testicles to descend into the scrotum in male children.
In practice, this hormone is used to prove pregnancy with the help of a pregnancy test. Because it can already be detected in high concentrations in the urine of the mother during early pregnancy.

In addition, the human placental lactogen (HPL) is formed, which provides fats to supply the mother with energy and reflects the functional state of the placenta, and the human chorionic thyroidotropin (HCT), the function of which is not yet fully understood.

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