The placental barrier separates the mother’s blood circulation from that of the baby. Through this tissue filter, the two blood circulations operate independently of each other.
What is the placental barrier?
The placental barrier separates the mother’s bloodstream from that of the baby. Through this tissue filter, the two blood circuits operate independently of each other. Once a fertilized egg implants in the lining of the uterus, it is completely supplied by the mother’s body. The oocyte’s power reserves are now depleted and it relies on being kept alive by the uterine mucosa. Within a few weeks, this mucosa develops into a placenta, which adheres to only one part of the uterus and remains connected to the baby by the umbilical cord. Initially, the blood circulations of mother and child are not yet separated – this only occurs through the formation of a placental barrier. Histologically, it consists of several layers and is a thin separating membrane located at the chorionic villi. This is where the exchange of substances between mother and child takes place, because the placental barrier is there to allow only those substances from the mother’s bloodstream into the fetal bloodstream that the child needs. These are oxygen or nutrients, for example.
Function and task
In the first days of life of the fertilized egg, it does not yet need any separation from the maternal body. Over time, however, independent circulation of the unborn child becomes important, which is why this is one of the first functions that the placenta develops. The placental barrier serves both as a protective barrier and as a transport route. There are a number of transport mechanisms by which a substance can pass from the maternal blood to the child, such as diffusion or pinocytosis. These are each intended for different substances to pass through the placental barrier to the baby. Diffusion, for example, serves to nourish the unborn baby. In this way, it receives nutrients or oxygen from the maternal circulation. Pinocytosis, on the other hand, is intended to transfer IgG immune cells from the mother to the baby. These immune cells are produced in humans about 6 weeks after an infection has been overcome and ensure that it cannot re-emerge as quickly. Since a baby will not be able to produce its own immune cells shortly after birth, it receives exactly these long-acting immune cells from the mother. The baby can therefore only be immune to diseases to which its mother is also immune. This protection from birth until the formation of its own immune system is called nest protection and it is one of the most important functions of the placental barrier, along with nutrition. However, since not everything is allowed to reach the baby either, the placental barrier protects the unborn child from the transmission of other blood components. These are not allowed to pass through the placental barrier and in this way cannot reach the baby.
Diseases and medical conditions
The placental barrier and its function are closely related to the healthy development of the placenta itself, called placentation. If a placental disorder occurs during this development, the placental barrier may be affected in some circumstances, causing problems for both mother and baby. In most cases, the placental barrier is nevertheless intact enough to ensure separation between maternal and fetal blood and correct filtering of substances. However, after birth or, in the worst case, even before, placental abruptions may occur, accompanied by heavy bleeding that immediately triggers the birth of the child. Depending on the degree of development of the child, it is possible to save it. For the mother, placental abruption poses a significant risk due to blood loss. She needs immediate medical help in this case – and a neonatologist is then also crucial for a premature baby. If the placenta is perfectly healthy, microtrauma to the placenta can still always occur. This means that the placenta has experienced a minimal injury, for example due to a wrong movement, a great physical strain or even an unintentional bump against the abdomen in everyday life. The mother does not notice the microtrauma, but there is a small tear in the placental barrier and fetal blood enters the maternal circulation. This is of concern if the mother is Rh negative and the child is Rh positive.Your immune system will then start to produce antibodies against your baby’s rhesus-positive blood. The first baby for whom this happens will be born perfectly healthy. Usually, however, only the first pregnancy goes well. In a second pregnancy, when the baby is again Rh-positive, the mother’s immune system will react more quickly and begin to reject the baby because the immune system recognizes it as an invader. With the help of drugs that suppress these antigens in the mother’s blood, it is nevertheless possible for the woman to become pregnant again by the same man and give birth to the child in good health. However, it must be recognized in time that this special case exists. Even a healthy placental barrier, however, allows substances to pass to the child that can harm it. We are talking about alcohol, components of cigarettes, drugs and some medications. This is why it is so important for pregnant women not to consume any of these substances and to take medications only under the supervision of a doctor, in order to prevent congenital damage to the child.
