A trophoblast is a layer of cells. It forms the outer boundary of the blastocyst and is responsible for nourishing the embryo.
What is the trophoblast?
The trophoblast is a layer of cells and is the outer boundary of the germinal blastocyst in humans. Together with the placenta, it is necessary for the care of the embryo during the course of a pregnancy. During pregnancy, mother and child are dependent on certain substances (e.g. folic acid). This need is increased during pregnancy. In the early stages of pregnancy, the trophoblast also provides nutrition for the embryo with these important substances.
Anatomy and structure
On the 5th to 12th day after fertilization, the trophoblast forms from the blastomeres. Its cells grow into the mucosa of the uterus, where they then attach. It thus mediates the implantation of the embryo. and differentiates further into the cytotrophoblast (inner cell layer) and the syncytriotrophoblast (outer cell layer). In the course of pregnancy, parts of the amniotic membrane and the embryonic part of the placenta (placenta) develop from these layers. In principle, there is no permanent integration of the cells of the trophoblast into the maternal or fetal organism. Through them, only the transmission between the two biological systems takes place. Although they are so-called semi-allogeneic cells, the maternal immune system does not recognize them. In medicine, it has not yet been conclusively clarified how immunological tolerance of these biological mechanisms occurs. Conceivable factors include the formation of specific MHC class 1 antigens and the lack of formation of MHC class 2 antigens.
Function and Tasks
The trophoblast is the outer wall of the germinal vesicle in humans. In medical terminology, it is referred to as a blastocyst. The production of the trophoblast is regulated by the woman’s menstrual cycle. It consists of a layer of flat and polygonal cells. These are also called cytotrophoblast cells and correspond to an early chorionic epithelium. This is the outer layer of the amniotic sacs surrounding the embryo. The term chorionic epithelium can be derived from the Greek term for villous membrane. The task of the trophoblast is to establish contact with the mucous membrane of the uterus during implantation of the egg. Following this process, the trophoblast is transformed into a spongiotrophoblast. It is considered the so-called nutritional organ of the germ and can be compared to a sponge in purely external terms. With the help of enzymes, the mucous membrane of the uterus is softened by the trophoblast, allowing it to attach itself to it. The trophoblast thus serves to support the development of the embryo in the womb. Trophoblast cells develop from a single egg.
Diseases
Normally, during pregnancy, the trophoblast gives rise to the placenta and the membranes of the egg. However, complications can also occur. In this case, benign or malignant tumors mistakenly develop from certain parts of the tissue of the fertilized egg in women of childbearing age during or even after pregnancy. A benign trophoblast tumor is a partial or complete bladder mole. This is a disorder of the child’s development in the early stages of pregnancy. It occurs when the fertilization of an egg deviates from the norm. The cells of the trophoblast multiply uncontrollably, although they are supposed to form egg membranes and placenta. This results in the formation of bubbles the size of grapes and arranged in a cluster, which contain a light-colored fluid. The embryoblast, i.e. the later child, atrophies in the process, so that there is no normal pregnancy. Both partial and complete bladder mole are located exclusively in the uterus, without invading other tissues. According to statistics, a bladder mole occurs in about one in 2,000 to 3,000 pregnancies. In medicine, a partial bladder mole is referred to when fertilization of the egg occurs by two sperm cells instead of only one sperm cell. This results in the formation of amniotic fluid and the birth of a child, in which sometimes even a heartbeat can be detected.However, the cells of the trophoblast divide as often and as they want and not only as often as necessary for the development of the placenta and membranes. Most often, a miscarriage occurs between the 4th and 6th month of pregnancy. If we speak in medicine of a complete bladder mole, the egg is fertilized, but the mother’s genetic information is missing. Thus, there is no development of a child. Here, too, the cells of the trophoblast divide as often and as they want and not only as often as necessary. Already in the first weeks of pregnancy miscarriage is common here. A malignant trophoblast tumor is the so-called chorionic carcinoma. Under certain circumstances, an invasive bladder mole can also occur. Basically, after pregnancy, miscarriage or ectopic pregnancy, remnants of the trophoblast remain in the uterus. For reasons that have not yet been explained, these may divide uncontrollably and implant in the mucosa of the uterus. Via blood and lymphatic fluid, the tumor can spread throughout the body, resulting in the formation of metastases. In most cases, the formation of malignant trophoblast tumors occurs from a complete bladder mole. This results in either an invasive bladder mole (destructive bladder mole) or chorionic carcinoma (chorionic epithelioma). An invasive bladder mole can develop from 10 to 15 out of every 100 complete bladder moles, and it can also occur in one out of every 15,000 pregnancies. If it is not treated, it can develop into chorionic carcinoma. It usually occurs mainly after bladder moles, but rarely after normal pregnancies, ectopic pregnancies or miscarriages. According to statistics, chorionic carcinoma occurs in 2 to 3 out of 100 bladder moles and in one out of 40,000 pregnancies. The first signs of this very aggressive and fast growing tumor appear either immediately after birth or very often many years later. Metastases often form in the lungs, brain, liver, or even in the bones.
