What Is Trophoblast?

Trophoblasts are cells with trophic function, which come from the trophoblast outside the embryo. The trophoblast cells grow rapidly, forming many hairy protrusions on the surface of the embryo sac, called "villi".

Trophoblasts refer to the cells with trophoblast function from the trophoblast outside the embryo. The trophoblast cells grow rapidly, forming many hairy protrusions on the surface of the embryo sac, called "villi".

The trophoblast started with only one layer of flat cube-shaped cells. When the villi were formed, this layer of cells gradually differentiated into two layers. The inner layer and interstitial contact, formerly called "Langhans cells", now called "cytotrophoblasts". The outer layer is in contact with the uterine decidua. It was formerly known as "synaptic cell" and is now called "syncytiotrophoblast". It is further understood that normal trophoblasts have certain unique biological characteristics that are closer to malignant tumors than normal tissues. Trophoblasts invade the endometrium, myometrium, and spiral arteries by centrifugation from the area surrounding the embryo sac, establishing the uterine placental circulation. Trophoblasts invade the blood vessels and spread widely in the blood throughout the normal pregnancy, mainly to the lungs, and disappear after delivery. The trophoblasts that cover the chorionic villi are called "villous trophoblasts". The trophoblasts in other parts of the uterus are called "external villous trophoblasts". The extravillous trophoblasts form a trophoblast column that traverses the villus space from the base where the villi are anchored; infiltrating the decidual membrane surrounding the base of the embryo sac to form a trophoblastic shell that partially evolves into a smooth villous epithelium; invades the spiral arteries of the placental bed Infiltrate the muscle layer below the implant site.

Trophoblasts are composed of heterogeneous cell populations, and there are three distinct types of morphology, namely: cytotrophoblasts (CT), syncytiotrophoblasts (ST), and intermediate trophoblasts (IT).

Cell trophoblasts (CT) are composed of uniform, polygonal to oval-shaped epithelial cells with a single, round nucleus, few cytoplasm, transparent or granular, clear cell boundaries, and active mitosis.

Synovial trophoblasts (ST) are composed of multinucleated, cytoplasm-rich, double-stained, or eosinophilic cells that contain vacuoles of varying sizes during the first two weeks of pregnancy, some of which form pits. Synaptic trophoblasts lack mitosis because they are the most differentiated type of trophoblast.

Intermediate trophoblasts (IT) are mostly composed of mononuclear cells, which are larger than cytotrophoblasts. However, multinuclear cells and intermediate trophoblasts can be seen as round or polygonal. They can be spindle-shaped outside the villi, and the cytoplasm is clear. Rich, double-stained or eosinophilic, the nucleus is round and leaf-like, oval, chromatin is irregularly distributed, and mitosis is rare. Intermediate trophoblasts and cell trophoblasts, synaptic trophoblasts have certain common characteristics, but the characteristics of light microscopy, ultrastructure, biochemistry and function are obviously different from cell trophoblasts and synaptotrophs.

1. Normal villi and trophoblasts

Trophoblasts come from the trophoblast outside the embryo. Trophoblast cells grow rapidly

Gestational trophoblastic disease (GTD) is a group of diseases that gradually transform from benign to malignant, that is, benign hydatidiform mole can be transformed into erosive hydatidiform mole and choriocarcinoma. The trophoblast itself has the ability to infiltrate into the mother's uterine wall. When the growth of the trophoblast is precise, the air-conditioning control is broken to form a gestational trophoblastic tumor (GTT). Therefore, the disease is highly destructive, can be disseminated through blood transport very early, and is widely transferred, threatening women's lives. As more chemotherapeutics are used for the treatment of gestational trophoblastic diseases, the cure rate of trophoblastic tumors reaches 80% to 90%, making it one of the earliest curable malignancies. Because the etiology of trophoblastic tumors is unknown, early correct diagnosis, determining the nature of trophoblastic tumors, and timely chemotherapy, judging the effect of chemotherapy, and predicting the outcome of the disease are the keys to treatment. But until now, there is no objective indicator to predict the malignant transformation of hydatidiform mole. With the progress of molecular biology research, people are trying to predict the early diagnosis of hydatidiform malignancy at the molecular level in order to treat it in time. The most fundamental biological characteristic of tumor cells is the blocked differentiation and unrestricted proliferation. The proliferation activity is closely related to the biological behavior and prognosis of tumors. The degree of proliferation of malignant tumor cells is much higher than that of normal tissues and benign tumors. The higher the proliferation index, the higher the degree of malignancy. The expression of cytotrophic markers such as Ki-67, proliferating cell nuclear antigen, and nucleolar composition-associated silverophilin in trophoblastic diseases is now used as an indicator to determine the level of trophoblast proliferation, and the degree of proliferation in trophoblastic diseases The relationship with its malignant degree is reviewed in order to provide ideas for the research to predict the outcome of gestational trophoblastic disease. ^[1]