Question

Does trophoblast become placenta?

Answer 1

Trophoblasts are cells that make up the blastocyst's outer layer and are present four days after fertilisation in humans. They nourish the embryo and form a significant portion of the placenta.

Complete answer:
Trophoblasts are the cells that make up the outer layer of a blastocyst, which feeds the embryo and eventually becomes a major part of the placenta. They are the first cells to differentiate from the fertilised egg during the first step of pregnancy.

Following decidualization, trophoblasts play a significant role in embryo implantation and association with the endometrium of the maternal uterus. Two layers make up the trophoblast: an inner cytotrophoblast and an outer syncytiotrophoblast.

Undifferentiated cytotrophoblasts and completely differentiated syncytiotrophoblasts are the two cell populations present in villous trophoblasts. The syncytiotrophoblasts are a continuous layer of epithelial cells with specialised functions. They are in close contact with maternal blood and cover the entire surface of villous plants.

At 28 weeks of pregnancy, syncytiotrophoblasts have a surface area of about 5 square metres, rising to 11–12 square metres at term. The functional unit of maternal-fetal oxygen exchange and nutrient transport is the fully formed terminal villi.

Extravillous trophoblasts are formed when cytotrophoblasts in the tips of villi differentiate into another type of trophoblast. The placenta develops extravillous trophoblasts, which enter the decidualized uterus.

This procedure is necessary not only for physically connecting the placenta to the mother, but also for altering the uterine vasculature to enable the developing foetus to receive sufficient blood supply as the pregnancy progresses.

Note: Intrauterine growth restriction (IUGR) may cause an undersized foetus to develop poorly or even die. Placental dysfunction, caused by the inability of extravillous trophoblasts to reach and alter the uterine spiral arteries, is the primary cause of IUGR. As a result, the foetal atmosphere is under-oxygenated, and foetal development is stunted.