What are Trophoblast Cells?
Trophoblasts can be defined as cells that form the outer layer of a blastocyst. They are present four days post-fertilization in human beings. Trophoblast cells extend much-needed nutrients to the embryo and develop into a large portion of the placenta. They take shape during the preliminary stage of pregnancy. They are the first cells to differentiate from the embryonic egg to transform into extraembryonic structures that do not directly contribute to the embryo.
It is essential to remember that Trophoblast cells are an intriguing and enticing lineage of cells. They are specialized and particularized cells that redirect maternal physiology to support the support and growth of the fetus all on its own. We have to acknowledge that trophoblast cell biology is indispensable to understanding placental development and pregnancy-related diseases. The process of trophoblastic tissue specialization is reliant on external and internal environmental challenges. Now that we have briefly deliberated upon the fundamentals of trophoblast and what they are all about, let us analyze trophoblast functions.
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Trophoblast Functions
As we have already discussed, trophoblasts are specialized cells of the placenta that play a veritably pivotal role in embryo implantation and interaction with the maternal uterus. The core of placental villi encapsulates mesenchymal cells and placental blood vessels directly linked to the fetus circulation via the umbilical cord. The center is surrounded by two layers of trophoblasts and the syncytiotrophoblast and cytotrophoblast. The latter is a layer of mono-nucleated cells that live underneath the former. The syncytiotrophoblast comprises fused cytotrophoblasts that form a layer that covers the placental surface. It is in direct content with the maternal blood that reaches the placental surface.
Furthermore, syncytiotrophoblast facilitates the exchange of nutrients, wastes, and gases between the maternal and fetal systems. Thus, the trophoblast function is crucial in human gestation. Moreover, the cytotrophoblasts in the tips of the villi can separate into another type of trophoblast known as the extravillous trophoblast. We can understand extravillous trophoblasts as structures growing out from the placenta and penetrating the decidualized uterus. The entire process is crucial for physically attaching the placenta to the mother and for altering the vasculature in the uterus. The alteration enables adequate blood supply to the growing fetus as the pregnancy continues.
Cytotrophoblast and Syncytiotrophoblast – An Overview
We can understand cytotrophoblasts as the initial unfused trophoblast cells that engulf or cover the implanting blastocyst surface. In the late pregnancy placenta, this layer becomes squamous and discontinuous. Consequently, the syncytiotrophoblast cells become the primary cellular barrier. On the contrary, the syncytiotrophoblastic cells form by the trophoblastic reaction of rapidly dividing cytotrophoblastic cells. They are the primordial cellular barrier or interface between the maternal blood-filled spaces and the placental villi.
Syncytiotrophoblast cells secrete proteolytic enzymes that break down the extracellular matrix around cells. They also enable the passage of blastocyst into the endometrial wall and generate spaces to fill the lacuna with maternal blood. Later in the placental development, syncytiotrophoblast cells secrete HCG. Thus, we can analyze the two types of trophoblast stem cells. It is noteworthy to remember that trophoblasts of the human placenta differentiate along two pathways to give rise to extravillous cytotrophoblasts with invasive characteristics. They are implicated in the implanted process. And the second consequence is the villous trophoblast.
Significance of Trophoblast Cells
It is noteworthy to remember that the invasion of a particular type of trophoblast cells known as extravillous trophoblast cells into the maternal uterus is crucial for establishing pregnancy itself. The failure or malfunction of the trophoblast to invade sufficiently is critical in the development of cases of pre-eclampsia. Moreover, the invasion of the trophoblast too deeply may also result in conditions such as the placenta accrete, placenta accreta, and so forth. Lastly, trophoblast stem cells are cells that can regenerate and are similar to embryonic stem cells.
In conclusion, the topic of the trophoblast is an integral part of Biology. It is an indispensable part of the pregnancy process in human beings. Hence, everyone should know the basics of the topic. Various PDFs and study material on trophoblast and blastocyst are amply available to help you attain a firmer grasp on the subject.
FAQs on Trophoblast
1.What is a blastocyst?
We can understand blastocyst as a structure that is formed in the early development of mammals. It has an inner cell mass that consequently forms the embryo. The outer layer of the blastocyst comprises cells collectively known as the trophoblast. In human beings, blastocyst formation happens about five days after fertilization when a fluid-filled cavity opens up in the morula. The blastocyst has a 0.1 to 0.2 mm diameter and encapsulates 200 to 300 cells following rapid cell division of cleavage. After seven of the fertilization process, the blastocyst undergoes implantation – the embedding into the endometrium of the uterine wall. There, it further develops.
2. What is trophoblast invasion of arteries?
The trophoblast invasion of arteries is a novel model of in vitro fertilization. The extravillous trophoblasts invade the uterine wall and the spiral arteries, substituting for the vessel wall cells and creating a high-flow low-resistance vessel.
3. What is the meaning of cleavage?
We can understand cleavage as the mitotic division that begins when the zygote travels through the isthmus of the oviduct in the direction of the uterus and forms 2, 4, 8, 16 daughter cells which we know as blastomeres. The embryo with 8 to 16 blastomeres is known as a morula. It divides further as it moves deeper into the uterus and transforms into a blastocyst finally. The blastomeres in the blastocyst and arranged into an outer layer that we know as the trophoblast. The inner mass of cells attached to the trophoblast is known as inner cell mass. Lastly, the trophoblast layer gets attached to the endometrium of the uterus, and the internal cell mass divides to engulf the blastocyst. Hence, the blastocyst becomes embedded in the endometrium of the uterus, and the process is known as implantation.
