biology

Trophoblast

Trophoblast is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Trophoblast rather than just read about it. In short: The trophoblast (from Greek trephein: to feed; and blastos: germinator) is the outer layer of cells of the blastocyst. Trophoblasts are present four days after fertilization in humans.

Key takeaways

Trophoblast belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Trophoblast to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Trophoblast from memory before moving on to harder problems.

Reference excerpt

The trophoblast (from Greek trephein: to feed; and blastos: germinator) is the outer layer of cells of the blastocyst. Trophoblasts are present four days after fertilization in humans. They provide nutrients to the embryo and develop into a large part of the placenta. They form during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg to become extraembryonic structures that do not directly contribute to the embryo. After blastulation, the trophoblast is contiguous with the ectoderm of the embryo and is referred to as the trophectoderm. After the first differentiation, the cells in the human embryo lose their totipotency because they can no longer form a trophoblast. They become pluripotent stem cells.

Structure

The trophoblast proliferates and differentiates into two cell layers at approximately six days after fertilization for humans.

Function Trophoblasts are specialized cells of the placenta that play an important role in embryo implantation and interaction with the decidualized maternal uterus. The core of placental villi contain mesenchymal cells and placental blood vessels that are directly connected to the fetus’ circulation via the umbilical cord. This core is surrounded by two layers of trophoblasts, the cytotrophoblast and the syncytiotrophoblast. The cytotrophoblast is a layer of mono-nucleated cells that resides underneath the syncytiotrophoblast. The syncytiotrophoblast is composed of fused cytotrophoblasts which then form a layer that covers the placental surface. The syncytiotrophoblast is in direct contact with the maternal blood that reaches the placental surface. It then facilitates the exchange of nutrients, wastes and gases between the maternal and fetal systems. In addition, cytotrophoblasts in the tips of villi can differentiate into another type of trophoblast called the extravillous trophoblast. Extravillous trophoblasts grow out from the placenta and penetrate into the decidualized uterus. This process is essential not only for physically attaching the placenta to the mother, but also for altering the vasculature in the uterus. This alteration allows an adequate blood supply to the growing fetus as pregnancy progresses. Some of these trophoblasts even replace the endothelial cells in the uterine spiral arteries as they remodel these vessels into wide bore conduits that are independent of maternal vasoconstriction. This ensures that the fetus receives a steady supply of blood, and the placenta is not subjected to fluctuations in oxygen that could cause it damage.

Clinical significance The invasion of a specific type of trophoblast (extravillous trophoblast) into the maternal uterus is a vital stage in the establishment of pregnancy. Failure of the trophoblast to invade sufficiently is important in the development of some cases of pre-eclampsia. Invasion of the trophoblast too deeply may cause conditions such as placenta accreta, placenta increta, or placenta percreta. Gestational trophoblastic disease is a pregnancy-associated concept, forming from the villous and extravillous trophoblast cells in the placenta. Choriocarcinoma are trophoblastic tumors that form in the uterus from villous cells. Trophoblast stem cells (TSCs) are cells that can regenerate and they are similar to embryonic stem cells (ESCs) in the fact that they come from early on in the trophoblast lifetime. In the placenta, these stem cells are able to differentiate into any trophoblast cell because they are pluripotent.

Additional images

See also Syncytiotrophoblast Hydatidiform mole

References

External links Swiss embryology (from UL, UB, and UF) iperiodembry/carnegie02

Illustrations

Worked examples

Example 1 — a first encounter with Trophoblast

Start with the simplest possible case. Write down what Trophoblast claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Trophoblast before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Trophoblast ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Trophoblast

In research: Trophoblast appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Trophoblast in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Trophoblast is common in secondary-school and first-year university syllabi. It links to neighbouring topics Animal developmental biology, Placentation, so understanding it makes those chapters shorter.
In everyday life: Look for Trophoblast outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Trophoblast in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Trophoblast means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Trophoblast out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Trophoblast in simple terms?

The trophoblast (from Greek trephein: to feed; and blastos: germinator) is the outer layer of cells of the blastocyst. Trophoblasts are present four days after fertilization in humans.

Why does Trophoblast matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Trophoblast?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Trophoblast.