The Amnion and the Umbilical Cord: Structure and Function

The Amnion and the Umbilical Cord: Structure and Function
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  • 0:01 Prenatal Environment
  • 1:08 Amnion
  • 4:24 Umbilical Cord
  • 5:24 Lesson Summary
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Lesson Transcript
Instructor: Natalie Boyd

Natalie is a teacher and holds an MA in English Education and is in progress on her PhD in psychology.

The prenatal environment is an important part of an embryo's development. Watch this lesson to find out more about the prenatal environment, including the importance of the amnion and umbilical cord and what they do.

Prenatal Environment

Imagine for a moment that you are floating out in space. All around you is a vast area, and you are tiny in comparison.

Not only are you tiny, you are also vulnerable. Meteors and other space debris fly past you. The lack of gravity allows you to float, but that also means that you can't control where you go. At times, the space you float in is very, very hot, and at other times, it's freezing cold.

Believe it or not, that's pretty close to what the prenatal environment, or the space surrounding an embryo in its mother's body, is like for a baby. The world is a vast place compared to an embryo that may only be a few cells large, and even the mother's body can present challenges for a prenatal baby.

But, just as you might have a spacesuit or a spaceship to help protect you and make sure you have what you need in space, an embryo in its mother's uterus also has certain things that can help protect it and provide it with all it needs. Let's examine two such protective elements: the amnion and the umbilical cord.


So, you're floating about in space. Everything is beautiful, and you love the view. But even a tiny pebble hurtling through space could cause you serious damage. Not only that, depending on how close you are to a sun, the temperature could be way too hot or way too cold for you to survive.

Just like someone floating about in space, an embryo is tiny and vulnerable. It needs protection and space to move and develop from a few cells into a baby ready for the world.

The amnion is a protective sac that surrounds a baby in the mother's womb. It protects against foreign objects and temperature swings in the womb.

Early in the pregnancy, the amnion is very close to the embryo. But a month or so into the pregnancy, the amnion begins to fill up with a fluid known as amniotic fluid. As it fills up, it expands. Think about a balloon filling up with water, and you can kind of picture what happens to the amnion as the pregnancy advances.

The embryo, too, develops and grows larger, but the amnion expands more rapidly so that there's more space between it and the embryo. Eventually, the baby will float inside the balloon-like amnion, which protects it and allows it to grow and develop safely.

To understand the way the amnion develops, let's go back to space for a moment. You're floating around in space, and you need protection. Imagine that you have a spacesuit on that gives you some protection.

But that spacesuit only gives you a little protection, so after a few weeks, it begins to grow around you. Slowly, it transforms into a spaceship. Now you have more breathing room; you can move around more than you could when you were just in the spacesuit. Not only that, but you have a little more protection, since whatever comes in contact with the outside of the spaceship is further away from you than when it was just the spacesuit.

That's pretty much what happens with the amnion: it starts out very close to the embryo, but by the fourth or fifth week of pregnancy, it has expanded to be more like a spaceship than a spacesuit.

Let's say that there's a larger ship outside of yours. They know that you are safe within your spaceship, but they're a little worried about air quality. They want to make sure that you're ok, so they pipe some of the air out of your spaceship - not a lot, just a little - and test it to make sure that everything is good.

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