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Author: Amanda Soderlind

Identify characteristics of the placenta and other structures associated with the baby's nourishment.

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Source: Video and Images Created by Amanda Soderlind

Video Transcription

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Welcome to this lesson on embryonic membranes.

Today we are going to be discussing the various membranes that are associated with fetal development.

We're going to be using and labeling this diagram for this lesson today.

We're actually going to start by labeling the placenta. These are all different membranes that are within a womb that are all involved in a certain way with a developing fetus.

The placenta, basically what it does is, it provides nutrients and oxygen to an embryo or fetus, and it carries away waste through these blood vessels. It's basically the lifeline, kind of, between the mother and the child, providing those nutrients and that oxygen that it needs, and then also carrying the waste away for the fetus through these blood vessels.

The placenta is actually connected here to the umbilical cord. The umbilical cord, as I mentioned, attaches to the placenta to deliver those nutrients and that oxygen that I mentioned, and also to carry away the waste. It's attached to the placenta and to the fetus, and it's basically just composed of these blood vessels.

Inside here we have amniotic fluid. In this area here is actually where the developing fetus or embryo would be. I didn't draw it in this diagram just for simplification reasons, but it would be in this open area here within the amniotic fluid.

The amnion is this layer here, and basically it's the sac that encloses the embryo, that's filled with the amniotic fluid. This amnion, this sac and the fluid, basically provides insulation and protection for the developing fetus or embryo.

The next layer that we have here is the chorion. The chorion is the outer membrane that provides protection, and it also secretes HCG, human chorionic gonadotropin, which prevents the breakdown of the endometrium.

Some other structures that we have associated with this, that aren't directly labeled on this diagram are the allantois. This structure gives rise to blood vessels of the umbilical cord, so it's kind of a part of the placenta that gives rise to these blood vessels that compose the umbilical cord.

The yolk sac is another structure. It's a membrane that produces early blood and germ cells, and parts of the embryo's digestive tube, but it's not-- it's not a membrane that stays around during the entire development. It actually disintegrates quite a bit earlier on.

And then here we have the cervix. So once the baby is ready to be born, it would actually move through the cervix and then to the outside of the body as it's being born.

This lesson has been an overview on various embryonic membranes, and their structure and function.

Terms to Know

An extension of the yolk sac, the allantois provides oxygen to and removes waste from the early embryo; eventually, the allantois's blood vessels will become the umbilical cord's blood vessels. The amnion, chorion, yolk sac, and allantois together form the protective sac that encloses the embryo within the uterus.


A sac or distinctive pouch that encloses the embryo and is filled with amniotic fluid that cushions and protects the embryo. The amnion, chorion, yolk sac and allantois together form the protective sac that encloses the embryo within the uterus.


An outer membrane around the fetus that protects the fetus, absorbs blood from the mother to be transferred to the embryo and secretes HCG to prevent endometrial breakdown. The amnion, chorion, yolk sac and allantois together form the protective sac that encloses the embryo within the uterus.


The blastocyst consists of the thin outer layer of cells (the trophoblast) surrounding a cavity within which is the inner cell mass (which will become the embryo). The trophoblast becomes the placenta, which connects the fetus via the umbilical cord to the uterus. The placenta provides nutrients, gas exchange and waste elimination via the mother's blood supply.

Umbilical Cord

The cord that connects the embryo to the placenta, the umbilical cord carries nutrients to the child and wastes away.

Yolk Sac

A membranous sac attached to the embryo that provides early nourishment and develops the cardiovascular system; the yolk sac eventually disintegrates. The amnion, chorion, yolk sac and allantois together form the protective sac that encloses the embryo within the uterus.