The Placenta and the Fetus: Structure and Function

Your next lesson will play in 10 seconds
  • 0:05 Placenta Structure and…
  • 1:40 Blood Flow and Nutrients
  • 3:38 Trophoblast Differentiation
  • 4:43 Lesson Summary
Create An Account
To Start This Course Today
Used by over 10 million students worldwide
Create An Account
Try it free for 5 days
Lesson Transcript
Instructor: Joshua Anderson
Have you ever wondered how a baby eats before it's born or if babies go to the bathroom while still inside their mother? In this lesson, you will learn about the placenta and how it works to ensure a fetus stays well-nourished and healthy before birth.

Placenta Structure and Function

The placenta provides nutrients to the fetus
placenta 1

So, you may remember that the placenta is the composite structure of embryonic and maternal tissues that supplies nutrients to the developing embryo. The placenta is a unique organ, found only in mammals, that allows the mother to provide a very large amount of nutrients to her offspring for an extended period of time before they are even born.

The placenta serves as an interface between the mother and the developing fetus and has three main jobs:

  1. Attach the fetus to the uterine wall
  2. Provide nutrients to the fetus
  3. Allow the fetus to transfer waste products to the mother's blood

The placenta is composed of both maternal tissue and tissue derived from the embryo. The chorion is the embryonic-derived portion of the placenta. It is composed of trophoblasts, which you may remember are the cells that made up the outer cell layer of the blastocyst. You may also remember that during implantation the trophoblasts multiply in number and extend into the uterine wall. They eventually form finger-like structures called chorionic villi, which are fingerlike structures of the placenta composed of embryo-derived trophoblasts. The chorionic villi are surrounded by maternal blood which comes into direct contact with the embryonic trophoblast cells. The intervillous space is the part of the placenta that surrounds the chorionic villi and contains maternal blood.

Blood Flow and Nutrients in the Placenta

The maternal blood contains nutrients and oxygen for the fetus
placenta 2

Maternal blood flows from the mother's circulatory system, through the intervillous space and then re-enters the mother's blood vessels. Fetal blood flows from the fetus into two main arteries in the umbilical cord, through the capillary network of the chorionic villi and is returned to the fetus by the umbilical vein. The maternal blood that enters the placenta is nutrient and oxygen rich.

A growing fetus obviously requires lots of nutrients and oxygen that it cannot provide for itself, so the fetal blood that flows through the capillaries of the chorionic villi is nutrient and oxygen poor. Because of this disparity in the nutrient and oxygen concentration between the fetal blood in the villi and the maternal blood in the intervillous space, nutrients and oxygen diffuse from the maternal blood, into the villi and into the fetal blood.

Conversely, the fetal blood contains high concentrations of carbon dioxide and other waste products, while the material blood in the intervillous space contains low concentrations of these waste products. As a result, carbon dioxide and other waste products diffuse out of the fetal blood, across the trophoblasts of the chorionic villi and into the maternal blood that surrounds the villi. The mother's lungs, kidneys and liver will easily remove these waste products from her blood. Notice that in the placenta, the maternal and fetal blood does not mix. The two blood supplies remain separated by the fetal trophoblasts and endothelial cells. However, nutrients and waste products, including oxygen and carbon dioxide, are free to diffuse from one blood supply to the other down concentration gradients.

Trophoblast Differentiation

Embryonic trophoblasts are not incorporated into the tissues of the growing fetus, but they are still very important and versatile cells.

One job of trophoblasts is to anchor the placenta to the uterus

After the chorionic villi are established, many of these trophoblasts fuse together to form very large syncytiotrophoblasts, which are large, multinucleated trophoblasts that are formed by the fusion of several smaller cells. These syncytiotrophoblasts are a main component of the chorionic villi and are the cells that are in direct contact with the maternal blood. Syncytiotrophoblasts are also the major source of most placental hormones, including human chorionic gonadotropin, which is also known as hCG.

Yet other trophoblasts form columns of cells which serve to anchor the placenta to the uterus. These junctional trophoblasts secrete extracellular matrix proteins that help them anchor the placenta to the uterus.

To unlock this lesson you must be a Member.
Create your account

Unlock Your Education

See for yourself why 10 million people use

Become a member and start learning now.
Become a Member

Already a member? Log In

Earning College Credit

Did you know… We have over 49 college courses that prepare you to earn credit by exam that is accepted by over 2,000 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Click "next lesson" whenever you finish a lesson and quiz. Got It
You now have full access to our lessons and courses. Watch the lesson now or keep exploring. Got It
You're 25% of the way through this course! Keep going at this rate,and you'll be done before you know it.
The first step is always the hardest! Congrats on finishing your first lesson.
Way to go! If you watch at least 30 minutes of lessons each day you'll master your goals before you know it.
Congratulations on earning a badge for watching 10 videos but you've only scratched the surface. Keep it up!
You've just watched 20 videos and earned a badge for your accomplishment!
You've just earned a badge for watching 50 different lessons. Keep it up, you're making great progress!
You just watched your 100th video lesson. You have earned a badge for this achievement!
Congratulations! You just finished watching your 200th lesson and earned a badge!
Congratulations! You just finished watching your 300th lesson and earned a badge!
You are a superstar! You have earned the prestigious 500 video lessons watched badge.
Incredible. You have just entered the exclusive club and earned the 1000 videos watched badge.
You have earned a badge for watching 20 minutes of lessons.
You have earned a badge for watching 50 minutes of lessons.
You have earned a badge for watching 100 minutes of lessons.
You have earned a badge for watching 250 minutes of lessons.
You have earned a badge for watching 500 minutes of lessons.
You have earned a badge for watching 1000 minutes of lessons.