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13.68: Fetal Development and the Placenta

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How does a developing baby breath?

Or eat? From mom of course. Shown is a detailed representation of the placenta. And this is where all these interactions occur.

Placenta and Related Structures

The fetus could not grow and develop without oxygen and nutrients from the mother. Wastes from the fetus must also be removed in order for it to survive. The exchange of these substances between the mother and fetus occurs through the placenta.


The placenta is a temporary organ that begins to form from the trophoblast layer of cells shortly after implantation . (For an animation showing how the placenta forms, go to link below.) The placenta continues to develop and grow to meet the needs of the growing fetus. A fully developed placenta, like the one seen above, is made up of a large mass of blood vessels from both the mother and fetus. The maternal and fetal vessels are close together but separated by tiny spaces. This allows the mother’s and fetus’s blood to exchange substances across their capillary walls without the blood actually mixing.

The fetus is connected to the placenta through the umbilical cord , a tube that contains two arteries and a vein. Blood from the fetus enters the placenta through the umbilical arteries, exchanges gases and other substances with the mother’s blood, and travels back to the fetus through the umbilical vein.

Amniotic Sac and Fluid

Attached to the placenta is the amniotic sac , an enclosed membrane that surrounds and protects the fetus (see Figure above ). It contains amniotic fluid , which consists of water and dissolved substances. The fluid allows the fetus to move freely until it grows to fill most of the available space. The fluid also cushions the fetus and helps protect it from injury.


  • The placenta allows nutrients and wastes to be exchanged between the mother and fetus.
  • The fetus is connected to the placenta through the umbilical cord.


Use these resources to answer the questions that follow.

  1. What does the Placenta do?
  2. Describe the role of hCG?
  3. How big does the Placenta get?
  1. What is the placenta?
  2. List the four embryonic membranes? Describe the roles of the membranes.
  3. Discuss the role of the placenta.


1. Describe the role of the placenta in fetal development.

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Difficulty Level:

At Grade


Date Created:

Feb 24, 2012

Last Modified:

Sep 05, 2014
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