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# 13.68: Fetal Development and the Placenta

Difficulty Level: At Grade Created by: CK-12
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Practice 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.

#### 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.

### Summary

• 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.

### Practice

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?
• http://www.hippocampus.org/Biology $\rightarrow$ Biology for AP* $\rightarrow$ Search: Human Development
1. What is the placenta?
2. List the four embryonic membranes? Describe the roles of the membranes.
3. Discuss the role of the placenta.

### Review

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

### Vocabulary Language: English Spanish

amniotic fluid

amniotic fluid

Fluid that allows the fetus to move freely; cushions the fetus and helps protect it from injury.
amniotic sac

amniotic sac

Enclosed membrane containing amniotic fluid that surrounds and protects a fetus.
implantation

implantation

Process in which a blastocyst embeds in the endometrium lining the uterus.
placenta

placenta

Temporary organ that consists of a large mass of maternal and fetal blood vessels; organ where the the mother’s and fetus’s blood exchange substances.
trophoblast

trophoblast

The outer cell layer of the blastocyst; develop into structures needed to support and nourish the embryo.
umbilical cord

umbilical cord

A tube that connects the fetus to the placenta; contains two arteries and a vein.

Feb 24, 2012

Jan 25, 2015