Chapter 1. Prenatal Development

Learning Objectives

conception

the fusion of the genetic material from the ovum and the sperm cell; also called fertilization

embryo

name for the developing organism from 2 weeks to 8 weeks after conception

embryonic period

prenatal development from 2 weeks to 8 weeks after conception

fetal period

prenatal development from 9 weeks to birth at about 38 weeks

fetus

name for the developing organism from 9 weeks after conception to birth

ovum

the female reproductive cell; sometimes called the egg cell

prenatal development

referring to the period of development between conception and birth

sperm cell

the male reproductive cell

viability

the point in prenatal development where the fetus could survive if born prematurely

zygote

the fertilized ovum, which now contains the full genetic material of a person

Prenatal Development

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There are five images of fetuses, one each at 9, 12, 18, 32, and 38 weeks of development. As the fetus grows the head and limbs become more defined and the fetus grows in size.

Learning Objective:

Describe the main events in the sequence of prenatal development from conception to birth.

Review

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There are 12 images of the zygote, empbryo, and fetus, starting with two cells up until 38 weeks of development. As the embryo and fetus grows the parts of the body become more defined and larger.

1. Prenatal development begins at the moment of conception: one sperm cell from the father penetrates and fertilizes the mother’s ovum, fusing the genetic material from the two cells. From this point, it takes approximately 38 weeks before the developing organism is mature enough to be born.

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image showing early development during first week after conception

2. During the first two weeks after conception, the fertilized ovum (called a zygote) doubles in size many times, and eventually attaches to the wall of the mother's uterus.

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image showing development during embryonic period

3. During the embryonic period (week 2 through week 8), all the embryo’s organ systems begin to form, and the arm and leg buds appear.

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image showing development during fetal period

4. During the fetal period (week 9 to birth at about 38 weeks), the fetus grows in size, and gradually gains viability—the capability to survive outside the womb.

Practice: Observing the Stages of Prenatal Development

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Practice: Observing the Stages of Prenatal Development

Select the PLAY button. Watch the events that occur during prenatal development, and also notice the transitions from one stage to the next.

asset/activities/prenatal/video/prenatal_anim.mp4

Quiz 1

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Quiz 1

Drag these images of early prenatal development into the correct chronological sequence. When all the images have been placed, select the CHECK ANSWER button.

Select the NEXT button and move to Quiz 2.

Perhaps you should go back to review the stages of prenatal development.

Embryo with large arm and leg buds, large head, and small tail.

Embryo with small arm and leg buds, larger torso than head, and large tail.

Fetus with large head and body, and recognizable arms and legs.

Mass of cells attaching to the uterine wall.

Quiz 2

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Quiz 2

Identify the transition point from embryo to fetus by dragging the slider to the correct point. Then, select the CHECK ANSWER button.

At this stage, it is still called a zygote. It needs to progress through the embryonic period from 2 weeks to 8 weeks before it becomes a fetus. Try moving the slider forward to about the 8 or 9 week point.

At this stage, it is still defined as an embryo because all the major organs are not yet present. Try moving the slider forward to about the 8 or 9 week point.

By 9 weeks after conception, all the major organs are in place and the risk of damage from teratogens is reduced. Select the NEXT button and move to Quiz 3.

By this stage, it has already passed the transition to a fetus. Try moving the slider back to about the 8 or 9 week point.

By the beginning of the fetal period, all the organ systems are present in rudimentary form.

asset/activities/prenatal/video/prenatal_anim.mp4

Quiz 3

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Quiz 3

Identify the approximate time of viability by dragging the slider to the correct point. Then, select the CHECK ANSWER button.

At this stage, it has not yet become viable. Try moving the slider forward to about the 22 to 25 week point.

Between about 22 and 25 weeks (during the sixth month after conception), the fetus becomes capable of living outside the womb. Select the NEXT button and move to the Conclusion.

By this stage, it has already passed the time at which it became viable. Try moving the slider back to about the 22 to 25 week point.

At a particular time in prenatal development, the developing organism becomes viable. That means it stands a chance of surviving if born prematurely at that time.

asset/activities/prenatal/video/prenatal_anim.mp4

Conclusion

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Congratulations!

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