Psychology2016

Development across the Life Span 319

THINKING CRITICALLY

The time is coming when choosing the genetic traits of your child is going to be possible. What kinds
of ethical and practical problems may arise from this development?

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Three Stages of Development

8.5 Describe the three stages of prenatal development.

As you might imagine, the 9 months of a typical pregnancy involve a great many
changes. While many people think in terms of trimesters (3-month periods), there are
really three stages of pregnancy during which major aspects of development occur: the
germinal period, the embryonic period, and the fetal period.

THE GERMINAL PERIOD Once fertilization has taken place, the zygote begins divid-
ing and moving down to the uterus, the muscular organ that will contain and protect
the developing organism. This process takes about a week, followed by about a week
during which the mass of cells, now forming a hollow ball, firmly attaches itself to the
wall of the uterus. This 2-week period is called the germinal period of pregnancy.
The placenta also begins to form during this period. The placenta is a specialized organ
that provides nourishment and filters away the developing baby’s waste products.
The umbilical cord also begins to develop at this time, connecting the organism to the
placenta.

How does a mass of cells become a baby, with eyes, nose, hands,

feet, and so on? How do all those different things come from the

same original single cell?

During the germinal period, the cells begin to differentiate, or develop into spe-
cialized cells, in preparation for becoming all the various kinds of cells that make up the
human body—skin cells, heart cells, and so on. Perhaps the most important of these cells
are the stem cells, which stay in a somewhat immature state until needed to produce more
cells. Researchers are looking into ways to use stem cells found in the umbilical cord to
grow new organs and tissues for transplant or to repair neurological damage (Chen &
Ende, 2000; Ding et al., 2015; Holden & Vogel, 2002; Lu & Ende, 1997). to
Learning Objective 2.4.

germinal period

first  weeMs after fertili\ation

during which the \ygote moves down

to the uterus and Degins to imRlant in

the lining.

The three periods of pregnancy are the germinal period, lasting about 2 weeks, the embryonic period, from
about 2 to 8 weeks, and the fetal period, which lasts from 8 weeks until the end of pregnancy.

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