HUMAN BIOLOGY

352 Chapter 17

your Future

Dr. E. Walker/Science Source

Figure 17.25 This embryo, the

result of an ectopic pregnancy,

could not survive implantation

outside its mother’s uterus.

4. The developmental process called produces the
   shape and structure of particular body regions.


5. is the gene-guided process by which cells in
   different locations in the embryo become specialized.
   a. Implantation c. Cell differentiation
   b. Neurulation d. Morphogenesis


6. In a human zygote, the cell divisions of cleavage produce
   an embryonic stage known generally as a.
   a. zona pellucida c. blastocyst
   b. gastrula d. larva


7. Match each developmental stage with its description.
   cleavage a. egg and sperm mature
   gamete formation in parents
   organ formation b. sperm, egg nuclei fuse
   cell differentiation c. germ layers form
   gastrulation d. zygote becomes a ball of
   fertilization cells called a morula
   e. cells come to have specific
   structures and functions
   f. starts when germ layers
   split into subgroups of cells


8. Of the four extraembryonic membranes, only the is
   not needed in order for an embryo to develop properly.
   a. yolk sac d. chorion
   b. allantois e. this is a trick question,
   c. amnion because all are needed


9. All of the following apply to the birth process (labor) except
   .
   a. It consists of four main stages.
   b. Hormones from the fetus trigger it.
   c. In a newborn, breathing air triggers the shutdown of the
   “bypass” vessels of fetal circulation.
   d. It is an example of positive feedback rather than negative
   feedback.


10. Of the following, cannot cross the placenta.
    a. alcohol
    b. the mother’s antibodies
    c. antibiotics
    d. toxic substances in tobacco smoke
    e. all can cross the placenta

CritiCaL tHinKing

1. How accurate is the statement “A pregnant woman must
   do everything for two”? Give some specifics to support
   your answer.


2. A renowned developmental biologist, Lewis Wolpert, once
   observed that birth, death, and marriage are not the most
   impor tant events in human life—rather, Wolpert said, the
   most important moment in life is gastrulation. Given the
   discussion in Section 17.1, what do you think he meant?


3. One of your best friends tells you that she and her husband
   think she might be pregnant. She feels she can wait until
   she’s several months along before finding an obstetrician.
   You think she could use some medical advice sooner, and
   you suggest she discuss her plans with a physician as
   soon as possible. What kinds of health issues might you be
   concerned about? © Gary Head
   4. The complications of ectopic
   pregnancy (Section 17.2)
   are life-threatening for the
   mother, and in fact each year
   in the United States a few
   pregnant women die when
   their situation is not diagnosed
   in time. Tragically, the only
   option is to surgically remove
   the embryo, which was
   doomed from the beginning.
   Based on what you know about
   where an embryo normally
   develops, explain why the
   ectopic embryo in Figure 17.25
   could not have long survived.

Zephyr/Science Source

Researchers studying Alzheimer’s

disease may be making significant

progress in understanding how the

disease takes hold in the brain. They

already know that not everyone who

develops AD’s characteristic tangles

and plaques goes on to develop

the disease itself. Now scientists at

Harvard University have discovered that

protection may come from a brain protein called REST that

was thought to act only during fetal life, helping assure proper

timing of neural development in the brain. The Harvard team

discovered that REST becomes active again in older adults—

except in people who develop AD. As more is learned about

REST’s role in adults, researchers hope the knowledge may

lead to therapies for preventing Alzheimer’s or slowing its

progress in the brain.

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