911
CHAPTER TWENTY-THREE
Reproductive System
vive, and such advances as beta-blocker drugs and coronary
bypass surgery have extended the lives of people with heart
disease. However, the rise of new or renewed infectious dis-
eases, such as AIDS, polio, and measles, also indicates that
we cannot yet conquer all illnesses. Although we can alter
our environment more than other species can, some forces
of nature remain beyond our control.
Table 23.11
lists the
top 10 causes of death in the United States.
PRACTICE
49
Why is it dif
cult to sort out the causes oF aging?
50
How is aging a passive process?
51
How is aging an active process?
52
Distinguish between liFe span and liFe expectancy.
The human
life span
—the length of time that a human
can theoretically live—is 120 years. Although most peo-
ple succumb to disease or injury long before that point, in
many countries the fastest growing age group is those over
age eighty. These “oldest old,” having passed the age when
cancer and cardiovascular disease typically strike, are often
quite healthy.
Life expectancy
is a realistic projection of how long an
individual will live, based on epidemiological information. In
the United States, life expectancy is 75.4 years for men and
83.2 years for women. Yet in some African nations being deci-
mated by the AIDS epidemic, life expectancy is in the thirties.
Medical advances have greatly contributed to improved
life expectancy. Antibiotics have tamed some once-lethal
infections, drugs enable many people with cancer to sur-
TABLE
23.11
|
The Ten Leading Causes of Death in the United States, 2004
Cause
% of total 2,397,615 deaths
1. Heart disease
27.2
2. Cancer
23.1
3. Stroke
6.2
4. Chronic obstructive pulmonary disease (COPD)
0.5
5. Injuries
0.4
6. Diabetes mellitus
0.3
7. Alzheimer disease
0.3
8. In±
uenza and pneumonia
0.2
9. Kidney disease
0.2
²10.² InFection²(septicemia)
0.1
Source:
U.S. National Center For Health Statistics,
Health, United States, 2007.
2. Fertilization
a. With the aid of an enzyme, a sperm cell penetrates
the zona pellucida.
b. When a sperm cell penetrates a secondary oocyte
membrane, changes in the oocyte cell membrane
and the zona pellucida prevent entry of additional
sperm.
c. Completion of meiosis II forms the second polar
body.
d. Fusion of the nuclei of a sperm and a secondary
oocyte completes fertilization.
e. The product of fertilization is a zygote with 46
chromosomes.
CHAPTER SUMMARY
23.1
INTRODUCTION (PAGE 876)
Growth refers to an increase in size; development is the
process of changing from one phase of life to another.
Development includes both prenatal (ending at birth) and
postnatal (beginning at birth) life phases.
23.2
PREGNANCY (PAGE 876)
Pregnancy is the presence of a developing offspring in the
uterus.
1. Transport of sex cells
a. Ciliary action aids movement of the secondary
oocyte into the uterine tube.
b. A sperm cell moves, by its tail lashing and
muscular contraction in the female reproductive
tract, into the uterine tube.
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