HUMAN BIOLOGY

reprodUCtIVe systeMs 317

What are the most effective methods for

preventing conception?

• The most effective methods for preventing conception are
  abstinence, surgery or implants that block the vas deferens or
  oviducts, and chemical barriers to conception such as birth
  control pills and patches.

taKe-hoMe Message

abortion The removal or

separation of an embryo or

fetus from the womb.

half of unplanned pregnancies end in induced abortion.

The difficult legal and ethical conflict over legalized abor-

tion rages on.

During the first trimester (12 weeks), abortions per-

formed in a clinical setting usually are fast, painless, and

free of complications. Even so, polls show that for both

medical and moral reasons, most people in the United

States prefer sexually responsible behavior over abortion.

Aborting a late-term fetus is quite controversial unless the

mother’s life is threatened.

This science textbook can’t offer any “right” answers

to questions about the morality of abortion or any other

reproductive decision. It can only offer an explanation

of how a new individual develops

to help you objectively assess the

biological basis of human life. We

discuss development in Chapter 17.

a spermicide. Latex condoms help prevent the spread of
sexually transmitted diseases.
A birth control pill, with its synthetic estrogens and pro-
gesterone-like hormones, blocks the maturation and ovu-
lation of oocytes. Oral contraceptives are one of the most
common methods of contraception (Figure 16.13). Some
users experience side effects, including nausea and weight
gain, although these are usually temporary. Contin ued use
may lead to blood clots in at-risk women. Complications
are more likely in women who smoke, and most physicians
won’t prescribe an oral contraceptive for a smoker.
A birth control patch is a small, flat, adhesive patch
applied to the skin. It delivers the same hormones as a birth
control pill and blocks ovulation the same way. It also has
the same risks as oral contraceptives.
Progestin injections or implants prevent ovulation or
implantation of an embryo. They may cause heavier men-
strual periods, and implants can be difficult to remove.
Even so, implants are convenient and have become increas-
ing popular, especially among younger women.
Some women use emergency contraception after a condom
tears, or after unprotected consensual sex or rape. These
“morning-after pills” suppress ovulation and in most places
are available without a prescription to women 18 and older.
They work best taken right away but may be effective up to
5 days after intercourse.

Abortion is highly controversial

An induced or surgical abortion removes or dislodges an
embryo or fetus from the womb. In the United States about

Figure 16.12 Both men and women may opt for surgical
methods of birth control. A Vasectomy and B tubal ligation.
(© Cengage Learning)

ovary

severed

oviduct

severed sections of

vas deferens

testis

A

B

Figure 16.13 Birth control pills and condoms are among the

most common methods for preventing pregnancy.

© Lusoimages/Shutterstock.com

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