866
UNIT SIX
After a vasectomy, sperm cells cannot leave the
epididymis, thus they are excluded from the semen.
However, sperm cells may already be present in the ducts
distal to the cuts. Consequently, the sperm count may not
reach zero for several weeks.
The corresponding procedure in the female is called
tubal ligation.
The uterine tubes are cut and tied so that
sperm cells cannot reach an egg cell.
Neither a vasectomy nor a tubal ligation changes hor-
monal concentrations or sex drives. These procedures,
shown in
f
gure 22.36
, provide the most reliable forms of
contraception. Reversing them requires microsurgery.
Table
22.5
describes several contraceptive approaches and devices
and indicates their effectiveness.
PRACTICE
64
How does an IUD prevent pregnancy?
65
Describe the surgical methods of contraception for a male and for
a female.
Intrauterine Devices
An
intrauterine device,
or
IUD,
is a small, solid object that a
physician places in the uterine cavity. An IUD interferes with
implantation of a blastocyst, perhaps by infl aming the uter-
ine tissues (F
g. 22.35
e
).
An IUD may be spontaneously expelled from the uterus
or produce abdominal pain or excessive menstrual bleeding.
It may also harm the uterus or produce other serious health
problems and should be checked regularly by a physician. A
few babies have been born with IUDs attached to them.
Surgical Methods
Surgical methods
of contraception sterilize the male or
female. In the male, a physician removes a small section of
each ductus (vas) deferens near the epididymis and ties the
cut ends of the ducts. This is a
vasectomy,
and it is an opera-
tion that produces few side effects, although it may cause
some pain for a week or two.
TABLE
22.5
|
Birth Control Methods
Method
Mechanism
Advantages
Disadvantages
Pregnancies
per Year per
100 Women*
None
85
Barrier and Spermicidal
Condom
Worn over penis or within vagina,
keeps sperm out of vagina or from
entering cervix
Protection against sexually transmitted
diseases (latex only)
Disrupts spontaneity, can
break, reduces sensation in
male
2–12
Condom and spermicide
Worn over penis or within vagina,
keeps sperm out of vagina, and
kills sperm that escape
Protection against sexually transmitted
diseases (latex only)
Disrupts spontaneity, can
break, reduces sensation in
male
2–5
Diaphragm and
spermicide
Kills sperm and blocks uterus
Inexpensive
Disrupts spontaneity, messy,
needs to be F
tted by doctor
6–18
Cervical cap and
spermicide
Kills sperm and blocks uterus
Inexpensive, can be left in 24 hours
May slip out of place, messy,
needs to be F
tted by doctor
6–18
Spermicidal F
lm, sponge,
suppository, foam, or gel
Kills sperm and blocks vagina
Inexpensive, easy to use and carry
Messy, irritates 25% of users,
male and female
3–21
Hormonal
Combination estrogen
and progestin (pill, patch,
ring, or injection)
Prevents follicle maturation,
ovulation, and implantation
Does not interrupt spontaneity, lowers
risk of some cancers, decreases menstrual
±
ow (one pill eliminates menstruation)
Raises risk of cardiovascular
disease in some women,
causes weight gain and breast
tenderness
3
Minipill
Thickens cervical mucus
Does not interrupt spontaneity
Menstrual changes
5
Medroxyprogesterone
acetate (Depo-Provera)
Prevents ovulation, alters uterine
lining
Easy to use
Menstrual changes, weight
gain
0.3
Behavioral
Rhythm method
No intercourse during fertile times
No cost
Di²
cult to do, hard to predict
timing
20
Withdrawal (coitus
interruptus)
Removal of penis from vagina
before ejaculation
No cost
Di²
cult to do
4–18
Surgical
Vasectomy
Sperm cells never reach penis
Permanent, does not interrupt spontaneity
Requires surgery
0.15
Tubal ligation
Egg cells never reach uterus
Permanent, does not interrupt
spontaneity
Requires surgery, entails some
risk of infection
0.4
Other
Intrauterine device
Prevents implantation
Does not interrupt spontaneity
Severe menstrual cramps,
increases risk of infection
3
*
The lower F
gures apply when the contraceptive device is used correctly. The higher F
gures re±
ect human error in using birth control.
previous page 896 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 898 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off