Essentials of Anatomy and Physiology

didymis the sperm complete their maturation, and
their flagella become functional. Smooth muscle in
the wall of the epididymis propels the sperm into the
ductus deferens.

DUCTUS DEFERENS

Also called the vas deferens, the ductus deferens
extends from the epididymis in the scrotum on its own
side into the abdominal cavity through the inguinal
canal. This canal is an opening in the abdominal wall
for the spermatic cord, a connective tissue sheath
that contains the ductus deferens, testicular blood
vessels, and nerves. Because the inguinal canal is an
opening in a muscular wall, it is a natural “weak spot,”
and it is the most common site of hernia formation in
men.
Once inside the abdominal cavity, the ductus defer-
ens extends upward over the urinary bladder, then
down the posterior side to join the ejaculatory duct on
its own side (see Fig. 20–3). The smooth muscle layer
of the ductus deferens contracts in waves of peristalsis
as part of ejaculation (see Box 20–2: Contraception).

EJACULATORY DUCTS

Each of the two ejaculatory ductsreceives sperm

from the ductus deferens and the secretion of the sem-

inal vesicle on its own side. Both ejaculatory ducts

empty into the single urethra (see Fig. 20–3).

SEMINAL VESICLES

The paired seminal vesiclesare posterior to the uri-

nary bladder (see Fig. 20–3). Their secretion contains

fructose to provide an energy source for sperm and is

alkaline to enhance sperm motility. The duct of each

seminal vesicle joins the ductus deferens on that side

to form the ejaculatory duct.

PROSTATE GLAND

A muscular gland just below the urinary bladder, the

prostate glandis about 1.2 inches high by 1.6 inches

wide by 0.8 inch deep (3 cm by 4 cm by 2 cm, about the

size of a walnut). It surrounds the first inch of the ure-

thra as it emerges from the bladder (see Fig. 20–3).

The glandular tissue of the prostate secretes an alkaline

The Reproductive Systems 461

BOX20–2 CONTRACEPTION

Some women report side effects such as headaches,

weight gain, and nausea. Women who use this

method of contraception should not smoke, be-

cause smoking seems to be associated with abnor-

mal clotting and a greater risk of heart attack or

stroke.

Barrier methods—These include the condom,

diaphragm, and cervical cap, which prevent sperm

from reaching the uterus and fallopian tubes. The

use of a spermicide (sperm-killing chemical)

increases the effectiveness of these methods. A con-

dom is a latex or rubber sheath that covers the

penis and collects and contains ejaculated semen.

Leakage is possible, however, and the condom is

considered 80% to 90% effective. This is the only

contraceptive method that decreases the spread of

sexually transmitted diseases.

The diaphragm and cervical cap are plastic struc-

tures that are inserted into the vagina to cover the

cervix. They are about 80% effective. These meth-

ods should not be used, however, by women with

vaginal infections or abnormal Pap smears or by

those who have had toxic shock syndrome.

There are several methods of contraception, or

birth control; some are more effective than others.

Sterilization—Sterilization in men involves a

relatively simple procedure called a vasectomy.

The ductus (vas) deferens is accessible in the scro-

tum, in which a small incision is made on either

side. The ductus is then sutured and cut. Although

sperm are still produced in the testes, they cannot

pass the break in the ductus, and they simply die

and are reabsorbed.

Sterilization in women is usually accomplished

bytubal ligation, the suturing and severing of the

fallopian tubes. Usually this can be done by way of

a small incision in the abdominal wall. Ova cannot

pass the break in the tube, nor can sperm pass from

the uterine side to fertilize an ovum.

When done properly, these forms of surgical ster-

ilization are virtually 100% effective.

Oral contraceptives(“the pill”)—Birth con-

trol pills contain progesterone and estrogen in vary-

ing proportions. They prevent ovulation by

inhibiting the secretion of FSH and LH from the

anterior pituitary gland. When taken according to

schedule, birth control pills are about 98% effective.