HUMAN BIOLOGY

reprodUCtIVe systeMs 311

bulbourethral glands

Glands of the male repro-

ductive system that produce

mucus.

epididymis Duct where

sperm mature and are

stored.

penis The male sex organ.

prostate gland Gland

of the male reproductive

system that secretes some

substances in semen.

semen The fluid contain-

ing sperm that is expelled

from the penis during sexual

activity.

seminal vesicles Glands

that secrete most of the

fluid in semen.

vas deferens Tube that

carries sperm from an epi-

didymis to the ejaculatory

duct.

hoW do a male’s testes function in

reproduction?

• The testes are primary reproductive organs that produce sperm
  and male sex hormones.


• The male reproductive system also includes accessory glands
  and ducts.


• When sperm are nearly mature, they leave each testis and enter
  the long, coiled epididymis, where they remain until ejaculated.


• Secretions from the seminal vesicles and the prostate gland mix
  with sperm to form semen.

taKe-hoMe Message

signaling molecules that can trigger

muscle contractions. During sex, the

prostaglandins cause smooth mus-

cles of a female’s reproductive tract

to contract, and so aid the movement

of sperm through it toward the egg.

Substances secreted by the

prostate gland may help buffer

the acidic environment that sperm

encounter in the female reproductive

tract. The vaginal pH is about 3.5 to

4.0, but sperm motility improves at

pH 6. Bulbo urethral glands secrete

mucus-rich fluid into the urethra

when a male is sexually aroused.

This fluid neutralizes acids in any

traces of urine in the urethra. The

more alkaline surroundings create

a more favorable chemical envi-

ronment for the 150 to 350 million

sperm that pass through the urethra

in a typical ejaculation.

sperm mature and are stored
in the coiled epididymis

When sperm leave a testis they enter a long, coiled duct
called an epididymis (ep-i h-did-ih-muss; plural: epididy-
mides). At this point, the sperm aren’t mature. Gland cells
in the walls of the ducts secrete substances that trigger
final developmental changes. Until sperm leave the body,
they are stored in the last stretch of each epididymis.
When a male is sexually aroused, muscle contractions
propel mature sperm from each epididymis into and
through a pair of thick-walled tubes. Each tube is called
a vas deferens. From there, contractions move sperm
through the two ejaculatory ducts and on through the ure-
thra to the outside. The urethra passes through the penis,
the male sex organ, and also carries urine.

substances from seminal vesicles and
the prostate gland help form semen

Secretions from several glands mix with sperm as they travel
through the urethra. The result is semen, a thick fluid that
is eventually expelled from the penis during sexual activ-
ity. As semen begins to form, a pair of seminal vesicles
secrete fructose. The sperm use this sugar for energy. Semi-
nal vesicles also secrete certain kinds of prostaglandins.
You may recall from Chapter 15 that prostaglandins are

Figure 16.5 The male reproductive system is located in the
lower pelvic region. (© Cengage Learning)

pelvic

girdle

bladder

scrotum

Sperm cell arriving at an egg

Don W. Fawcett/Science Source

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