HUMAN BIOLOGY

310 Chapter 16

the Male reproductive system

n A male’s testes produce sperm and hormones that govern

male reproductive functions and traits.

n Links to Flagella 3.9, Testosterone 15.11

Sperm form in testes

Figure 16.4 shows an adult male’s reproductive system, and

Table 16.2 lists the functions of its organs. In an embryo that

will develop as a male, two testes form on the abdominal

cavity wall. Before birth, the testes descend into the scro-

tum, a pouch of skin suspended below the pelvic girdle

(Figure 16.5). Inside this pouch, smooth muscle encloses

the testes.

For sperm to develop properly, the temperature inside

the scrotum must be a few degrees cooler than body core

temperature. To this end, a control mechanism helps assure

that the scrotum’s internal temperature is always close to

95°F. When a male feels cold (or afraid), muscle contractions

draw his testes closer to his body.

When he feels warm, the muscles

relax and allow the testes to hang

lower, so the sperm-making cells do

not overheat.

Reproductive organs

Testis (2) Sperm, sex hormone

production

Epididymis (2) Site of sperm maturation and

subsequent storage

Vas deferens (2) Rapid transport of sperm

Ejaculatory duct (2) Conduct sperm to penis

Penis Organ of sexual intercourse

Accessory glands

Seminal vesicle (2) Secrete most fluid in semen

Prostate gland Secretes some fluid in semen

Bulbourethral gland (2) Secrete lubricating mucus

Table 16.2 Male Reproductive System

anus

Epididymis

One of a pair of ducts

in which sperm finish

maturing; the portion

farthest from the testis

stores mature sperm

Vas deferens

One of a pair of ducts for

transport of sperm

Bulbourethral

gland

One of a pair of

glands that secrete

lubricating mucus

Seminal vesicle

One of a pair of glands

that secrete fructose

and prostaglandins,

which become part

of semen

Ejaculatory duct

One of a pair of sperm-

conducting ducts

One of a pair of primary male reproductive organs; packed with

sperm-producing tubules and cells that secrete testosterone, other hormones

Testis

Dual-purpose duct; serves

as channel for ejaculation of

sperm during sexual arousal;

also for urine excretion at

other times

Urethra

bladder

Prostate gland

Secretion of substances

that become part of semen

Penis

Organ of sexual

intercourse

erectile tissue

urethra

Figure 16.4 Animated! The male reproductive system includes testes and many accessory structures. (© Cengage Learning)

16.3

testes A male’s gonads;
his primary reproductive
organs.

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