Biology 12

Chapter 6 The Endocrine System • MHR 193

week until death. Figure 6.23 shows the major
parts of the male reproductive system.
The testes and the penis are outside the body
cavity. The testes produce the sperm and
reproductive hormones, and the penis transfers the
sperm into the female reproductive system during
sexual intercourse. The testes hang outside the
body cavity within the scrotum so that they have
the cooler temperatures (by two or three degrees)
required for the formation of healthy sperm. The
testes actually develop inside the body but descend
into the scrotum during the last two months of fetal
development. If the testes fail to descend, the result
is usually sterility. This occurs in about three
percent of all male births, but this condition can
be corrected surgically.
The testes are composed of long, coiled tubes
called the seminiferous tubules, which are
surrounded by the interstitial cells. As shown
in Figure 6.24 on the following page, the formation
of sperm (spermatogenesis) occurs within the
seminiferous tubules, which can be up to 250 m
long. The lining of each of these tubules is
composed of cells undergoing cell division

(meiosis), with sperm being continuously produced

and released from the inner lining. Sertoli cells,

which support, regulate, and nourish the developing

sperm, are also found within the tubules. As sperm

are formed, they move to the epididymisfor

maturation, where they become motile.

During sexual arousal, blood flows into the

penis and is prevented from leaving; this forms an

erection. The sperm move out of the epididymis

and the vas deferens and are mixed with fluid from

a series of glands. The seminal vesiclesproduce a

mucus-like fluid containing the sugar fructose,

which provides energy for the sperm. The prostate

glandand the Cowper’s glandsecrete an alkaline

fluid to neutralize the acids in the female

reproductive tract. This combination of sperm and

fluid enters the urethra from the urinary bladder

and exits the body. The movement of the semen,

which includes the sperm and the fluid from the

glands, is the result of a series of interactions

between the sympathetic, parasympathetic, and

somatic nervous systems. Sensory stimulation,

arousal, and the co-ordinated muscular contractions

combine to trigger the ejaculation of sperm.

urinary bladder

vas deferens

pubic symphysis

urethra

penis

glans penis

foreskin

scrotum

ureter

seminal vesicle

ejaculatory duct

prostate gland

bulbourethral gland

anus

vas deferens

epididymis

testis

Figure 6.23The testes produce sperm. The seminal vesicles, the prostate gland,
and the bulbourethral gland provide a fluid medium. Circumcision is the removal of
the foreskin. Notice that the penis in this drawing is not circumcised because the
foreskin is present.