Essentials of Anatomy and Physiology

tion occurs, the nuclei of the egg and sperm merge,
and the fertilized egg (zygote) has 46 chromosomes,
the diploid number. Thus, meiosis maintains the
diploid number of the human species by reducing the
number of chromosomes by half in the formation of
gametes.

MALE REPRODUCTIVE SYSTEM

The male reproductive system consists of the testes
and a series of ducts and glands. Sperm are produced
in the testes and are transported through the repro-
ductive ducts: epididymis, ductus deferens, ejaculatory
duct, and urethra (Fig. 20–3). The reproductive glands
produce secretions that become part of semen, the

fluid that is ejaculated from the urethra. These glands

are the seminal vesicles, prostate gland, and bul-

bourethral glands.

TESTES

The testesare located in the scrotum, a sac of skin

between the upper thighs. The temperature within

the scrotum is about 96F, slightly lower than body

temperature, which is necessary for the production

of viable sperm. In the male fetus, the testes develop

near the kidneys, then descend into the scrotum just

before birth. Cryptorchidism is the condition in

which the testes fail to descend, and the result is

sterility unless the testes are surgically placed in the

scrotum.

The Reproductive Systems 457

Mitosis

Spermatogonium

Stem cell

New stem cell

Figure 20–1. Spermatogene-
sis. The processes of mitosis and
meiosis are shown. For each pri-
mary spermatocyte that under-
goes meiosis, four functional
sperm cells are formed. The struc-
ture of a mature sperm cell is also
shown.
QUESTION:How many chromo-
somes does a sperm cell have,
and where are they located?