Essentials of Anatomy and Physiology

Each testis is about 1.5 inches long by 1 inch wide
(4 cm by 2.5 cm) and is divided internally into lobes
(Fig. 20–4). Each lobe contains several seminiferous
tubules, in which spermatogenesis takes place.
Among the spermatogonia of the seminiferous tubules
are sustentacular(Sertoli) cells, which produce the
hormone inhibinwhen stimulated by testosterone.
Between the loops of the seminiferous tubules are
interstitial cells, which produce testosteronewhen
stimulated by luteinizing hormone (LH) from the
anterior pituitary gland. Besides its role in the matu-
ration of sperm, testosterone is also responsible for the
male secondary sex characteristics, which begin to
develop at puberty (Table 20–1).
A sperm cell consists of several parts, which are
shown in Fig. 20–1. The head contains the 23 chro-

mosomes. On the tip of the head is the acrosome,

which is similar to a lysosome and contains enzymes to

digest the membrane of an egg cell. Within the mid-

dle piece are mitochondria that produce ATP. The fla-

gellumprovides motility, the capability of the sperm

cell to move. It is the beating of the flagellum that

requires energy from ATP.

Sperm from the seminiferous tubules enter a tubu-

lar network called the rete testis, then enter the epi-

didymis, the first of the reproductive ducts.

EPIDIDYMIS

The epididymis(plural: epididymides) is a tube about

20 feet (6 m) long that is coiled on the posterior sur-

face of each testis (see Fig. 20–4). Within the epi-

The Reproductive Systems 459

Symphysis pubis

Sacrum

Ductus deferens

Urinary bladder

Corpus cavernosum

Corpus spongiosum

Cavernous urethra

Glans penis

Prepuce

Scrotum

Testis

Epididymis

Membranous urethra

Anus

Opening of ureter

Rectum

Seminal vesicle

Ejaculatory duct

Prostate gland

Bulbourethral gland

Figure 20–3. Male reproductive system shown in a midsagittal section through the

pelvic cavity.

QUESTION:Name the duct that carries sperm into the pelvic cavity.