The Reproductive System 457
Spermatids SpermatocyteBasement (^)
membrane (^)
Efferent (^) Seminiferous Mature
ductules^ Rete tubule^ spermatozoa^
Epididymis testis Septa^
Straight
tubules^
Tunica
albuginea
Sertoli^
(B) Spermatogonia cells
Ductus Lobules with coiled
(A) deferens seminiferous tubules
Figure 19- 2 The anatomy of a testis.
(^) ®
Learning
Cengage ©
Found among the developing sperm cells in the
seminiferous tubules are the Sertoli (Sir-TOH-lee) cells.
They produce secretions that supply nutrients for the
developing sperm cells, or spermatozoa (spur-mat-oh-
ZOH-ah). In the lobules of the testes, between the
seminiferous tubules in the soft connective tissue are
clusters of interstitial (in-ter-STISH-al) cells of Leydig
(SELZ of LYE-dig). The interstitial cells of Leydig
produce the male sex hormone testosterone. Thus, we see
that two different areas of the testes produce two different
products through two different groups of cells. The primary
spermatocytes in the seminiferous tubules produce sperm,
and the interstitial cells of Leydig in the tissue of the
lobules around the tubules produce testosterone. Because
the testes produce both sperm and testosterone, they are
both exocrine (glands with ducts) and endocrine (without
ducts) glands.
The Anatomy of the Spermatozoa
The spermatozoa, or mature sperm cells, are produced at a
rate of about 300 million per day. Once ejaculated, they
have a life expectancy of about 48 hours in the female
reproductive tract. They will not survive very long at all
outside the female reproductive tract in the external
environment. They are highly adapted for reaching and
penetrating a female egg or ovum. Each sperm is composed
of a head, a middle piece, and a tail (Figure 19 - 4).
The head, which developed from the nucleus of a
spermatid cell, contains the genetic material and an
acrosome (ak-roh-SOHM). The acrosome contains
enzymes that aid the sperm cell in penetrating the covering
of the female egg cell or ovum. The rest of the sperm cell
develops from the cytoplasm of the spermatid cell. The
middle piece or collar contains numerous mitochondria,
which produce the high-energy molecule adenosine
triphosphate (ATP) that provides the energy for
locomotion. The tail of the sperm cell is a typical flagellum.
The flagellum beats, from the energy of the ATP molecule,
and propels the sperm as it swims its way up the female
reproductive tract in search of an ovum.
The Functions of Testosterone
Testosterone (tess-TOSS-ter-ohn) has a number of
effects on the male body. It controls the development,
growth, and maintenance of the male sex organs. Just
before birth, it causes the descent of the testes from the
abdominal cavity into the scrotal sac. During puberty, it
stimulates bone growth, resulting in the development of
broad shoulders and narrow hips. It stimulates protein
buildup in muscles, producing muscular development,