838
UNIT SIX
The inner lining of the epididymis is composed of pseu-
dostratiF
ed columnar cells that bear nonmotile cilia. These
cells secrete glycogen and other substances that support
stored sperm cells and promote their maturation.
When immature sperm cells reach the epididymis,
they are nonmotile. However, as they travel through the
epididymis as a result of rhythmic peristaltic contrac-
tions, they mature. ±ollowing this aging process, the sperm
cells can move independently and fertilize egg cells (ova).
However, they usually do not “swim” until after ejaculation.
the two seminal vesicles, prostate gland, and two bulboure-
thral glands.
Epididymides
The
epididymides
(ep
ı˘-di-dy
mides; sing.,
epididymis
) are
tightly coiled, threadlike tubes about 6 meters long (see
f
gs.
22.4,
22.12
, and reference plate 12). Each epididymis is con-
nected to ducts in a testis. It emerges from the top of the
testis, descends along its posterior surface, and then courses
upward to become the ductus deferens.
Spermatozoa (Sperm
cells, 23 chromosomes,
1 chromatid per
chromosome)
Changes in
chromosome
structure
Sustentacular cells
Spermatid
(23 chromosomes, 1
chromatid per chromosome)
Nucleus of
sustentacular cell
Secondary spermatocyte
(23 chromosomes, 2
chromatids per chromosome)
Meiosis I
Spermatogonium
mitosis
Primary spermatocyte
(46 chromosomes, 2
chromatids per chromosome)
Tight junction
between sustentacular
cells (blood-testis barrier)
Daughter cell in late
interphase (Type B
spermatogonium,
46 chromosomes 2
chromatids per chromosome)
Daughter cell in late
interphase (New type
A spermatogonium,
46 chromosomes 2
chromatids per chromosome)
Basement
membrane
Developmental sequence
Wall of seminiferous
tubule
Lumen of seminiferous
tubule
Meiosis II
FIGURE 22.9
Spermatogonia (type B) give rise to primary spermatocytes by mitosis; the spermatocytes, in turn, give rise to sperm cells by meiosis.
Type A spermatogonia continue the germ cell line.
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