Reproduction
607
Vas
deferens
Ejaculatory
duct
Urinary
bladder
Ureter
Seminal
vesicle
Prostate
gland
Bulbourethral
gland
Epididymis
Testis
Urethra
Penis
Pubic
bone
Figure 17–6
Anatomic organization of the male reproductive tract. This fi gure shows the testis, epididymis, vas deferens, ejaculatory duct, seminal vesicle,
and bulbourethral gland on only one side of the body, but they are all paired structures. The urinary bladder and a ureter are shown for
orientation but are not part of the reproductive tract. Once the ejaculatory ducts join the urethra in the prostate, the urinary and reproductive
tracts have merged.
Spermatogonia
Mitosis
Differentiation
Primary spermatocytes
Secondary spermatocytes
2nd meiotic division
1st meiotic division
Differentiation
Chromosomes
per
cell
46
46
23
23
Chromatids
per
chromosome
2
2
1
1
Spermatids
Spermatozoa
23
2
Figure 17–7
Summary of spermatogenesis, which begins at puberty. Each spermatogonium yields, by mitosis, a clone of spermatogonia; for simplicity, the
fi gure shows only two such cycles, with a third mitotic cycle generating two primary spermatocytes. The arrow from one of the spermatogonia
back to a stem cell spermatogonium denotes the fact that one cell of the clone does not go on to generate primary spermatocytes, but reverts to
an undifferentiated spermatogonium that gives rise to a new clone. Note that each primary spermatocyte produces four spermatozoa.
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