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Review |
From the Animal Reproduction and Biotechnology Laboratory, Colorado State University, Fort Collins, Colorado.
| Correspondence to: Rupert P. Amann, 909 Centre Ave, No. 123, Fort Collins, CO 80526 (e-mail: rpalra62{at}comcast.net). |
Understanding the dynamics of spermatogenesis is central to clinical
andrology or to probing environmental effects on human testes. This review
considers what is known about renewal and proliferation of spermatogonia, how
germ cells are organized in cellular associations constituting the cycle of
the seminiferous epithelium, relative frequencies of cellular associations,
durations of the cycle of the seminiferous epithelium and spermatogenesis, and
measurement of daily sperm production. Daily sperm production (DSP) per testis
tends to decline with advancing age. Regardless of age, there is substantial
loss of potential sperm from degeneration of spermatocytes, but not
spermatids. DSP per gram testis parenchyma or DSP per testis cannot be
predicted on the basis of testis size or age of a man. The review shows why
our 1960s data base is neither robust nor precise and suggests how
deficiencies might be rectified. New cellular associations should be defined,
with none representing >15% of the cycle of the seminiferous epithelium.
Then determine when Apale-spermatogonia become committed to
proliferate or how many mitotic divisions occur thereafter. Restudy the
duration of spermatogenesis because the accepted value might be in error by
6 days. Restudying human spermatogenesis will benefit clinicians,
toxicologists, and epidemiologists probing testis function by direct
evaluations or indirectly via evaluations of quantity and quality of sperm
ejaculated. It also will benefit scientists interested in renewal and
proliferation of spermatogonia, or a spermatogonium as a prototype stem
cell.
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