Spermatogenesis requires high intratesticular levels of testosterone, secreted from the LH-stimulated Leydig cells. The testosterone diffuses across the basement membrane of the seminiferous tubule, crosses the blood-testis barrier, and complexes with ABP. Sertoli cells, but not spermato-genic cells, contain receptors for testosterone. Sertoli cells also contain FSH receptors. However, recent studies using mice, in which the P subunit of FSH has been mutated to an inactive form, reveal that the testes are small but do produce sperm. The absolute requirement for FSH in sperm production remains unknown. From these data, it appears that testosterone may be sufficient for spermatogenesis.
The actions of FSH and testosterone at each point of sperm cell production are unknown. Upon entering meio-sis, spermatogenesis appears to depend on the availability of FSH and testosterone. In human males, FSH is thought to be required for the initiation of spermatogenesis before puberty. When adequate sperm production has been achieved, LH alone (through stimulation of testosterone production) or testosterone alone is sufficient to maintain spermatogenesis.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.