HORMONAL CONTROL OF SPERM PRODUCTION: INHIBIN
In addition to GnRH, a substance called inhibin regulates FSH. Inhibin is released from the testes and, as its concentration increases, it inhibits both the secretion of FSH from the pituitary gland and the production of GnRH in the hypothalamus. Just as LH is not secreted until the level of testosterone drops, so too FSH is not secreted until the level of inhibin drops due to a decreased sperm production. In both cases, increased levels of secretion of LH and FSH result in the increased production of sperm.
Clearly, the production of sperm is no chance matter; it depends on a delicate interplay of hormones whose overproduction or underproduction can effectively inhibit a man's capacity to reproduce. In addition to the hormonal regulation of sperm, many other factors may significantly influence spermatogenesis. For example, because the hypothalamus, the gland that produces GnRH, seems to be controlled directly by the brain, some scientists speculate that stress and the psychological factors related to it can negatively affect sperm production.
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