This happens when the testes are small and there are very few tubules. When this happens there could be a great deal of infertility. There may also be degeneration of the tubules, which could lead to the same outcome, infertility. Testosterone is a hormone that stimulates sperm production and controls the development of male sexual characteristics. It is LH that stimulates the release of the hormone, which is found in the testicles. It helps deepen a guy's voice, more body hair, more muscles and stronger bones. If there is a testosterone deficiency, a man may have brittle bones, decreased body hair, and decreased muscle mass. It could be caused by chronic illness, injury, age or stress. Another could be too much testosterone. This could cause a man to have fewer heart attacks, less likely to have obesity, more alcoholism and more likely to get injured. They are more risk-taking and the cause is mainly genetic. The epididymis is a tube behind the testes that allows sperm to pass into the vas deferens. It is a long tube that sits right next to the testicles. Its purpose is to transport immature sperm and allow them to mature along the way.