[FONT=Times New Roman, Times, serif] Men's [/FONT][FONT=Arial,Helvetica,sans-serif] glands do not secrete enough testosterone, the result is a lower concentration of serum testosterone in the bloodstream. Testosterone levels fall below the bottom of the 'normal' range so that homeostasis breaks down and the body no longer functions as well as it could. The cells whose receptors react to testosterone do not perform their functions as well and the man begins to show symptoms of hypogonadism: Men the older they get the lower the Testosterone levels become.
Physiological issues and injuries are other causes as well.
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