FIGURE 3. The Hypothalamo-Pituitary Testicular Axis in Health and Intrinsic and Extrinsic Diseases. Schematic representation of the hypothalamo-pituitary-testicular (HPT) system in health (left panel) and in disease (right panel). Note in the right panel the distinction between organic disorders of the reproductive system causing pathologcal hypogonadism leading to male infertility and/or androgen deficiency and, alternatively, non-reproductive disorders which lead to an adaptive hypothalamic response to systemic non-reproductive disorders. While these non-reproductive disorders may lead to a reduced serum testosterone, that is neither a testosterone deficiency state nor warrants testosterone treatment without convincing evidence of safety and efficacy.