In men, 90% of blood testosterone comes from the testes and it reflects the function of interstitial cells. Reduced blood testosterone is mostly seen in men with Turner syndrome, mesenchymal cell dysplasia and anencephaly. Causes of lower blood testosterone The physiological properties of testosterone mainly include the following five aspects: 1. Influence embryonic development and promote the growth and development of male accessory organs. Testosterone can stimulate the growth and development of the prostate, penis, scrotum, urethral bulb gland and other accessory sex organs; 2. Stimulate the growth of reproductive organs and the appearance of paraphilias. Testosterone can stimulate and maintain male paraphilias, and can also produce and maintain normal libido; 3. Testosterone is secreted from the interstitial cells and can enter the varicocele through the basement membrane to bind with the corresponding receptors of spermatogenic cells and promote spermatogenesis; 4, affect metabolism. Testosterone can promote protein synthesis, especially protein synthesis in muscles and bones; affect water and salt metabolism, facilitating the retention of water and sodium in the body; increase the deposition of calcium and phosphorus in bone; 5. Abnormalities in physiological functions will in turn trigger abnormalities in blood testosterone concentrations. Etiology of low serum testosterone concentration Testosterone is derived from cholesterol. The male testes produce large amounts of testosterone, and the female ovaries, placenta and adrenal reticular formation in both males and females also produce small amounts of testosterone. Hypogonadism, male testicular lesions, coronary atherosclerosis, and exogenous androgen intake can all affect serum testosterone concentrations.