ENDOGENOUS ANDROGENS, INCLUDING TESTOSTERONE AND DIHYDROTESTOSTERONE (DHT) ARE RESPONSIBLE FOR THE NORMAL GROWTH AND DEVELOPMENT OF THE MALE SEX ORGANS AND FOR MAINTENANCE OF SECONDARY SEX CHARACTERISTICS. THESE EFFECTS INCLUDE THE GROWTH AND MATURATION OF PROSTATE, SEMINAL VESICLES, PENIS, AND SCROTUM; THE DEVELOPMENT OF MALE HAIR DISTRIBUTION, SUCH AS FACIAL, PUBIC, CHEST, AND AXILLARY HAIR; LARYNGEAL ENLARGEMENT, VOCAL CORD THICKENING, AND ALTERATIONS IN BODY MUSCULATURE AND FAT DISTRIBUTION.
MALE HYPOGONADISM, A CLINICAL SYNDROME RESULTING FROM INSUFFICIENT SECRETION OF TESTOSTERONE, HAS TWO MAIN ETIOLOGIES. PRIMARY HYPOGONADISM IS CAUSED BY DEFECTS OF THE GONADS, SUCH AS KLINEFELTER'S SYNDROME OR LEYDIG CELL APLASIA, WHEREAS SECONDARY HYPOGONADISM IS THE FAILURE OF THE HYPOTHALAMUS (OR PITUITARY) TO PRODUCE SUFFICIENT GONADOTROPINS (FSH, LH).