From Encyclopedia of Sex and Sexuality
The reproductive hormones are classified into three major categories: progestins, estrogens, and androgens. These three types of hormones are found in both males and females, but the amount of each is determined by the individual’s sex. The progestins and estrogens are female hormones, and the androgens are male hormones. The androgen produced in the highest concentration in the male is testosterone.
Testosterone has a complex role in the determination of secondary sexual characteristics. At puberty, testosterone production begins and affects growth, bone structure, and muscle size and tone. The male pattern of hair distribution of the body and the face are also determined by testosterone and its affects the distribution of hair on the head as the man ages.
Testosterone also affects libido and to, some extent, sexuality. Its effect on the brain accounts for some male-associated behavior characteristics, such as aggression, FSH (follicle stimulating hormone), produced by the pituitary gland, stimulates the testes to produce sperm cells. A second pituitary hormone LH (luteinizing hormone), acts on the testes to stimulate the production of testosterone which, in turn, helps maintain the production of sperm cells. The concentration of testosterone in the male remains at a fairly constant level throughout life once past puberty.