Puberty

Major pubertal hormones secreted by the hypothalamus include gonadotropin releasing hormone (GRH) and growth hormone releasing hormone (GHRH). Both target the anterior pituitary gland, which in turn releases gonadotropins and growth hormone (also known as somatotropin). GRH is released in a pulsative fashion. This pulsation triggers release of the gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH). LH stimulates testosterone release by the testes, and FSH is required for early stages of sperm maturation. GHRH is released on a daily basis throughout life, but growth hormones have an enhanced effect during puberty when they are combined with sex hormones.

The age of onset of puberty varies but can be between the ages of 9 and 14 in boys. However, individuals can mature as late as 20. When all of a male's organs and endocrine functions are normal but testicular development never occurs, he is said to display eunuchoidism. This name originates from China where servile classes of eunuchs were created by removing their testicles. Because of their lack of testosterone, they were less aggressive. Puberty that begins before the age of eight is called precocious. Precocious puberty can result from neurological disorders of the posterior hypothalamus or pituitary disorders such as tumors or infections.

The initial sign of male puberty is testicular enlargement. The testes secrete testosterone, which stimulates many primary and secondary sexual characteristics. Testosterone causes the prostate gland and seminal vesicles to mature. The seminal vesicles begin to secrete fructose which is the primary nutrient sperm require. During puberty, primitive male germ cells begin to mature into primary spermatocytes. This early step in sperm maturation is testosterone-independent. However, the final stage of sperm maturation into spermatozoa is testosterone-dependent. Testicular size may double or quadruple at the start of puberty, but the rate of testicular growth is greatest in the middle of puberty. By the end, they will have doubled in size again. There is great variability in the final testicular size from man to man, but this difference has no affect on sexual ability.

The general progression of male genital area development is the onset of testicular enlargement, onset of penile enlargement, and the appearance of pubic hair (pubarche). The scrotal skin also becomes darker and more wrinkled. Penile enlargement usually begins about a year after testicular growth begins. The penis first becomes longer, and then becomes broader. Initial ejaculations usually occur later during sleep. Sperm count is low, at first.

Facial hair growth and a deepening voice are two secondary sexual characteristics which develop about two years after pubic hair appears in males. Facial hair begins on the upper lip, becomes more confluent, extends to side-burns, and then grows on the chin. Hair also begins to appear on a pubertal boy's chest and abdomen. The voice deepens by dropping in pitch due to enlargement of the vocal cords in the larynx, voice box. In addition, other body hair grows, and the areola (pigmented ring around the nipple) enlarges.

Boys grow considerably in both height and mass during puberty. On average, boys will grow about 3.7 in/year (9.5 cm/year) at the peak year of their growth spurt. Boys average 4 ft 7 in (1.4 m) in height prior to the onset of puberty and grow an additional 15 in (38 cm) taller during their pubertal growth spurt. At the end of puberty, the average male height is 5 ft 10 in (1.8 m). The initial growth occurs in the leg bones increasing leg length. Then the torso lengthens causing an increase in sitting height. Between leg growth and torso growth, the arms, shoulders, and hips of boys grow considerably, as well. Muscle mass also increases-particularly in the shoulders. A temporary drop in subcutaneous fat occurs in the arms during this time with fat levels returning to normal at the end of puberty.