The most profound changes that occur and markedly differentiate the two sexes are a result of the activity of the sex. In boys, the main sex hormone is testosterone. This is secreted by a boy’s sex glands, the testes. Sex hormone secretion begins at puberty and marks the start of the journey towards sexual maturity. Leydig within the testes produce testosterone under the stimulus of gonadotropins formed in the pituitary gland. This hormone, along with the gonadotropins, stimulates the production of sperm within the testes. The increase in the level of testosterone stimulates the growth of muscle and the increase in height, as well as the development of hair on the face, the trunk and the pubic region. It also triggers and maintains sexual arousal, and stimulates growth of the penis, scrotum and prostate gland. Enlargement of the penis and testes is usually the first sign that puberty has been reached. Initially the growth is slow, but at the age of 13 years or so it becomes more rapid and pubic hair appears.
The growth of the penis usually follows the increase in size of the testicles and scrotum. The ability to ejaculate seminal fluid normally begins a year after the penis starts to lengthen.
Discomfort or, if the penis is erect, extreme pain. Occasionally, phimosis may cause recurrent infection of the glans, called balanitis, because the tightness of the foreskin makes it difficult to clean the glans. Treatment usually involves circumcision, a minor operation performed under general anaesthetic, in which the foreskin is cut away from the glans penis. Before the operation it is important not to use force to pull back the foreskin because themay be damaged.