Physical development of boys
Testosterone, produced in the testes, circulates in the blood and triggers the start of many changes, including growth spurt, pubic hair, facial and other body hair and the increased production of oil and sweat.
Boys' body shapes will change during puberty. They develop broader shoulders and narrower hips, their Adam's apple may become more pronounced and their voice will become deeper over time, often after a period where it may be erratic or squeaky. Testosterone causes the larynx to grow larger.
Testosterone also causes the changes to reproductive organs. The penis, testes and scrotum become larger and darker. Testosterone stimulates the testes to begin the production of sperm. Sperm are ideally produced at a temperature slightly lower than normal body temperature, hence the testes are held in the scrotum which hangs outside the body. Small muscles inside the scrotum enable the testes to be brought closer to the body in cold weather and hang further away in warmer conditions. Millions of sperm are produced every day.
Boys will experience erections and ejaculations, both of which are natural and normal and initially not always under their control. Ejaculation may occur during sleep (wet dream). A single ejaculation may contain between 200-500 million sperm and the volume of approximately half to one teaspoonful, although this varies.
Boys begin production of sperm at puberty and continue to produce them, often until death. The prostate gland and seminal vesicle, which are located internally next to the bladder, produce fluids that combine with sperm as it is carried from the testes via the vas deferens (long thin tube) to the penis.
In men the urethra, which carries urine from the bladder to the outside, is the same tube that transports semen from the prostate and seminal vesicle to the outside. When a man's penis becomes hard, and ejaculation occurs, the tube from the bladder is blocked so no urine mixes with the semen.
The fluids produced by the seminal vesicle and prostate gland provide lubrication, nourishment and a favourable environment for the sperm to survive travelling from a man's urethra to the acidic environment in the woman's vagina, through the uterus and into the fallopian tubes, where it may meet and fertilise the egg. The penis shaft contains spongy tissue that, when filled with blood, causes the penis to become hard and stand out from the body.
Other changes include:
- growing stronger and greater muscle development
- acne as the skin produces more oil
- underarm hair
- perspiration
- broader shoulders
- the hair on legs and arms coarsens