Development of the Genitals in Boys 02

By themselves, sperm are very sluggish. In fact, they hardly have the energy to move at all. Just prior to ejaculation, the sperm get this boost of energy from the semen, and start flailing their tails about, whipping around, anxious to get going. They don't have very far to travel. They only go about 15 centimetres, but to a sperm that's the equivalent of running six and a half kilometers at top speed!

During an erection, the inside of the penis fills up with blood and the muscles at the base of the penis contract and close off the vessels, making the penis swell and become hard. When one ejaculates, the prostate gland contracts and helps push the sperm and semen into the centre of the erect penis through a tube called the urethra.

The body uses the urethra tube to expel both semen and urine, but there is a tiny valve that blocks off the bladder just before ejaculation and two very small glands release a neutralizing liquid to flush out any acidic urine that may still be in the tube before the sensitive sperm travels through.

The sperm are pushed along through the urethra by the contracting of the muscles in the penis and surrounding area. The semen and sperm come out of the tip of the penis, usually in three or four spurts. The fluid is white, sticky and sort of creamy looking. After ejaculation, everything returns to normal. The penis gets soft and smaller, and the testicles relax.


  • Vas Deferens
  • Bladder
  • Pubic Bone
  • Urethra
  • Glands Penis
  • Testis
  • Scrotum
  • Epididymis
  • Prostate Gland
  • Seminal Vesicle
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