Male Reproductive System
The male reproductive system is made up of external and internal organs. The external organs of the male reproductive system are the penis and scrotum. The scrotum contains two organs called testes. As males mature sexually, the testes begin to produce testosterone, the male hormone, and sperm, which are male reproductive cells.
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Each sperm cell has a head and tail. The head contains hereditary information, and the tail moves the sperm. Sperm are produced in greater numbers at lower temperatures.Many organs help in the production, transportation, and storage of sperm. After sperm are produced, they travel from the testes through sperm ducts that circle the bladder. Behind the bladder, a gland called the seminal vesicle provides sperm with a fluid. This fluid supplies the sperm with an energy source and helps them move. This mixture of sperm and fluid is called semen. Semen leaves the body through the urethra, which is the same tube that carries urine from the body. However, semen and urine never mix.

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Although 200 million to 300 million sperm can be deposited in the vagina, only several thousand reach an egg in the oviduct. As they reach the female, the sperm come into contact with chemical secretions in the vagina. The sperm then become capable of fertilizing the egg.Once a sperm has entered the egg, changes in the eletric charge of the eggs membrane prevent other sperm from entering the egg.