Sperm production begins at puberty and continues until death, unless an illness is preventing it. Sperm take up to 72 days to mature. Millions of sperm leave the penis during ejaculation. Sperm production takes place in the testicles. The testicles need to stay around 94 degrees. High temperatures decrease healthy sperm. After the sperm grows, it travels to the epididymis to mature for two weeks. Sperm waits in the epididymis until ejaculation during sexual intercourse. Excess sperm storage takes place in the vas deferen. A healthy sperm needs an oval head and a tail. Deformed sperm usually can’t move fast enough to make it to the egg or fertilize it. Of the millions of sperm ejaculated, only one fertilizes the egg.
A woman’s ovaries release one egg a cycle, usually a month. Two ovaries and two fallopian tubes exist. The fallopian tube collects the egg from the ovary. The egg travels through the tube. If fertilization fails, the egg dies. The uterus walls thicken with mucus and blood. The lining is lost during menstruation if fertilization doesn’t happen.
During orgasm, semen collects sperm from the epididymis and ejaculates it into the vagina at a speed of 10 miles and hour. The sperm swim through the cervix, through the uterus to get to the egg. The egg waits in the fallopian tube. Mucus in the cervix and acid levels can kill sperm. Sperm last around 72 hours, once reaching the fallopian tube. The mature egg, however, only lives for a day. Some go the wrong direction on the way to the fallopian tube. Some may go to the other fallopian tube. A shell surrounds the egg, which the sperm have to break through to fertilize. After fertilization, no other sperm can enter the egg. Within 24 hours, the egg and the sperm swap chromosomes and start the growth of a baby. The fertilized egg then travels down the fallopian tube. Once the egg attaches to the wall of the uterus, the woman is pregnant.