Infertility Frequently Asked Questions
Understanding Male Fertility
For a man, fertility means the ability to make a normally fertile woman pregnant. To do this, the man's reproductive system has to be able to produce and store sperm, and to transport the sperm outside of his body so it can enter the woman's reproductive tract.
The organs that produce sperm are called the testes. Normally a man has two testes, located in the scrotum. Each one is called a testis, also known as a testicle. Inside each testis are many tiny organs called the seminiferous tubules, which is where sperm develop.
Unlike a woman, who is born with all the eggs she will have in her life, a man makes new sperm continually. Once a man passes through puberty, his stock of sperm is refreshed about every 72 days.
The testes do their work in response to a sequence of hormonal messages in the body. Hormones are chemicals that signal the body's organs to do particular jobs. The testes produce one type of hormone, called testosterone. Other hormones involved in male fertility come from two glands in the brain, the hypothalamus and the pituitary. The hypothalamus produces gonadotropin-releasing hormone (GnRH). This prompts the pituitary to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These, in turn, stimulate the testes to manufacture sperm and to produce testosterone.
When the sperm start out in the seminiferous tubules, they are not yet mature, and they cannot move on their own. As the sperm mature, they leave the tubules and enter the epididymis, which is a coiled, tubular organ attached to the testes. Here the mature sperm learn to "swim." Mature sperm resemble tadpoles, with an enzyme-coated head and a tail.
To get out of the man's body, the sperm must travel from the epididymis through a series of tubes, including the vas deferens and the ejaculatory duct. As it moves through this path, the sperm combines with secretions from the epididymis, the vas deferens, the seminal vesicles, and the prostate. The resulting fluid is called semen. When the man has an orgasm, this fluid moves into the urethra (the tube that runs down the length of the penis) and comes out of the penis, carrying the sperm with it. This process is called ejaculation.
During intercourse, the man's ejaculation carries the sperm into his partner's vagina. The sperm must then make their way through the woman's cervix (the entrance to the uterus) into her uterus, and from there into the fallopian tubes. If an egg is passing through the fallopian tubes at this time, one of the sperm can enter the egg, fertilizing it and starting a pregnancy. If a man does not ejaculate his sperm, they die and are reabsorbed by the body.