How is Sperm Created in the Testes?

The Testes

The testes are an integral part of the male reproductive system. Testes are roughly egg-shaped and sit inside the scrotal sack. They form in the abdomen and are made from the same embryonic tissue as ovaries. The presence of testosterone and a Y chromosome determine if the tissue becomes testes or ovaries. Approximately two months before birth, the testes descend into the scrotum. The testes produce both testosterone, the primary male sex hormone, and sperm. The testes are located outside the body because they need to be cooler than the rest of the body in order to produce healthy sperm. The testes regulate their temperature by drawing away from the body in hot weather and contracting toward the body in colder conditions.

Several structures within the testes--the seminiferous tubules, sertoli cells and the epididymis--play a role in sperm production.

The seminiferous tubules provide the raw materials for sperm production. Specialized cells in the lining of the tubules, called spermatogonium, divide multiple times. The cells start as round and, with each division, slowly change shape to the characteristic "tadpole" shape. The sertoli cells provide nutrition and protect the young sperm cells until they are ready to be released. When the sperm cells are ready, the sertoli cells activate their release into the seminiferous tubules and out to the epididymis.

The epididymis is a tightly coiled tube that sits inside the scrotal sack, on top of the testes. As the young sperm move from the seminiferous tubules, they take up to two weeks to travel through the epididymis. As the sperm move through the structure they mature, gain the ability to swim and are ready to fertilize an egg. The healthy sperm then move from the epididymis to the vas deferens to wait for ejaculation. On the way, the Cowper's gland and prostate add fluids to form semen. These fluids provide nutrients and help with sperm motility, or the ability to swim.

Sperm production is a continuous process and, at any given time, the testes will contain sperm at all levels of maturity. It takes approximately 74 days for a single batch to progress from the cell division stage to the vas deferens. Health status can affect sperm production and it is possible for an illness, such as a high fever, to impair sperm production.