Sperm Production

The sperm production process

The male reproductive cell is the sperm. From puberty, sperm production occurs continuously throughout a man's life into old age. This contrasts to the female reproductive system where the female reproductive cells (eggs) are produced in a cyclical manner, once a month, which stops later in life at menopause.

Sperm are produced in the seminiferous tubules in the testis. They start of as germ cells (precursors of sperm) and pass through many stages of change including a striking change in shape, from a round cell to the familiar 'tadpole' sperm structure. The entire process of sperm production (spermatogenesis) from germ cells to the development of a mature sperm that can fertilize an egg takes about 70 days to complete and cannot be altered. Mature sperm are highly specialised cells.

When the sperm development process is complete, sperm are released from the wall of the sperm-producing tubes (seminiferous tubules) and transported to the epididymis. When sperm leave the testes, they are not moving forward ('non-motile') and can not recognise and penetrate an egg at this stage. It is while the sperm passes through the epididymis (a process that takes 4-10 days) that they gain these abilities. These changes in the sperm are called sperm maturation and are vital for fertilisation to happen. The exact details of the changes that happen during sperm maturation in the epididymis remain a mystery. It is difficult to get samples from the epididymis to test without damaging the tube itself. When the sperm leave the epidydimis they are referred to as being mature and now able to fertilize an egg.

Sperm are stored at the end of the epididymis, in the tail, or cauda. During ejaculation, waves of muscle contractions along the reproductive tract push a small amount of sperm from the epididymis into the vas deferens. The sperm travel through the vas deferens which carries them through a twisting course through the groin to the back of the bladder. Sperm then travel through the ejaculatory duct which passes through the prostate gland into the urethra. As sperm pass through the different tubes, they are bathed in small amounts of fluid. More fluid from the seminal vesicles and prostate gland is added to the sperm. The mixture is then called semen. Over 90% of the ejaculate is produced from the prostate and seminal vesicles and not from the testis. For this reason, men who have had a vasectomy do not notice any change in ejaculation.