Did you know that men make sperm every day? In contrast, a woman is born with all the eggs she will have in her lifetime. It takes approximately 75 days for one sperm to complete its growth and development. Sperm will travel from the testes where they are made, through the ejaculatory ducts where secretions are added to give them energy and also act as a barrier to the acidic environment they encounter in the vagina.
After ejaculation, sperm can survive in the female reproductive tract for up to 5 days, but is it hard work for them to reach the egg. Not only is the vagina acidic, but mucous produced by the cervix slows the progress of many, and only 1% of ejaculated sperm will succeed in reaching the uterus.
Once inside the uterus, the sperm have an easier time as contractions of the uterine muscle assist in transporting the sperm to the tubes. Here, the cells that line the tubes create waves that propel the sperm towards the egg. It is in the tube that two processes (called capacitation and hyperactivation) occur, which change the structure and function of the sperm, preparing it to meet the egg and allowing for fertilization.
Few sperm complete this arduous journey and the thick layer of cells around the egg make fertilization difficult for all but the healthiest sperm. This is truly survival of the fittest – there can be only one!