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Why So Many Sperm?

Have you ever wondered why there is such a huge disparity between the number of egg produced by women and the number of sperm produced by men? Quite simply, it is because a single sperm cannot do the job they were intended for without a lot of help.

sperm-egg

Sperm - Egg

While only a single sperm will actually make its way into the woman’s egg, it takes a sizeable number of them to break down the cumulous cells that surround the egg. The head of each sperm contains enzymes that help to dissolve the outer membrane of the egg, but once an opening appears, only one sperm will actually make it through. Once a sperm has penetrated the next level, the zona pellucida, the outer layer of the egg undergoes rapid changes which prevent any additional sperm from getting through.

Basic physics also plays a role in the need for large numbers of sperm. The trip for sperm is an uphill swim, while the course of an egg is a much easier downward drift from the ovary to the fallopian tube. Generally, a man ejaculates about 4-5ml of semen containing 100-300 million sperm, out of which only 100,000 make their way through the cervix. And finally, just 200 survive to get into the fallopian tubes.

Another drawback for sperm is that a number of them are abnormal upon creation. Some are created with two tails, no tails, misshapen tails and abnormally sized heads. Abnormal tails can make it difficult to navigate but abnormal heads mostly indicate chromosomal abnormalities.

For a sperm sample to be considered normal, only about half of them (50%) need to exhibit good mobility, so it becomes clear that many of them are not expected to make the grade. As is often the case in nature, survival of the fittest will generally prevail and mass quantities of any organism will generally produce only a handful of survivors. This is why such large quantities of sperm are needed in comparison to a single egg.

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