How fast do sperm swim and how do they find the egg?

08 November 2009

Question

How fast do sperm swim? And: How do they actually track down an egg? They’re doing the equivalent of flying from Earth to the Moon, and they’re blind. And they’ve got no rocket to do it in. So how do they know where to go?”

Answer

Chris - Well the answer is about 5 mm per minute, and it's in fact, five body lengths of the sperm per second. So if you scaled them up, if those were the size of a salmon, that would be the equivalent of the salmon swimming along at 500 miles an hour, or a whale doing 15,000 miles an hour. So the sperm are pretty snappy. They get to the egg pretty fast, certainly within a day or so.How do they find it? They recognize it by two means. One is a thermal gradient. They follow temperature so they know that the body gets warmer the further in they go. So they follow the thermal gradient. And then the second is that the egg oozes out various attractive molecules, in the same way that various inflammatory things attract the immune system in. This pulls the sperm towards the egg because they follow their noses, quite literally.

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