When it comes to semen, only the fiercest swimmers can move past the bottlenecks of the female reproductive system, new research shows. The study could one day help to improve male fertility testing. But in the meantime, it brings us adorable shots of sperm desperately floating in a fake fallopian tube. Sorry, little boys.

With a single ejaculate, 100 million sperm can swim up the female reproductive tract – and the theory is that only solid swimmers can reach the finish line: the egg. For years, however, laboratory sperm only have to undergo simple obstacle courses. This is not really a great analog for the twists of the female reproductive tract. So there are bottlenecks that alter the flow of genital mucus, which in turn can cause the sperm to swim and steer upstream. In a new study published today in the journal Scientific advances, The scientists decided to really throw the glove.

Study author Alireza Abbaspourrad and his team at Cornell University developed a device to better mimic reality and observed how both bulls and human sperm swam away. They discovered that sperm are accumulating under the opening of the bottle neck, with the fastest swimmers at the top of the pack and the slower sperm further away. That is, the fastest wrigglers compete mainly with each other and not with the slower sperm for a clear shot in the egg.

Picture credits: Zaferani et al.Sci. Adv. 2019; 5: eaav2111

The results could eventually help to design new and improved screens for faster sperm, says Abbaspourrad The edge However, this requires more research in the clinic to confirm whether these fast sperm actually produce better embryos. For the moment, it's an interesting new way to watch sperm make an improper connection between the uterus and the fallopian tube.

John Amory, a professor and fertility expert at the University of Washington who was not involved in the study, describes the device as a "tube on a chip". For him, the results weigh a key question about the sperm, which is ultimately fertilized an egg: "Is it random or must it be the best sperm?" The results prove what fertility physicians have long thought: "Clinically, we have always suspected that it the highly motile sperm responsible for fertilization. and this paper suggests that this is the right view, "he says. "It's a very cool little model."


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