Sperm are highly adept at swimming against a current, new research shows. This revelation could lead to more efficient artificial insemination techniques, according to the researchers.
The discovery, made by researchers at Massachusetts Institute of Technology (MIT) and Cambridge University, was published in the journal eLife.
This may help us to better understand how some sperm travel such long distances through difficult terrain to reach and fertilize an egg.
While we know that sperm cells can "smell" chemicals given off by the egg once they get very close to it, this does not explain how they navigate for the majority of their journey, Jörn Dunkel, an assistant professor of mathematics at MIT, and research team member told ScienceDaily.com.
“We wanted to know which physical mechanisms could be responsible for navigation,” Dunkel said in an MIT press release. “If you think of salmon, for example, they can swim against the stream, and the question was whether something similar could really be confirmed for human sperm cells.
It is an extremely difficult journey. Hundreds of millions of sperm start out but only a very few reach the egg. They have to travel long distances -- up to 1,000 times their length -- while being exposed to different chemicals and currents along the way.
Since watching sperm swimming in the human body is too difficult, Dunkel and colleagues conducted lab experiments in which they changed the flow of fluid in specially designed tubes, to observe how sperm responded to different current speeds.
Researchers found that at certain current speeds, sperm are able to very efficiently swim upstream. In addition, instead of swimming upstream in a straight line, sperm swim in a spiral motion near the walls of the tube, where the current flow would likely be slower.
Next, the researchers want to learn whether or not sperm work together to reach an egg.
"It is a commonly held belief that there is competition between sperm cells, with the fittest reaching the egg first," Dunkel said to HealthDay News.