Blood: It's A Jungle In There : Shots - Health News This scanning electron micrograph of a blood clot — taken from the coronary artery of somebody who had a heart attack — might be scary if it weren't so cool.
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Blood: It's A Jungle In There

A really, really tight shot of a blood clot. Courtesy Andre E.X. Brown, Rustem I. Litvinov, Dennis E. Discher, Prashant K. Purohit, John W. Weisel, University of Pennsylvania/Science hide caption

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Courtesy Andre E.X. Brown, Rustem I. Litvinov, Dennis E. Discher, Prashant K. Purohit, John W. Weisel, University of Pennsylvania/Science

This scanning electron micrograph of a blood clot -- taken from the coronary artery of somebody who had a heart attack -- might be scary if it weren't so cool.

It's a colorized portrait from University of Pennsylvania researchers reporting in this week's Science. Their study details the role a versatile molecule called fibrin plays in sealing off a wound or, in the case of a heart attack, blocking a blood vessel.

Look closely: The brown mesh is a wiry web of fibrin molecules. Strengthened by the purple-grey platelets, the fibrin mesh bends and stretches without breaking to catch red blood cells and infection-fighting white blood cells (tinted green in the photo) like fish in a net. Where does that flexibility come from?

The Penn study suggests the key is the way each molecule unfolds when tugged, exposing hidden inner parts of the fibrin string that then actively expel water. "That's how the whole clot volume decreases about ten-fold with three-fold stretching," says Penn biologist John Weisel. It's this molecular unfolding, the scientists write, "that allows clots to stretch so far."