New 3D images of shark intestines show they work like Tesla valves

A CT scan image of a dogfish shark spiral intestine, shown from the top looking down. (Samantha Leigh/California State University, Dominguez Hills)

TORONTO — Despite sharks being frequently cast as the ‘scary creature with large teeth’ in our collective imagination, not a lot is known about what sharks actually eat and how they can go so long between meals.

But new 3D imaging may have unravelled some of those digestive mysteries by creating a better picture of what a shark’s intestines look like.

According to a new study published in the journal Proceedings of the Royal Society B, researchers have made images using CT scans that allow a closer look at the animal’s spiral intestines, which may allow it to digest food slowly.

"It's high time that some modern technology was used to look at these really amazing spiral intestines of sharks," Samantha Leigh, assistant professor at California State University and lead author of the study, said in a press release. "We developed a new method to digitally scan these tissues and now can look at the soft tissues in such great detail without having to slice into them."

Researchers took CT scans of around three dozen shark species from specimens preserved at the Natural History Museum of Los Angeles. This process involved taking a series of X-rays from different angles and then combining those flat images to produce a 3D one.

This meant researchers didn’t have to dissect a shark and disturb the organs involved.

"Intestines are so complex, with so many overlapping layers, that dissection destroys the context and connectivity of the tissue,” co-author Adam Summers, a professor based at UW Friday Harbor Labs, explained in the release.

"It would be like trying to understand what was reported in a newspaper by taking scissors to a rolled-up copy. The story just won't hang together.”

By examining these 3D images, researchers were able to theorize that the spiral shape of the sharks intestines actually help them retain food for longer. The spiral shape of the gut slows down the progress of food through the shark, moving based on gravity and the contraction of the intestines.

The release explained that the sharks’ intestines function similarly to a one-way valve designed by Nikola Tesla more than 100 years ago, in that it allows fluid to move in one direction without any backflow or external help from other moving parts.

Contrary to how often the shark in Jaws was seen chowing down, sharks often go for days or even weeks between meals, so these spiral intestines may help them stretch out one large meal, researchers say.

The next step for researchers is to create these structures themselves using a 3D printer, and see what happens when material passes through them in real time. The release also mentioned that these structures could serve as inspiration for technology and things such as wastewater treatment or filtering out microplastics from water.

As sharks eat a wide variety of things in the ocean and are frequently top predators, understanding more about how they digest could help us understand more about the ocean ecosystem in general.

“The vast majority of shark species, and the majority of their physiology, are completely unknown,” Summers said, adding that new things are discovered every time they look closely.

"We need to look harder at sharks and, in particular, we need to look harder at parts other than the jaws, and the species that don't interact with people."