Shark Intestines Have Spiral Structures That Function Like Tesla Valves, New 3D Images Reveal

One of the lesser-known things about sharks is how they eat in full - from the food they eat to how they digest what they eat - and a new set of 3D images shows what they look like.

Sharks have been among the oldest species to roam the world, and scientists have relied on flat sketches to understand how a shark's digestive system works and the effect of its excretion on the environment. With a new set of high-resolution, 3D images of shark intestines taken from about three dozen shark species, researchers are looking forward to seeing how these will improve the understanding of a shark's diet and how its digestive system works.

These images and the accompanying assessment appear in the research article "Shark spiral intestines may operate as Tesla valves," published in the Proceedings of the Royal Society B on July 21.

(Photo: Photo by MICHELE SPATARI/AFP via Getty Images)
A black-tip shark is seen swimming during a baited shark dive in Umkomaas near Durban, South Africa, on December 10, 2020. - Aliwal Shoal, a fossilized dune that lies about 4km offshore from the coastal town of Umkomaas, is one of the few places in the world where divers can dive without a cage with Oceanic Blacktip sharks and Tiger Sharks, as the apex predators are attracted by a baited drum filled with sardines.

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Finding Tesla Valves in Shark Intestines

"It's high time that some modern technology was used to look at these really amazing spiral intestines of sharks," says Samantha Leigh, lead author of the study and an assistant professor at California State University Dominguez Hills, 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."

The work involves researchers from the CSU Dominguez Hills, the University of Washington, and the University of California, Irvine. They began with computerized tomography (CT) scanner at the UW's Friday Harbor Laboratories to generate 3D images of shark intestines from preserved specimens stored at the Natural History Museum of Los Angeles. The CT scanner is similar to the one used in hospitals, which takes X-ray images from different angles and combines them with computer processing to create 3D images. The technology allows researchers to examine the internal structure of the shark's digestive system, specifically its intestine, without the need to dissect it.

What they found resembled Tesla valves: which refers to a geometrical design originally intended for check valves, which allow fluids to flow, but in only one direction. They were named after their inventor, Nikola Tesla, who actually called them valvular conduits when he filed them for a patent. Adam Summers, the co-author of the study and a professor at UW Friday Harbor Labs, explains that CT scanning is one of the few ways to understand the structure of shark intestines in 3D. With the complexities of the intestinal structure, having a lot of overlapping layers, doing invasive methods such as dissecting would ruin the structure.

"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," Summers added.

New Insights on How a Shark's Digestive System Works

The spiral structure found in the 3D images is believed to be slow down the movement of food and lead them through the gut, being like Tesla valves aided by gravity and peristalsis or the periodic contraction of their gut muscle.

These discoveries could further understand how sharks eat and digest their food, with sharks known to go for days, even weeks, without food in between huge meals. This suggests that sharks must have the ability to maintain food and nutrition in their systems.