The inside of a shark is full of curiosities, starting with rows of hardworking teeth that can be replaced with new ones for a lifetime. But far below the digestive tract—in fact, just before the shark is finished—is another strange structure: the spiral gut, an intricate ladder made of shark meat.
Scientists have speculated that sharks have intestines so intricately shaped to slow digestion, extracting every last calorie from their prey. This may also be one reason why sharks can spend a long time between meals.
but at In Proceedings of the Royal Society B on WednesdayIn this study, researchers published the most detailed look ever at those spiral intestines by turning a CT scanner on them, revealing the complex internal geography of more than 20 species of sharks. After filling the intestines with fluid, he also made a discovery: some of them act like natural versions of a valve that Nikola Tesla 1920. patented in, pulling the fluid forward in one direction without moving the parts.
Samantha Leigh, an assistant professor at California State University in Dominguez Hills, who led the new study, said researchers studying the shark’s spiral intestines often refer to a set of 1885 anatomical drawings. Or they may dissect the intestines themselves, affecting the structural integrity of the organ in service of a closer look. To fully visualize the structures, she and her colleagues carefully removed the intestines of several shark species and imaged them in a CT scanner.
Sharks’ spiral intestines come in four flavors—a basic spiral, a nested series of funnels pointing to one side, a nested series of funnels pointing to the other, and what’s called a scroll gut, where the layered sheaths overlap each other roam inside. In CT scans, the vortices and folds of the structures are clearly visible.
It didn’t matter what the shark ate in the shape of its intestine—bonnethead sharks, which eat both plants and other animals, had a scroll gut, as did carnivorous hammerheads.
Then the researchers attached some spiral intestines to the tubes and watched a mixture of water and glycerol flow through them. They found that fluid, in fact, moves more slowly through the spiral than through the straight part of the shark’s intestine, supporting the idea that the spiral gut helps the shark prolong its digestion time.
However, they also found that the funnel was a preferred direction for flow in the intestines. Fluid entering one end flows much more slowly than fluid entering the other, meaning that the gut within the animal acts like a one-way street. In mammals, muscle contractions produce this effect. But in sharks, the structure of the gut itself can help.
In fact, the shape of the funnel gut recalls the loops of a Tesla valve, a type of pipe that was patented by a Serbian-American inventor.
“The purpose of the valve was to produce flow in one direction without the use of additional mechanical parts or additional additional energy,” Dr. Leigh said. “It seems that these sharks are very similar in size to the intestines.”
Structures honed by ages of development could provide inspiration to engineers – manta ray’s spectacular uncloggable filters, for example, could provide a way to flush out plastic pollution before it reaches waterways. In the case of shark intestines, Dr. According to Leigh, who also studies the effects of microplastic pollution on fish, it could be that more information about how the intestines work could inform the filters as well.
“My hope is to find out what these particular morphologies are good at moving forward, what they are good at filtering out,” said Dr. Leigh. Perhaps somewhere along the line, shark intestines may inspire devices to help passively remove plastic from water, simply because of the way they are made.