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The interior of a shark is full of curiosities, starting with rows of laborious teeth that can be replaced with new ones throughout its life. But a little further up the digestive tract – in fact, just before the shark’s end – is another strange structure: the spiral gut, an intricate staircase made of shark flesh.
Scientists have speculated that sharks have intestines so complex that they slow down digestion, removing even the last calorie from their prey. This may even be one of the reasons sharks can stay between meals for a long time.
But on Wednesday in the Proceedings of the Royal Society B, researchers published one of the most detailed looks at these spiral intestines so far by rotating a scanner over them, revealing the complex internal geographies of more than 20 species of sharks. After filling the intestines with fluid, they also made a discovery: some of them function as natural versions of a valve patented by Nikola Tesla in 1920, sucking fluid always in a direction with no moving parts.
Samantha Leigh, assistant professor at California State University, Dominguez Hills, who led the new study, said researchers studying shark spiral intestines often refer to a set of 1,885 anatomical drawings. Or they can dissect the intestines themselves, marring the structural integrity of the organ in the service of further examination. To see the entire structures, she and her colleagues carefully removed the intestines of many species of sharks and imaged them in a CT scanner.
Shark spiral intestines come in four flavors: a basic spiral, a series of interlocking funnels pointing one way, a series of interlocking funnels pointing the other way, and what is known as a spiral gut. , where the layered sheaths nestle within each other. In CT scans, the whorls and folds of the structures stand out clearly.
It doesn’t matter what a shark ate in terms of the shape of its gut – flathead sharks, which eat both plants and other animals, had scrolled gut, just like carnivorous hammerhead sharks. .
Next, the researchers plugged spiral intestines into tubes and observed a mixture of water and glycerol pass through them. They found that indeed, the fluid moved more slowly in the spiral than in a straight section of the shark’s intestine, supporting the idea that the spiral intestines help sharks extend their digestion time.
However, they also found that the intestines of the funnel had a preferred direction for the flow. Fluid entering one end flowed much more slowly than fluid entering the other, implying that inside the animal, the intestine functions as 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-shaped intestine is reminiscent of the loops of the Tesla valve, a kind of hose patented by the Serbian-American inventor.
“The purpose of the valve was to produce flow in one direction without the use of additional mechanical parts or additional energy,” Dr. Leigh said. “It looks very similar to the way these shark intestines are shaped.”
The structures perfected by eons of evolution can be a source of inspiration for engineers – the spectacularly non-clogging filters of the manta ray, for example, can provide a means of filtering plastic pollution before it reaches the clouds. streams. In the case of shark intestines, said Dr Leigh, who also studies the effects of microplastic pollution on fish, it may be that additional information about how the intestines work may also inform the filters.
“My hope is to understand what these particular body types are good for moving around, what they’re good for filtering,” said Dr Leigh. Perhaps somewhere along the line, shark intestines could inspire tools to help passively remove plastics from water, simply because of the way they’re constructed.
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