The inside of a shark is full of curiosities, starting with rows of hardworking teeth that can be replaced by fresh ones throughout its life. But quite a bit farther down the digestive tract — in fact, right before the shark ends — lies another odd structure: the spiral intestine, an intricate staircase made of shark flesh.
Scientists have speculated that sharks have such intricately shaped intestines to slow down digestion, eking every last calorie out of their prey. It may even be one reason sharks can go a long time between meals.
But on Wednesday in the Proceedings of the Royal Society B, researchers published one of the most detailed looks at those spiral intestines so far by turning a CT scanner on them, revealing the complex inner geographies of more than 20 species of sharks. After filling the intestines with fluid, they also made a discovery: Some of them function like natural versions of a valve that Nikola Tesla patented in 1920, drawing fluid ever onward in one direction without moving parts.
Samantha Leigh, an assistant professor at California State University, Dominguez Hills who led the new study, said that researchers who study sharks’ spiral intestines often refer to a set of 1885 anatomical drawings. Or they may dissect the intestines themselves, marring the organ’s structural integrity in the service of getting a closer look. To see the structures whole, she and her colleagues carefully removed the intestines of numerous shark species and imaged them in a CT scanner.