Paper, Shark spiral intestines may operate as Tesla valves

Abstract: Looking to nature for inspiration has led to many diverse technological
advances. The spiral valve intestine of sharks has provided the opportunity
to observe the efficiency of different valve systems. It is supposed that the
spiral intestine present in sharks, skates and rays slows the transit rate of
digesta through the gut and provides increased surface area for the absorption of nutrients. In this investigation, we use a novel technique—creating
three-dimensional reconstructions from CT scans of spiral intestines—to
describe the morphology of the spiral intestine of at least one species from
22 different shark families. We discuss the morphological data in an
evolutionary, dietary and functional context. The evolutionary analyses
suggest that the columnar morphology is the ancestral form of the spiral
intestine. Dietary analyses reveal no correlation between diet type and
spiral intestine morphology. Flow rate was slowed significantly more when
the two funnel-shaped spiral intestines were subjected to flow in the posterior
to anterior direction, indicating their success at producing unidirectional flow,
similar to a Tesla valve. These data are available to generate additional threedimensional morphometrics, create computational models of the intestine, as
well as to further explore the function of the gastrointestinal tract of sharks in
structural and physiological contexts.

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