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Spiral valve

This article is about the intestinal structure. For other uses, see Spiral valve (disambiguation).
The spiral valve of a nurse shark (Ginglymostoma cirratum).

A spiral valve or scroll valve is the corkscrew-shaped lower portion of the intestine of some sharks, Acipenseriformes (sturgeon and paddlefish), rays, skates, bichirs, Lepisosteiformes (gars), and lungfishes.[1] A modification of the ileum, the spiral valve is internally twisted or coiled to increase the surface area of the intestine which increases nutrient absorption.[2]

Description

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The intestines of a shark are much shorter than those of mammals. Sharks have compensated for this problem by having a spiral valve, or a scroll valve, inside the intestine to increase the absorbent surface of the intestine. By keeping digestible material in the ileum for an extended period maximum nutrient absorption is ensured. For this reason, many sharks and related fish feed very infrequently. The food passes into the comparatively short colon of the shark almost fully digested, and then out the cloaca and vent.

A consequence of the spiral valve constricting the lumen of the ileum is that sharks cannot pass large hard objects (such as bones) through their lower intestine. Such objects instead remain in the stomach until sufficiently broken down for passing through the valve region, or are regurgitated. Consequently, shark stomachs often contain items of interest that enable one to determine what the animals feed on, as well as non-food items ingested during a feeding frenzy.

Sharks also possess a rectal gland that removes excess salt.

Applications

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The spiral valve has been analogized to a Tesla valve.[3] Researchers in biomimetics have used a design inspired by the spiral valve to create a soft pipe with no moving parts, in which fluid flows is more likely to flow one way than the other. The softness is necessary, as there is a mathematical theorem stating that in a completely a undeformable pipe, fluid is equally likely to flow forwards or backwards.[4][5]

See also

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References

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  1. ^ Olsson, Catharina (2024). "Gut anatomy". Encyclopedia of Fish Physiology. pp. 339–347. doi:10.1016/B978-0-323-90801-6.00106-3. ISBN 978-0-323-99761-4.
  2. ^ Reece, Jane B. (2011). Campbell Biology. Benjamin Cummings / Pearson. p. 752. ISBN 978-0-321-55823-7.
  3. ^ Leigh, Samantha C.; Summers, Adam P.; Hoffmann, Sarah L.; German, Donovan P. (2021-07-28). "Shark spiral intestines may operate as Tesla valves". Proceedings. Biological Sciences. 288 (1955): 20211359. doi:10.1098/rspb.2021.1359. ISSN 1471-2954. PMC 8292776. PMID 34284626.
  4. ^ Levin, Ido; Sadaba, Naroa; Nelson, Alshakim; Keller, Sarah L. (October 2024). "Asymmetric fluid flow in helical pipes inspired by shark intestines". Proceedings of the National Academy of Sciences. 121 (40): e2406481121. doi:10.1073/pnas.2406481121. PMC 11459177. PMID 39316056.
  5. ^ Ouellette, Jennifer (2024-09-26). "These 3D-printed pipes inspired by shark intestines outperform Tesla valves". Ars Technica. Retrieved 2025-08-06.
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