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((Short description|Part of a shark intestine))
((about|the intestinal structure||))
((Refimprove|date=August 2018))
[[File:Spiraldarm des Karibikammenhai (Ginglymostoma cirratum).jpg|thumb|The spiral valve of a [[nurse shark]] (''Ginglymostoma cirratum'').]]

A '''spiral valve''' or '''scroll valve''' is the corkscrew-shaped lower portion of the [[gastrointestinal tract|intestine]] of some [[shark]]s, [[Acipenseriformes]] ([[sturgeon]] and [[paddlefish]]), [[batoidea|ray]]s, [[Skate (fish)|skate]]s, [[bichir]]s, [[Lepisosteiformes]] (gars), and [[lungfish]]es. 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.<ref>Campbell Reece, ''Biology'', 9th edition, p. 752</ref>

== Description ==
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 [[digestion|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 (anatomy)|colon]] of the shark almost fully digested, and then out the [[cloaca]] and vent.

A consequence of the spiral valve constricting the [[Lumen (anatomy)|lumen]] of the ileum is that sharks cannot pass large hard objects (such as [[bone]]s) through their lower intestine. Such objects instead remain in the [[stomach]] until sufficiently broken down for passing through the valve region, or are [[Regurgitation (digestion)|regurgitate]]d. 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.

==See also==
((Portal|Sharks))
* [[Small intestine]]
* [[Physical characteristics of sharks]]

==References==
((reflist))

((diversity of fish))

[[Category:Fish anatomy]]
[[Category:Sharks]]

((Shark-stub))

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