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 of time 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 rather remain in the stomach until sufficiently broken down for passing through the valve region, or are regurgitated and spit out. Consequently, shark stomachs often contain items of interest that allow to determine what the animals feed on, as well as non-food items ingested during a feeding frenzy.
Category:Fish anatomy Category:Sharks
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