Generic selectors
Exact matches only
Search in title
Search in content
Search in posts
Search in pages
Filter by Categories
Announcement
Basketball
Boston Marathon
Boys and Girls Champs
Caribbean
Caribbean Premier League
Celebrity
Comedy
Cricket
Earthquake Haiti
Elections
Games
Gibson-McCook Relays
Gold Cup
Investment
Jamaica
Manning Cup
Marketplace
News
Olympics
Prayer
Reggae Music
Religion/Faith
Soccer
Sports
Tennis
Track and Field
Trinidad & Tobago
Uncategorized
United States
World
World Championships
World Cup
Yowlink

Spiral valve

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. A modification of the ileum, the spiral valve is internally twisted or coiled to increase the surface area of the intestine, to increase nutrient absorption.[1]

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 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 rather 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.

See also

References

  1. ^ Campbell Reece Biology, 9th edition, page 752