Spiral valve
Encyclopedia
A spiral valve is the lower portion of the intestine
of some shark
s, ray
s, skate
s and bichir
s. 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.
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 digest
ible 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 bone
s) through their lower intestine. Such objects rather remain in the stomach
until sufficiently broken down for passing through the valve region, or are regurgitate
d 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
.
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
of some shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s, ray
Batoidea
Batoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...
s, skate
Skate
Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. There are more than 200 described species in 27 genera. There are two subfamilies, Rajinae and Arhynchobatinae ....
s and bichir
Bichir
The bichirs are a family, Polypteridae, of archaic-looking ray-finned fishes, the sole family in the order Polypteriformes.All species occur in freshwater habitats in tropical Africa and the Nile River system, mainly swampy, shallow floodplains and estuaries.-Anatomy and appearance:Bichirs are...
s. A modification of the ileum
Ileum
The ileum is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum.The ileum follows the duodenum...
, the spiral valve is internally twisted or coiled to increase the surface area of the intestine, to increase nutrient absorption.
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 digest
Digest
Digest can refer to any of the following:*A condensed collection or compendium of writings:**Pandects, or "The Digest", a digest of Roman law**A tax digest...
ible material in the ileum for an extended period of time maximum nutrient absorption is ensured. For this reason, many sharks and related fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
feed very infrequently. The food passes into the comparatively short colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
of the shark almost fully digested, and then out the cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...
and vent.
A consequence of the spiral valve constricting the lumen
Lumen (anatomy)
A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...
of the ileum is that sharks cannot pass large hard objects (such as bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s) through their lower intestine. Such objects rather remain in the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
until sufficiently broken down for passing through the valve region, or are regurgitate
Regurgitation (digestion)
Regurgitation is the expulsion of material from the mouth, pharynx, or esophagus, usually characterized by the presence of undigested food or blood.Regurgitation is used by a number of species to feed their young...
d 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
Feeding frenzy
In ecology, a feeding frenzy is a situation where oversaturation of a supply of food leads to rapid feeding by predatory animals. For example, a large school of fish can cause nearby sharks to enter a feeding frenzy. This can cause the sharks to go wild, biting anything that moves, including each...
.