Spiral casing

from Wikipedia, the free encyclopedia
Spiral intestine of the Caribbean nurse shark ( Ginglymostoma cirratum ), partially cut open. Access from the stomach on the right, exit to the rectum on the left.

The spiral intestine , also intestinum spirale , is an organ of lower fish and occurs in sharks , rays , short-nosed chimera and some original bony fish (non- teleostei ). In these vertebrates, the enlargement of the inner surface of the intestine necessary for digestion is not achieved by lengthening the intestine and forming loops, as in real bony fish and terrestrial vertebrates , but by a fold in the short, cigar-shaped and straight intestine that is wound like a narrow spiral staircase. There can be a maximum of almost 60 whorls. But there are also spindle-less and roulade-like rolled spiral folds.

The name has been naturalized (since Rathke 1824) - but it is imprecise, a real (double) intestinal spiral like that of tadpoles is rare, e.g. B. with bitterling . In Campostoma anomalum ( Cyprinidae ) the midgut is "wrapped" around the swim bladder approx. Eight times (screwed). However, these cases have nothing to do with the “real” spiral casing.

In terms of evolutionary history, the spiral bowel is the result of an enlargement of the digestive and resorbing surface of the mucous membrane , and thanks to its high internal stability (in the sense of Wolfgang Friedrich Gutmann ) it also provides mechanical support for the chorda dorsalis . This function could be omitted again in more highly developed taxa, since the spine took over it more and more.

The spiral bowel is undoubtedly an ancient ( plesiomorphic ) feature of the jaw mouths , perhaps even of the vertebrates . Spiral coprolites are already known from Arthrodira ; Lampreys have at least one "spiral" (screw) fold, which perhaps represents a regression from a spiral intestine. (Only the hagfish have nothing of the kind (primarily?), Just irregular, coarse folds of the mucous membrane.) In sharks , the spiral bowel begins right behind the stomach and makes up the entire midgut . In the case of sturgeon , on the other hand, we already find a midgut loop, the "intermediate intestine"; the spiral bowel is restricted to its descending branch. Amia has four entrances left, Lepisosteus practically none; s. also Chirocentrus .

swell

  • Spiral casing. In: Lexicon of Biology. Volume 8, Herder, Freiburg im Breisgau 1987, ISBN 3-451-19648-4 .
  • Kurt Fiedler: Textbook of Special Zoology. Volume II, Part 2: Fish . Gustav Fischer Verlag, Jena 1991, ISBN 3-334-00339-6 .