Allantois

Allantois (Greek ho Allas, allántos " sausage -shaped " ) is called the embryonic urinary bladder in reptiles, birds and mammals. It is a protrusion of the embryonic rectum and uses include the storage of oxidizing water and other metabolic end products. The allantois is often streaked with blood vessels.

Humans and other mammals

The allantois arises when people on the 16th day after conception from the hypoblast and is usually only temporary -existent. It covers first as Allantoic diverticulum in the extraembryonic mesoderm of the body stalk ( engl. body stalk ) - the later umbilical cord of the embryo - into it. The Allantoic diverticulum enlarges hardly in the human embryo and closes the urachus. Forms in humans, the allantois is not fully reversible, then a urachal fistula remain which establishes a full connection between the bladder and umbilicus.

In most other mammals, the Allantoic diverticulum is surrounded by a large bag of mesodermal origin, the allantois, which lies in the chorionic cavity and the entire amniotic cavity (eg predators, horses) or only a portion (eg, Artiodactyla ) surrounds them. The allantois forms by their connection to the chorion ( Allantochorion ) with the placenta.

In the domestic fowl the allantois after five days incubation period is already about as big as the embryo and has already penetrated the amnion. It then grows in the egg toward the air chamber and enters into contact with it. Thereafter, the gas exchange between the embryo and the surroundings of the ice to a large extent on the allantois is running. The growth continues and the allantois touched shortly before hatching of the chick inside almost the entire egg surface. At this stage the allantois also contributes to reduce the necessary calcium for bone formation of the shell. This process is mediated by the exhaled carbon dioxide and moisture in the pan. When you slip the allantois is destroyed and the one remaining content wetted the chick with the remaining liquid from the amnion ( amniotic fluid ).

Reptiles

The ratios in reptiles are similar to those of birds. In some species, such as the viviparous sea snakes of the genus Enhydrina, the allantois functions as a placenta ( allantoic placenta).

Swell

  • P. Fioroni: General and Comparative embryology of animals. Springer Berlin 1992.
  • T. Schiebler et al. ( Ed. ): anatomy. Springer Berlin, 6th Edition 1995.
  • Detlev Drenckhahn (ed.): Benninghoff, anatomy. 17th edition 2008 Urban & Fischer Verlag, ISBN 9783437423420, volume 1, page 228
  • Monika Kressin, Bertram Schnorr: Embryology of Domestic Animals. Enke Verlag, Stuttgart, 5th edition, 2006. ISBN 3-8304-1061-1
  • Amniotic sac
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