What is an Allantois?

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  • Written By: Amy Hunter
  • Edited By: Bronwyn Harris
  • Last Modified Date: 06 November 2019
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The allantois is a membrane that is present in the embryonic stage of mammals, reptiles and birds. The allantoic membrane is designed to help the fetus survive, removing waste from the animal. Both liquid waste and gases that the embryo have used are exchanged through this membrane. The allantois contains a network of blood vessels that the animal uses to remove waste products from the body.

Although many different animals have an allantoic membrane, they are not exactly the same. In birds and reptiles, the allantoic membrane not only removes waste from the embryo, but also helps to provide oxygen. Despite the appearance that the shell of an egg is solid, it can be permeated by oxygen. The allantois absorbs the oxygen that enters the egg and transmits it to the embryo.

The majority of mammals deliver live young. In these animals the allantois is an early part of the umbilical cord. In many mammals, the allantois eventually develops into the umbilical cord. In human embryos, the allantois develops as part of the digestive system early in conception. It matures into the umbilical cord, which is responsible for providing nutrients and removing waste.


Animals that have an allantoic membrane are called amniotes. In addition to the allantois, they also have an amnion and a chorion, which are both embryonic membranes. The amnion is a membrane that protects the embryo from damage during the gestation period. The other membrane that amniotes have in common is the chorion. The chorion is responsible for transferring nutrients between the mother and embryo. This transfer is made through the circulatory system.

In addition to the reptiles, mammals and birds that make up the group known as amniotes, there was previously a larger group of animals that belonged to this group as well. Dinosaur embryos contained allantoic membranes, making them amniotes as well. The allantois, chorion and amnion are formed during the earliest period of the gestation period. These membranes are a vital part of the development of the embryo. Problems with any of these membranes can lead to a loss of viability of the embryo.


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