Allantois | |
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Details | |
Pronunciation | /əˈlæntɔɪs/, /əˈlæntoʊɪs/ |
Days | 16 |
Identifiers | |
Latin | allantois |
MeSH | D000482 |
TE | E6.0.1.2.0.0.2 |
Anatomical terminology |
The allantois (/əˈlæntoʊɪs/ a-LAN-toe-iss;[1] pl.: allantoides or allantoises) is one the extraembryonic membranes arising from the yolk sac. It is a hollow sac-like structure filled with clear fluid that forms part of the developing conceptus in an amniote that helps the embryo exchange gases and handle liquid waste. The other extraembryonoic membranes are the yolk sac, the amnion, and the chorion. In mammals these membranes are known as fetal membranes.
The allantois, along with the amnion, chorion, and yolk sac (other extraembryonic membranes), identify humans and other mammals, birds, and reptiles as amniotes. These extraembryonic membranes that form the embryo have aided amniotes in the transition from aquatic to terrestrial environments.[2] Fish and amphibians are anamniotes, lacking the allantois.