Allantois (plural allantoides or allantoises)
is a part of a developing animal
conceptus (which consists of all
embryonic and extra-embryonic tissues). It helps the embryo
exchange gases and handle liquid waste.
The allontois, along with the
chorion (other embryonic membranes), identify humans as
amniotes, along with
This sac-like structure is primarily involved in
excretion, and is webbed with
The function of the allantois is to collect liquid waste from
the embryo, as well as to exchange gases used by the embryo.
In reptiles, birds, and monotremes
The structure first evolved in
as a reservoir for nitrogenous waste, but also as a means for
oxygenation of the embryo.
Oxygen is absorbed by the allantois through the
egg shell. The allantois functions similarly in
monotremes, which are egg-laying
In most marsupials
marsupials, the allantois is avascular, having no blood
vessels, but still serves the purpose of storing nitrogenous
Also, most marsupial allantoises do not fuse with the
chorion. An exception is the allantois of the
bandicoot, which has a vasculature, and fuses with the
In placental mammals
placental mammals, the allantois is part of and forms an
axis for the development of the
mouse allantois consists of
mesodermal tissue, which undergoes vasculogenesis to
form the mature umbilical artery and vein.
human allantois is an
endodermal evagination of the developing
hindgut which becomes surrounded by the
mesodermal connecting stalk. The connecting stalk forms
the umbilical vasculature. These endodermal and mesodermal
tissues together form the human umbilical cord. The
allantois later becomes the
urachus, a vestigial structure with an unknown function.
A patent allantois can result in
The word comes from the Greek word for
which the allantois resembles.
Downs, K.M. 1998. "The Murine Allantois". Current Topics
in Developmental Biology vol. 39, pp 1-33.
Dorland's Medical Dictionary