Download Avian Extra-embryonic membranes

Avian Extra-embryonic membranes
Because the avian embryo has no anatomical connection to the hen, all of its
nutritive requirements except oxygen must be contained in the egg. The
embryo very early in its development develops special membranes external
to its body to access the nutrients in the egg and to carry out essential body
functions.
There are four of these special membranes and their names and functions are
as follows:
Yolk sac: This sac envelops the yolk and produces an enzyme that changes
the yolk material to a form that can be used as a food source by the
developing embryo. Any remaining, unused yolk material in the yolk sac
when the chicken hatches from the egg is drawn into the abdomen for use by
the chicken for the first two to three days after hatching while the chicken
learns what to eat/drink and where to find it.
Amnion: The amnion forms a sac that is filled with fluid in which the
embryo floats. In this way it provides a shock-absorbing environment in
which the fragile embryo can develop without harm from normal day to day
knocks.
Allantois: The allantois develops an extensive circulatory system connected
to that of the embryo and driven by the new embryonic heart. When the
allantois is fully developed it completely surrounds the embryo. This
membrane has a number of functions:
Respiratory - the developing embryo uses oxygen and produces carbon
dioxide i.e. it has respiration. It is unable to carry out this function itself and
hence the allantois oxygenates the blood and eliminates the carbon dioxide.
Excretory - it removes the wastes that result from the embryo’s metabolism
and deposits it in the allantoic cavity.
Digestive - it provides the means for the embryo to access the albumen and
the calcium of the shell.
Chorion: The Chorion fuses the inner shell membrane to the allantois and
helps that membrane to carry out its functions.