What is an egg? – An information nest


Do you really know what an egg is made of? Here is a diagram to see more clearly!

An egg is made up of several elements:

First of all we have the shell. The latter has a protective role, in particular against pathogens (in particular salmonella, etc.). The shell takes shape in the oviduct by deposit of calcium carbonate and its color differs according to the species. We also find two membranes which are like a second protection against potential intruders. One is glued to the shell while the other to the albumen (which corresponds to the white of the egg).

Inside the egg, we find albumen which is a translucent liquid, composed of almost 90% water as well as proteins including albumin, mineral salts and maternal antibodies.

We then distinguish, of course, the yellow, rigorously called vitellus. It is a real source of vitamins, minerals and lipoproteins. The yolk will be the main, if not the only, energy reserve necessary for embryonic growth. It is surrounded by the vitelline membrane which helps maintain the integrity of the yolk. The latter also acts as a barrier to possible pathogens.

On the yolk, we observe the germinal disc which constitutes the entry point of the spermatozoa. This is where the potential fertilization takes place.

Finally, we have the chalazes which are white filaments wound in a spiral allowing the maintenance of the yolk in the center of the egg. They act like springs.

And finally, at the end of the egg, we have the inner tube. This takes more and more volume over time (this is also why an old egg floats when you put it in water). This chamber is essential since it is inside it that the embryo will take its first breath at the time of hatching …

There you go, I hope I taught you something today!


Gaëlle Dobignard, May 2018, Eggs Anatomy, Available online: https://oeuf-poule-poussin.com/eggs-anatomy/, consulted 03/07/21

© Morgane Virapin – March 2021


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