chicken placenta?

Question

I know what the placenta for a human baby is...but what serves as the placenta for a chicken egg? Is it the chorion? I know it's not the shell, because the shell doesn't provide any oxygen and nutrients - it only protects the embryo.

Answer 1

Hm. Let's look at it this way. A placenta normally allows access to nutrients and waste disposal, but also filters that access in a way most beneficial to the fetus.

In a chicken, you'll end up with different things depending on which aspects you're focusing on. The allantois collects waste from an embryo, and in non-placental animals like chickens it also serves to distribute oxygen. In placental animals, the allantois becomes the umbilical cord... so arguably it's more analogous to that than the placenta itself.

Of course, the most obvious interface with the egg and the external environment, like the placenta, IS the shell. And the shell DOES do some of the functions of the placenta, such as allowing good things to pass (oxygen) while keeping bad things out (arguably, it's even MORE protective than a human placenta).

It's not really a living tissue, like the placenta, though... the nearest thing you'll get to the outside that's alive is the chorion. In placental animals, part of the chorian does develop into part of the placenta (along with some of the allantois)... but most of it does not. The chorion engages in some of the exchange on the outside that assists the allantois. It's not a great match, but maybe it's as close as you're going to get.

Answer 2

The egg contains all the nutrients the chick needs until it hatches. Oxygen can pass from the air through the eggshell.

Answer 3

I think it's all in the embryo dude!