How well do you know your chicken’s eggs?

Knowing chicken egg anatomy is very useful for more than one reason. In fact, it can tell you a number of things about your hen’s health – for example, whether your hen is stressed or even sick.

So it’s important to know about the different parts so you have a baseline, and if you plan to HATCH eggs, knowing them gets even more important!

This is where chicken egg anatomy comes in the handiest – each part of the egg contributes to whether the embryo will hatch or not.

Anatomy of a chicken egg diagram

Chicken Egg Anatomy Explained

The average Joe knows an egg by the white, the yolk, and the shell. Pretty simple. However, there’s a lot more to those wonderful eggs. Let’s take a look deep inside the egg we know mostly on a surface level.

Air Cell

The air cell is located in the large end of the egg, and it’s what it sounds like – a place where the air is stored.

When you hatch eggs, the air cell and its size become very important. As the egg ages, the air cell becomes larger. This is why older eggs float in water.


When we talk about “egg whites,” we’re referring to the albumen. It contains proteins, niacin, riboflavin, magnesium, potassium, and sodium.

The albumen actually has four layers of thick and thin proteins. It’s truly amazing.

A cloudy albumen means the egg is fresh. As the egg ages, the carbon dioxide escapes, leaving the albumen more transparent than their fresh counterparts.


This is the round white bullseye-looking spot you see in the yolk, and it’s where the embryo begins to develop when the egg is fertilized and under hatching conditions (meaning, the egg is at the right temperature with the proper humidity for hatching.)

Want to know more about how a rooster fertilizes an egg, read this interesting and entertaining article about it.


The bloom of an egg is a natural coating that covers the eggshell and protects the interior of the egg from bacterial invasion. As we all know, bacteria can cause health issues. The bloom also reduces moisture loss from the egg, which is important for the hatching process.  

If you plan to hatch your eggs, you definitely don’t want to wash them, because it will eliminate the bloom.


Pronounced kah-layz-ah, the chalazae are the rope-like strands you see connecting egg whites to the yolk. The more obvious the chalazae are, the fresher the egg.

In nature, it’s an important part of the hatching process because it stabilizes the yolk (which feeds the baby chick embryo as it grows) in the egg.

Shell Membrane, Inner & Outer

The inner and outer membranes provide more protection for the contents of the egg. The air sac is located between these two membranes on the large side of an egg.


The shell protects the albumen and yolk, and eventually the growing embryo. It’s mostly made up of calcium carbonate, which is why feeding your chickens a calcium supplement is so important. The shell is also made up of thousands of tiny pores to allow gas exchange.

Vitelline Membrane

This membrane protects the yolk and keeps it from breaking. It weakens as the egg gets older, which is why yolks of fresh eggs stand up tall, while yolks in older eggs appear flatter.


The egg yolk is a protein, vitamin-rich portion of the egg, and where the embryo begins developing in a fertilized egg. It’s also where 100% of the fat in eggs is contained. Beyond that, it also contains minerals.

In fact, egg yolks contain many essential vitamins such as vitamin D, vitamin A, thiamine, riboflavin, phosphorus, and iron.

Just before chicks are born, they absorb the yolk, which nourishes them for up to 3 days.

Yolk also contains cholesterol and they often get a bad rap for this. But it’s not all bad cholesterol, so keep that in mind.


There you have it! Now you know a lot more detail about the beloved chicken egg. Hopefully, this knowledge will help you beyond watching Jeopardy with your Grandmother. With any luck, it will aid you in hatching more successfully at the very least.

Curious about egg abnormalities like wrinkled shells, rubber eggs, and lash eggs? Read this article on abnormal eggs.


Maat van Uitert is a backyard chicken and sustainable living expert. She is also the author of Chickens: Naturally Raising A Sustainable Flock, which was a best seller in it’s Amazon category.  Maat has been featured on NBC, CBS, AOL Finance, Community Chickens, the Huffington Post, Chickens magazine, Backyard Poultry, and Countryside Magazine. She lives on her farm in Southeast Missouri with her husband, two children, and about a million chickens and ducks. You can follow Maat on Facebook here and Instagram here.

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One Comment

  1. This was very informative and educational! I think I have had at least one of each of the ten eggs described at one time or another from my chickens and was scratching my head with the “what the?” kind of confusion. You certainly answered a lot of questions for me. I will definitely take pictures of my next strange egg and send it to you.
    Thank you so much for all your great information it has helped me become a much better chicken owner!

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