We're diving deep inside the body today to take a closer look at an important organ. Is it the pancreas? The liver? Nope! Today's Wonder of the Day is all about the spleen!

Why the spleen? Here at Wonderopolis, we say, “Why not?" Some Wonder Friends were WONDERing about the spleen and that made us WONDER, too. So now we can all WONDER about the spleen together!

The spleen is an internal body organ located in the upper left part of your abdomen (belly). The spleen sits behind and is protected by your ribs.

If you could see your spleen, it would be about the same size and shape as your fist. It's soft and dark purple/red. Although it's not a large organ, it can hold up to three gallons of blood! We urge you to keep your spleen right where it is, though, and simply look at pictures of spleens if you want to see what they look like.

Although you don't hear as much about the spleen as you do other organs, such as the heart, the spleen does several important things for your body. Before you were born, your mother's spleen worked hard to make all of your red blood cells.

Today, your spleen still works hard to maintain your supply of red blood cells. If you have red blood cells that aren't working properly or are simply too old, your spleen will collect them and get rid of them. As it does so, it recycles the iron in the red blood cells that it gets rid of and uses them to help make new, healthy red blood cells.

The spleen is also an important part of your body's immune system. It makes special white blood cells — called macrophages and lymphocytes — that help protect your body from infections. Your spleen also makes chemicals called antibodies that help fight infections.

The spleen is also part of your body's lymphatic system. The lymphatic system helps keep your body's fluid levels in balance. The spleen helps to remove excess lymph — a clear fluid that carries proteins and other important substances around the body — and returns it to the blood.

Sometimes people develop problems with their spleens. When this happens, a doctor may have to remove it during a surgery called a splenectomy. You can live without your spleen, but you may be more likely to get certain infections in the future.

In the past, many people held some weird beliefs about their spleens. Before modern medicine, many people believed their spleens were responsible for making them angry or sad. If you were in a bad mood, some people might have accused you of suffering from “vapors" caused by your spleen! Of course, we now know better thanks to science.

Wonder What's Next?

Tomorrow’s Wonder of the Day might have you singing, “Let it rain!”