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

Where exactly is the spleen? This internal organ is located in the upper left part of your abdomen (belly). It 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. While it’s not a large organ, it can hold up to three gallons of blood! 

You might not hear as much about the spleen as you do other organs. But it 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 helps maintain your supply of red blood cells. If you have red blood cells that aren’t working properly or are simply too old, it will collect them and get rid of them. As it does so, the spleen recycles the iron from old cells and uses it 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. It also makes chemicals called antibodies that help fight illness.

The spleen is also part of your body’s lymphatic system. This 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 this organ was 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.