Dear Dr. Universe: How does digestion work? –Abi, 12, U.S.; Megha R., 11, Dubai

Dear Abi and Megha,

All around the world, animals are eating all kinds of different foods. Our foods might be different, but one thing is true for all of us: We have to digest.

I decided to visit my friend Bob Ritter to find out how this works. He’s a researcher here at Washington State University who is really curious about the connections between our brain and stomach.

“What we eat at lunch is almost completely digested by the time we are ready to eat dinner,” he said. “It is digested, absorbed, and the food has totally changed.”

The molecules that make up a piece of meat or a vegetable on your plate are too big for your body to use, at least at first. The body breaks down the food using a nearly 30-foot-long digestive tract that runs from your head to your rear end.

And while we may all digest, different animals have different kinds of tracts. Ritter explained that a python could go for about six months without food. When it comes time to eat a meal, usually in a single gulp, the python’s digestive system will suddenly grow bigger.

Unlike pythons, humans need to eat much more often. The human digestive system can help you digest a meal in just a few hours or less.

Muscles in your stomach squeeze and occasionally grumble to tell your brain that you’re hungry. When you smell or even see food, your mouth starts to water. Even the sound of food going into my bowl makes my mouth water. This saliva helps us soften and break down food so we can swallow it.

The muscles in the esophagus, a long tube in your throat, help push food down into your stomach. There, your stomach acids and enzymes help you break down the food. Most of the food is now about the size of a grain of salt.

These little pieces move onto the small intestine, which is pretty big, despite it’s name. It’s here where the big chemicals in food are broken down to small ones that the body can absorb into your blood, like sugars, amino acids, and fatty acids.

There is a lot of surface area that makes it possible for your body to absorb these helpful nutrients, too. If you unfolded your small intestine on a flat surface, it would likely cover a tennis court, Ritter said.

Once the nutrients are absorbed, the large intestine absorbs water from the digested mix and helps give it back to your body. Some harder parts are left behind and get ready to leave the body. Pretty soon, nature calls.

Whether you are a cat, a python, or a human, the digestive system not only fuels your body, but also protects it. Humans even have a special lining in their stomach that gets replaced every few days to protect them from invaders like toxins or bacteria. It’s something to chew on the next time you sit down for dinner.

Sincerely,
Dr. Universe

Ask Dr. Universe is a science-education project from Washington State University. Send your own question to Dr. Universe at AskDrUniverse.wsu.edu.