Digestive System

The digestive system is the group of body parts that breaks food down into tiny pieces the body can use. It turns a sandwich into fuel for your muscles, building blocks for your bones, and energy for your brain. The system runs from your mouth all the way to the other end of your body. Food takes about one to three days to make the full trip.

Digestion starts in your mouth. Your teeth grind food into smaller chunks. Your tongue mixes it with spit, also called saliva. Saliva is not just water. It contains chemicals called enzymes that begin to break down starches in food like bread and crackers. Once the food is mashed and wet, you swallow.

The food then slides down a tube called the esophagus. Muscles in the walls of the esophagus squeeze in waves to push the food along. These muscles are so strong that you could swallow while standing on your head, and the food would still reach your stomach.

Your stomach is a stretchy bag about the size of your fist when empty. It can stretch to hold about a quart of food, roughly the size of a large soda bottle. The stomach mixes food with strong acid and more enzymes. The acid is strong enough to dissolve metal, but a thick layer of mucus protects the stomach wall from being eaten away. After a few hours, the food becomes a thick soup called chyme.

Next, the chyme moves into the small intestine. Despite its name, the small intestine is the longest part of the system. It is about 22 feet long, coiled up inside your belly. The liver and pancreas pour in special juices that finish breaking the food down. Tiny finger-like bumps on the inside walls, called villi, soak up the nutrients. Those nutrients enter your blood and travel to every cell in your body.

Whatever your body cannot use moves into the large intestine. This part is shorter, about five feet long, but wider. It pulls water back out of the leftovers so you do not get dehydrated. Friendly bacteria living there help break down what is left and even make some vitamins for you. There are trillions of these bacteria. They outnumber the cells of your own body.

The leftover waste, now solid, leaves the body through the rectum and anus as poop. The whole journey, from the first bite to the final exit, takes one to three days. While you sleep, eat, play, and learn, your digestive system is quietly working the entire time.