The Human Digestive System

by Karthik Gurumurthy

When you bite down on a sandwich, your teeth break it into smaller pieces that are easy to swallow. at the same time, a liquid , called saliva (spit), rushes into your mouth. Saliva contains chemicals called enzymes that mix with the food and start to digest it.

Your swallowed food travels down your esophagus, a tube that leads to your stomach. The esophagus is surrounded by muscles that move like a wave to push the food towards stomach. Because of this muscle movement, called peristalsis, you could eat food even if you were upside down and it would still get to your stomach.

Food spends a few hours in the stomach, where it is churned up with more enzymes and acidic “gastric juices.” Eventually, it all becomes a thick soup of partially digested food and chemicals, called chyme. The chyme enters the small intestine, a narrow, winding tube, where it encounters yet more digestive chemicals made by two organs, the liver and pancreas. The chemical finish digesting the last bits of food.

Any remaining material-indigestible food, excess nutrients, and water-is passed into the large intestine, a wide, muscular tube. Water is absorbed from the large intestine, and the rest is stored as solid waste until it can leave the body.

Nutrients are small enough to pass through the walls of the digestive organs and into capillaries, where blood transports them to cells. Extra nutrients are stored in the liver. Some food is easily digested and passes into the blood from  the mouth and stomach. Most food takes longer to digest, and therefore, most nutrients are absorbed into the blood through the walls of the small intestine.