The small intestine is a long, coiled tube in your digestive system where most of the nutrients from your food get absorbed into your bloodstream. Despite its name, the small intestine is actually the longest part of your digestive tract, stretching about 20 feet if you could uncoil it completely. It's called “small” because it's narrower than the large intestine, not because it's short.

After your stomach breaks down food into a soupy mixture, that mixture moves into your small intestine. The inner walls are covered with millions of tiny, finger-like projections called villi that work like miniature sponges, pulling nutrients out of the digested food and passing them into your blood. These nutrients, like proteins, vitamins, and minerals from your lunch, then travel through your bloodstream to every cell in your body, giving you energy to run, think, and grow.

The small intestine has three sections: the duodenum (where most chemical digestion happens), the jejunum, and the ileum. By the time food finishes its journey through the small intestine, your body has extracted almost everything useful from it. The leftover material then moves into the large intestine.