A villus (plural: villi) is a tiny, finger-like projection that lines the inside of your small intestine. Imagine millions of microscopic fingers reaching into the space where your digested food passes through. These villi create an enormous surface area, like turning a smooth tube into something more like a shaggy carpet.

Why does your body need all this extra surface area? Because villi are where nutrients actually enter your bloodstream. When you eat a sandwich, your stomach and intestines break it down into molecules small enough to pass through the walls of these villi into your blood. Without villi, your intestinal walls would be smooth, and you'd absorb only a fraction of the nutrients from your food.

Each villus is covered in even tinier projections called microvilli, multiplying the surface area even more. If you could somehow flatten out all the villi and microvilli in your small intestine, they'd cover an area about the size of a tennis court, all folded up inside your belly.

Scientists who study digestion, nutrition, and diseases of the intestine pay close attention to villi. In certain conditions, villi can become damaged, making it hard for people to absorb nutrients properly. Healthy villi are essential for turning the food you eat into energy and building blocks your body can actually use.