The small intestine: where your food finally gets into your body

Squirt by squirt, the soup enters your small intestine. It is a narrow tube about five metres long, folded up in your belly. Most of the cutting happens here.

First, a gland behind your stomach pours in its juice. This gland is the pancreas. Its juice is full of enzymes for every kind of food: starch, protein and fat. It also calms the acid from the stomach.

Fat is harder to cut. It does not mix with the watery soup, so it stays in big drops. So your liver sends a juice called bile. Bile works like dish soap: it breaks the big drops into tiny ones, and the enzymes can reach them.

Little by little, the chains of your lunch fall apart into single pieces: sugars, amino acids and small pieces of fat. Now they are small enough to cross the wall.

And the wall is built for this. It has big folds. The folds are covered in tiny fingers called villi. And each cell on a finger is covered in even tinier bumps, like the hairs of a brush.

Spread flat, all that wall would cover about 30 square metres, about half a badminton court. Old schoolbooks said a tennis court. In 2014, scientists counted again, more carefully, and found less. Still, it is a lot of wall for one tube.

On this huge wall, the pieces cross into tiny vessels inside each finger. At last, your lunch is inside your body. The sugars go straight into your blood, and the sugar in your blood goes up: your blood sugar rises.

But here is a puzzle. All the sugar in your blood, at any moment, is about one teaspoon. The starch of your bowl makes about 15 teaspoons of sugar, and it is pouring in. Where does it all go?