Bread into blood

About this video

You eat a piece of bread with cheese, and a few hours later some of it is fuelling the muscles of your legs. Your fingers are not made of bread, so what happened on the way? This video follows a bite through the digestive system.

Food is made of big, complicated pieces: starch, proteins and fats. They are far too big to get into the blood. Digestion is breaking them down into small, simple pieces that can. It happens in two ways: by squashing and mixing, as the teeth chew and the stomach churns; and by chemicals, the enzymes in digestive juices, which cut big pieces into small ones. Saliva already starts breaking down starch in the mouth.

The digestive system is one long tube. A bite goes from the mouth, where it is chewed, down the oesophagus, the food pipe, to the stomach, which makes acid and enzymes and churns the food. Then comes the small intestine, which finishes digestion with juices from the liver and pancreas, and the large intestine, which takes back water and turns what is left into waste.

The small intestine is small only in width: in an adult it is over 6 metres long, about as long as a bus, and it does most of the digesting, not the stomach. Its wall is covered in tiny finger-shaped bumps called villi, which give it a huge surface. Small pieces of food pass through the thin wall of each villus into tiny blood vessels inside it, and the blood carries them all over the body. This is absorption. This video goes with the lesson Digestion in Biology Level 1 on Knaph.

Transcript

1. 0:00Bread and cheese, a few hours later, fuel your legs. But your fingers are not made of bread. What happened?
2. 0:09Food is made of big pieces, too big to get into your blood. Digestion breaks them small, by chewing and churning, and with enzymes that cut them up.
3. 0:22Follow one bite. The mouth chews it. The food pipe squeezes it down to the stomach, which churns it with acid and enzymes. The small intestine finishes the job, and the large intestine takes back water.
4. 0:46The small intestine is small only in width. It is over six metres long, about a bus, and it does most of the digesting.
5. 0:58Its wall is covered in tiny fingers called villi. Small pieces of food pass through their thin walls into the blood. That is absorption.
6. 1:12Digestion breaks food small enough to get into your blood.