The journey of food: the digestive system
Aprende
When you eat, the food makes a journey through a long tube that goes from the mouth to the anus: the gut, or digestive tract. On this journey the food is digested. To digest is to break food down into pieces so tiny that they pass into the blood. That is how the body uses the nutrients.
The digestive system In the mouth, the teeth crush the food and the saliva moistens it. The tongue moves the mouthful and pushes it when you swallow. Then the mouthful goes down the oesophagus, a tube with muscles that push it towards the stomach. It does not fall because of its weight: that is why it reaches the stomach even if you drink with your head lower, like a horse does.
The stomach is a bag of muscle. It churns the food and mixes it with the gastric juice, which contains acid and starts to break down the proteins. A thick liquid comes out: the chyme.
The journey of food From the stomach, the thick liquid passes into the small intestine, the longest organ of the gut: it is between 6 and 7 metres long, although it is narrow. There digestion finishes and the nutrients pass into the blood. The liver and the pancreas help: they make juices that reach the intestine through small tubes. But the food does not pass through them.
What could not be digested, such as fibre, goes on to the large intestine. It is wider, but shorter: it is about 1.5 metres long. It absorbs the water that is left, and many useful bacteria live in it: the gut microbiota. What is left forms the faeces, which leave through the anus.
How long each organ is (approximate)
Worked examples
Ejemplo 1
Julie eats a piece of Ellie’s bread. Which organs does the bread pass through and what happens to it in each one?
- In the mouth the teeth crush it and the saliva moistens it.
- It goes down the oesophagus and reaches the stomach, where it mixes with the gastric juice.
- In the small intestine it finishes being digested and its nutrients pass into the blood.
- What is left passes into the large intestine and leaves through the anus.
The bread passes through the mouth, the oesophagus, the stomach, the small intestine, the large intestine and the anus.
¡Ojo! Many children add the liver or the pancreas, but the food does not pass through them.
Ejemplo 2
Tony watches a horse drinking at the canal. It lowers its head to the water, and its stomach is higher than its mouth. How does the water get there?
- The water goes in through the mouth and down the oesophagus.
- The oesophagus has muscles that contract section by section and push what is swallowed.
- They push the water in any position, even upwards.
The water reaches the stomach because the muscles of the oesophagus push it.
¡Ojo! Many children think that food goes down by itself because of its weight.
Ejemplo 3
Mara asks Gus: “Which is longer, the small intestine or the large intestine?”
- Look at the graph: the small intestine is between 6 and 7 metres long.
- The large intestine is about 1.5 metres long.
- It is called “small” because it is narrower, not because it is short.
The small intestine is longer: about four times as long as the large intestine.
¡Ojo! Many children think that the widest organ is also the longest.
Un reto para pensar
Draw a body with its gut and write the name of each organ the food passes through. Then, with a piece of string or thread, measure 6 metres in the living room or in the garden: that is how long your small intestine is, although it fits coiled up inside your tummy.
Practica
Rondas de 10 preguntas. Elige el nivel: