The heart and the journey of the blood
Aprende
The heart is a muscle the size of your fist. It is in the middle of the chest, a little to the left. It works like a pump: it contracts and pushes the blood; then it relaxes and fills up again. Each contraction is a heartbeat. At rest, a child has between 70 and 100 beats per minute. The heart never stops, not even when you sleep.
The heart, between the two lungs One heartbeat: the heart contracts and relaxes Each heartbeat pushes the blood along tubes called blood vessels. You can feel that push as a little tap on your wrist or neck: it is your pulse. If you count the beats in 15 seconds and multiply by 4, you know how many you have in a minute. With exercise, the heart beats faster. When you rest, it calms down again.
Blood is a red liquid that delivers what each part of the body needs. It carries oxygen, which it takes in at the lungs, and nutrients, which it takes in at the intestine when you digest your food. It also collects what is left over: carbon dioxide and other waste.
carries leaves from arrives at oxygen lungs whole body nutrients intestine whole body CO₂ whole body lungs What the blood carries Blood is not used up: it circulates. It leaves the heart, goes round the body and returns to the heart, over and over again. When it comes back, it brings little oxygen and a lot of carbon dioxide. The heart sends it to the lungs, where it gives off the carbon dioxide and takes in new oxygen. Then it sends it round the whole body again.
The journey of the blood, in short
Worked examples
Ejemplo 1
Gus takes his pulse sitting down and counts 19 beats in 15 seconds. How many beats per minute does he have? Is that normal at rest?
| time | beats |
|---|---|
| 15 seconds | 19 |
| 1 minute | ? |
- A minute is 4 times 15 seconds.
- Multiply by 4: 19 × 4 = 76.
- A child at rest has between 70 and 100 beats per minute, and 76 is in that range.
He has 76 beats per minute, and that is normal at rest.
¡Ojo! Here many children stop at 19, which is the beats in 15 seconds, not in a minute.
Ejemplo 2
Tony cycles fast to the canal. When he gets there, he notices that his heart is beating very fast. Why?
- When he cycles, his muscles work harder.
- They need more oxygen and more nutrients.
- The heart pushes more blood per minute, and to do that it beats faster.
The heart beats faster to carry more oxygen and nutrients to the muscles.
¡Ojo! Here many children think that the heart is frightened or tired, and not that it is carrying more blood.
Ejemplo 3
Ellie bakes bread and Julie eats a piece. After she digests it, how do its nutrients reach Julie’s muscles?
- The bread is digested in the stomach and in the intestine.
- The nutrients pass from the intestine into the blood.
- The blood, pushed by the heart, carries them to the whole body, to the muscles too.
The blood delivers the nutrients of the bread to the whole body.
¡Ojo! Here many children think that nutrients go straight from the stomach to the muscles, without going through the blood.
Un reto para pensar
Measure your pulse sitting down: count the beats in 15 seconds and multiply by 4. Then draw a picture with the heart, one arrow going out to the body and another coming back. Write above each arrow what the blood carries.
Practica
Rondas de 10 preguntas. Elige el nivel:
Next topic: Experiment: measuring your pulse before and after exercise →