Learn · Science · Class 6

Circulatory System

The heart, the blood and the vessels that carry it everywhere.

10 parts
Scroll to begin ↓
The heart pumps blood on two journeysHEART(a pump)LUNGSpicks up oxygenBODYdelivers oxygenArteries carry blood AWAY · Veins carry it BACKCapillaries are the tiny vessels where the swap happens.
Blood goes heart → lungs → heart → body → heart.
🧩 The partsThe heartPart 2 of 10
🔍 In detailArteries, veins and capillariesPart 3 of 10
✏️ Worked exampleWhat blood carriesPart 4 of 10
🌍 In the real worldThe double journeyPart 5 of 10
🔍 In detailPulse and exercisePart 6 of 10
🌍 In the real worldLooking after your heartPart 7 of 10
⚠️ Common mistakesWhere marks goPart 8 of 10
✅ SummaryWhat to rememberPart 9 of 10
✏️ Worked exampleWatch one worked throughPart 10 of 10
1📘 DefinitionPart 1 / 10

A transport system

The circulatory system carries oxygen, water and nutrients to every cell, and takes waste away.

It has three parts: the heart (a pump), the blood (the cargo) and the blood vessels (the roads).

Check yourself: What are the three parts of the circulatory system?
2🧩 The partsPart 2 / 10

The heart

The heart is a muscle about the size of your fist, sitting in the middle of the chest and tilted slightly left.

It beats about 70 times a minute at rest, and never stops for your whole life.

Check yourself: The heart is made mostly of…
3🔍 In detailPart 3 / 10

Arteries, veins and capillaries

Arteries carry blood away from the heart. They have thick walls because the blood is at high pressure.

Veins carry blood back to the heart, at lower pressure, and have valves to stop it flowing backwards.

Capillaries are only one cell thick, thin enough for substances to pass through.

Check yourself: Which vessels carry blood away from the heart?
4✏️ Worked examplePart 4 / 10

What blood carries

Red blood cells carry oxygen. White blood cells fight infection.

Plasma is the liquid that carries everything else, nutrients, waste and heat.

Check yourself: Which blood cells carry oxygen?
5🌍 In the real worldPart 5 / 10

The double journey

Blood makes two trips through the heart on each full circuit.

Heart → lungs (collect oxygen) → back to heart → body (deliver oxygen) → back to heart. That is why it is called double circulation.

Check yourself: Where does blood go straight after leaving the heart the first time?
6🔍 In detailPart 6 / 10

Pulse and exercise

Your pulse is the surge of blood pushed along an artery each time the heart beats. Feel it at the wrist or neck.

During exercise muscles need more oxygen, so the heart beats faster and harder. Afterwards the rate slowly returns to normal.

Check yourself: Why does your pulse rate rise during exercise?
7🌍 In the real worldPart 7 / 10

Looking after your heart

The heart is a muscle, so exercise strengthens it. A stronger heart pumps more blood per beat and can beat more slowly at rest.

Smoking and a diet very high in fat both damage blood vessels over time.

Check yourself: A fitter person usually has a resting pulse that is…
8⚠️ Common mistakesPart 8 / 10

Where marks go

  • "Arteries carry oxygen, veins carry carbon dioxide." Not quite, the pulmonary artery carries deoxygenated blood. Arteries are defined by direction, not content.
  • "Blood is blue in veins." It is always red; darker when it carries less oxygen.
  • "The heart is on the left." It is roughly central, tilted left.
9✅ SummaryPart 9 / 10

What to remember

  • Heart (pump) + blood (cargo) + vessels (roads).
  • Arteries carry blood Away; veins bring it back; capillaries allow the swap.
  • Red cells carry oxygen; white cells fight infection; plasma carries the rest.
  • Double circulation: two trips through the heart per circuit.
10✏️ Worked examplePart 10 / 10

Watch one worked through

Here is one done slowly, with the reason for every move. Then one for you.

Watch one first

Trace a red blood cell from the lungs all the way back to the lungs again, naming each chamber.

  1. From the lungs the blood is oxygenated and enters the left side.
    lungs → left atrium
    Left side carries oxygenated blood, right side carries deoxygenated. Fixing that one fact makes the whole path follow.
  2. It drops into the chamber below, then is pumped out to the body.
    left atrium → left ventricle → body
    Atria receive, ventricles pump. The left ventricle has the thickest wall because it pushes blood the whole way round.
  3. The body uses the oxygen, and the blood returns to the right side.
    body → right atrium
    The blood is now deoxygenated, which is why it comes back to the right side and not the left.
  4. It drops down and is pumped the short distance to the lungs.
    right atrium → right ventricle → lungs
    Blood passes through the heart twice in one circuit. That is what double circulation means.

Answer: Lungs, left atrium, left ventricle, body, right atrium, right ventricle, lungs

Now you try

Which chamber pumps blood to the whole body? Two words.

Show the answer

left ventricle

Practise Circulatory System

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🧠 7 quizzes on Circulatory System (4 easy, 2 medium, 1 hard)

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🖨️ Printable worksheet

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