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← 🫀 Human body · usually met in Std 6-12

The heart and circulation

A four-chambered pump that sends blood on two circuits: a short one to the lungs for oxygen, and a long one to the rest of the body.

LUNGS right atrium right ventricle left atrium left ventricle thickest wall THE BODY oxygen used, CO₂ picked up back from the body, low in oxygen out to the body Blue = low in oxygen · Red = oxygen-rich. Valves between the chambers stop it going backwards — that is the heartbeat you hear.
Drawn for Star Student.

Blood low in oxygen arrives at the right atrium, drops into the right ventricle and is pumped to the lungs. It returns oxygen-rich to the left atrium, drops into the left ventricle, and is pumped out to the body. Valves between the chambers stop it going backwards — the two sounds of a heartbeat are those valves closing. The left ventricle has the thickest wall, because its circuit is the whole body and the right one is only the lungs.

Arteries carry blood away from the heart under pressure and have thick elastic walls. Veins bring it back at lower pressure and have valves to stop it pooling in the legs. Between them, capillaries are a single cell thick, which is the entire point: the exchange of oxygen, nutrients and waste can only happen across a wall that thin.

Worth knowing

  • A resting adult heart beats roughly 60-100 times a minute and does not get a day off.
  • The heart has its own blood supply, the coronary arteries; a blockage in one is what a heart attack is.
  • Total length of the blood vessels in one adult body runs to tens of thousands of kilometres, nearly all of it capillaries.

Want to see it moving? Search YouTube for “The heart and circulation” ↗ — we send you to the search rather than to one video, because a link to one video eventually rots.

See also

🌱 Respiration🫀 The lungs and breathing🫀 Blood

🧭 Do not take our word for it

This entry was written for Star Student in our own words — it is a summary, not a source. Here is where the people who actually hold these facts keep them. Go and check.

Your own textbook ↗Balbharati publishes the textbooks free to read online. Your chapter is the thing to check first — an encyclopedia is a summary, and the syllabus is the syllabus. World Health Organization ↗Health facts stated carefully, and updated when the evidence changes.

Last gone through: 1 October 2026 · How these entries are written

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