← The Human Body

Chapter 3

Heart, blood and breath

Every breath brings oxygen into the lungs, where it passes into the blood. The heart, a muscle the size of a fist, pumps that blood through arteries, capillaries and veins to every cell, and back again. At rest, the whole round trip takes about a minute. During exercise, the heart beats faster and harder and you breathe more deeply, so your muscles get the extra oxygen they need.

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  1. Number of chambers in the human heart4
  2. Normal adult resting heart rate, in beats a minute60 to 100
  3. Vessels that carry blood away from the heartArteries
  4. Tiny vessels where oxygen passes into the bodyCapillaries
  5. Protein in red blood cells that carries oxygenHaemoglobin
  6. Blood cells that help stop bleedingPlatelets
  7. Blood cells that fight infectionWhite blood cells
  8. How much blood an average adult hasAbout 5 litres
  9. Tiny air sacs in the lungsAlveoli
  10. The muscle under the lungs that drives breathingDiaphragm