MEPX
Chapter 5 of 14All chapters
  1. 1How the body is organised
  2. 2Cells and tissues
  3. 3The skeleton
  4. 4Muscles
  5. 5Heart and circulation
  6. 6Blood
  7. 7Lungs and breathing
  8. 8Digestion
  9. 9Kidneys and liver
  10. 10The nervous system
  11. 11The brain
  12. 12Hormones
  13. 13Skin and senses
  14. 14The immune system

Chapter 5 of 14

Heart and circulation

The pump and its two circuits.

Two loops

The heart pumps blood through the lungs to collect oxygen, then out to the rest of the body. Four chambers keep the two circuits separate so oxygen rich and oxygen poor blood never mix.

  • Roughly 100,000 beats a day, without instruction from the brain.
  • Arteries carry blood away from the heart and veins bring it back.

Blood pressure

The two numbers are the pressure while the heart contracts and while it rests between beats. Vessels narrow and widen constantly to keep supply matched to demand.