Circulatory system

notes on the heart, blood vessels, blood etc.

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Different types of blood vessel


  • thick walled
  • blood under high pressure
  • no valves
  • carries blood away from heart
  • small passageway for blood
  • elastic - expands to carry blood
  • carries oxygenated blood except for the PULMONARY ARTERY


  • thin walled
  • blood under low pressure
  • valves (to prevent backflow of blood)
  • carries blood towards heart
  • large passageway for blood
  • non-elastic
  • carries deoxygenated blood except for the PULMONARY VEIN
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What are they like?

  • microscopic blood vessels linking arterioles and venules
  • extremely thin walls (1 cell thick)
  • allow food and oxygen to pass out to our body tissues
  • allow carbon dioxide and other waste to pass into blood from body tissues

What do they do?

1) arterioles bring oxygen and nutrients to the capillaries

2) the oxygen and nutrients squeeze out through the thin capillary walls in muscle tissue

3) as muscle contracts, it produces waste products,eg carbon dioxide. this squeezes back into the capillary

4) capillary joins up with venules which lead to veins and back to heart. carbon dioxide is then removed by our lungs. other waste is removed by kidneys

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What is it made of?

  • red blood cells - give blood its colour, contains haemoglobin (which carries O2 from lungs to body)
  • white blood cells - deal with infection and disease by producing antibodies or engulfing germs
  • Platelets - made in bone marrow, produce clots when a blood vessel is damaged
  • Plasma - contains waste eg salts, calcium, glucose, hormones, CO2

What does blood do?

  • Transportation - carries nutrients from digestive system to body cells, takes oxygen from lungs to muscles, removes waste, carries hormones
  • Protection - carries white blood cells to sites of infection, carries antibodies to destroy germs, carries platelets to damaged areas
  • Temperature regulation - maintains temp within body by carrying heat away from working muscles to skin AND carrying heat from centre of body to skin
  • Maintains body balance - reduces effect of lactic acid, regulates fluid balance, anables hormones and enzymes to work
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3 stages of heart action:

stage 1 - when heart is relaxed between beats, blood flows into it. deoxygenated blood from body enters right atrium through superior and inferior vena cava. AT THE SAME TIME newly oxygenated blood from lungs enters left atrium through the pulmonary veins

stage 2 - muscles in right atrium contract to pump blood through the tricuspid valve into right ventricle. AT THE SAME TIME muscles in the left atrium contract to pump blood throughbicuspid valve into the left ventricle

stage 3 - muscles in right ventricle contract to pump blood through semilunar valves into pulmonary artery to travel to the lungs. muscles in left ventricle contract to pump blood through the semilunar valves into aorta, to travel around body again.

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