The circulatory system

• Artery


  From heart to body

  Walls have thick and muscular tissue and elastic tissue to stretch and recoil - helps maintain high pressure

  Endothelium folded, allowing artery to stretch - helps maintain high pressure
• Arterioles 


  Divided from arteries

  Form network through body
• Veins


  Back to heart, low pressure

  Wider lumen than arteries with very little elastic or muscle tissue

  Contain valves to stop back flow

  Blood flow helped by contraction of muscles around them
• Capillary


  Found very near cells in exchange tissue - short diffusion pathway

  One cell thick walls

  Large number of capillaries / capillary beds - increase surface area
• Left ventricle of heart is more muscular and thicker than the right as it contracts to send blood around the whole body. When the right has to only send it to the lungs.
• Atrioventricular valves stop blood flowing back into the atria when ventricles contract
• Semi lunar valve, stops blood flowing back into the heart after the ventricles contract
• High pressure behind a vale - open

  High pressure in front a valve - closed
• Order of heart movements for pumping

  Atrial systole

  Ventricular systole

  Diastole
• Atrial systole


  Ventricles relaxed, atria contract

  Decreasing volume of chambers increasing pressure in chambers

  Pushes blood into ventricles

  Increase in ventricular pressure and chamber volume
• Ventricle systole


  Atria relax, ventricles contract

  Decreasing volume increasing pressure

  Pressure higher in ventricles than atria, forces atrioventricular valves to shut to prevent back flow

  Pressure higher in ventricles than aorta and pulmonary artery forcing open the semi lunar valves
• Diastole


  Ventricles and atria both relax

  Higher pressure in aorta and artery closes semi lunar valves ti prevent back flow to ventricles

  Blood returns to atria due to high pressure in vena cava and pulmonary vein

  Increase pressure atria, ventricles relax atrioventricular valves open

  Blood flows to ventricles from atria, atria contract