circulatory system

• the heart has four chambers, two atria (top) and two ventricles (bottom)
• Substance transported


  1. From lungs to all cells

  2. From digestive system to liver

  3. From lungs to lungs
• Their volume increases


  Diffusion is not quick enough to move substances to where they're needed in the organism's body
• Effectiveness of exchange surfaces in plants and animals

  • Large surface area
  • Short distance required for diffusion
• Structures with large surface area

  • Alveoli in respiratory system
  • Flattened shape of leaves
• Structures with short diffusion distance

  • Walls of blood capillaries are one cell thick
• Their surface area does not increase as fast as their volume
• Benefits of double circulation

  • More efficient
  • Maintains higher pressure
  • Only one blood flow in mammals vs two in other animals
  • 4 chambers vs 2 chambers
  • Needs more energy
  • Lower surface area to volume ratio
• Mammals need a double circulation as it maintains higher pressure / faster flow than a single circulatory system, mammals need a greater supply of oxygen as they're warm blooded
• Blood passes through the heart twice in one circuit
• Blood is pumped around the body by the heart
• Circulatory system: HEALTH
• The Heart


  Has two ventricles and two atria, which receive blood from veins and pump it into arteries
• Journey of blood through the heart

  1. Blood enters right atrium

  2. Flows into right ventricle

  3. Pumped into pulmonary artery

  4. Oxygenated in lungs

  5. Returns to left atrium

  6. Flows into left ventricle

  7. Pumped into aorta
• Heart chambers


  • Right atrium
  • Right ventricle
  • Left atrium
  • Left ventricle
• Heart valves


  • Tricuspid valve
  • Bicuspid valve
  • Semilunar valves
• Atrium has a higher pressure than ventricle
• Blood vessels


  • Arteries (thick, muscular walls, carry blood away from heart at high pressure)
  • Veins (thinner walls, carry blood towards heart at low pressure)
  • Capillaries (very thin, one cell thick, allow exchange of gases and nutrients)
• Aorta is the largest artery, has thick muscular walls to withstand high blood pressure
• Blood vessel walls are semi-permeable to allow transport of substances
• Red blood cells transport oxygen, white blood cells fight infection, platelets clot to prevent blood loss
• Plasma is the liquid part of blood
• de-oxygenated blood comes back into the heart via the pulmonary vein
• oxygenated blood goes into the pulmonary artery which carries it to the lungs where carbon dioxide diffuses out and oxygen diffuses in
• blood is pumped from the right side to the left
• Oxygenated blood leaves the heart through the aorta
• the right atrium receives de-oxygenated blood from the body through the superior vena cava and inferior vena cava