More exchange surfaces

• Haemoglobin


  To carry oxygen round the body
• Haemoglobin


  • 4 polypeptide chains
  • Each chain has a Haem group which carries oxygen
• Oxyhaemoglobin


  When oxygen joins with haemoglobin
• Affinity for oxygen


  The tendency a molecule has to bind with oxygen
• Haemoglobin can associate with 4 oxygen molecules
• Low partial pressure of Oxygen


  In active tissues e.g. muscle, oxygen dissociates from haemoglobin and is released into the cells so they can respire
• High partial pressure of Oxygen


  In the lungs, oxygen associates with haemoglobin to be carried round the body
• As partial pressure increases

  Haemoglobins affinity for oxygen increases
• Oxygen dissociation curve


  An S-shape curve, when haemoglobin binds with the first oxygen molecule, there is an allosteric change so that the 2nd, 3rd and 4th oxygen molecules are taken up at an increasing rate. But as the haemoglobin becomes saturated it becomes harder for oxygen to be taken up, so the graph levels out.
• Bohr shift


  A shift to the right of an oxygen dissociation graph due to high partial pressure of carbon dioxide or low pH
• Oxygen dissociation curve shifting left

  Haemoglobin has a higher affinity for oxygen, more oxygen associates with Hb more readily, e.g. in organisms in low oxygen environments
• Oxygen dissociation curve shifting right

  Haemoglobin has a lower affinity for oxygen, more oxygen dissociates from Hb more readily, e.g. in organisms with high rates of respiration
• The heart has four chambers
• Coronary arteries


  They are arteries that supply the heart with blood, the heart is constantly contracting meaning it needs energy to do so, oxygen and glucose is needed for respiration for energy
• Atrioventricular valves


  Prevent back flow of blood
• The left ventricle has a thicker wall to allow for oxygenated blood to flow at a higher pressure
• Closed double circulatory system

  Blood passes through the heart twice per complete circuit through the body
• Risk factors for cardiovascular disease

  • Poor diet/Obesity
  • Smoking
  • High blood pressure
  • Genetics
• Myocardial infarction


  If a coronary artery becomes blocked an area of the heart muscle will be cut off from its blood supply receiving no oxygen
• Diastole


  Relaxation of heart muscles
• Factors affecting pressure


  • Volume of blood
  • The volume of the chamber itself (this can be decreased through the contraction of the cardiac muscle)
• Valves opening and closing

  1. They open when the pressure is greater behind the valve

  2. They close when pressure is greater in front of valve
• What happens during diastole/relaxation

  1. Atria and ventricles relaxed

  2. Blood enters atria

  3. As vol of blood in atria increases, the pressure in atria exceeds the pressure in ventricles

  4. Atrioventricular valves open blood flows into ventricles

  5. Semi lunar valves closed
• What happens during atrial systole

  1. Atria contract, increasing pressure even more and pushing blood into the ventricles

  2. Ventricles remain relaxed

  3. AV valves open

  4. Semi lunar closed
• What happens during ventricular systole

  1. Atria relax, ventricles contract

  2. Blood pressure in ventricles rises and exceeds atria

  3. AV valve close

  4. Semilunar valves open and blood is forced into arteries
• Artery


  Carry blood away from heart to rest of the body at high pressure
• Arteries


  • Walls are thick and muscular and have elastic tissue to stretch and recoil - helps maintain high pressure
  • Endothelium is folded allowing artery stretch - maintain high pressure
  • All arteries carry oxygenated blood apart from pulmonary artery which take deoxygenated blood to lungs
• Arterioles


  Arteries divide into smaller vessels called arterioles
• Veins


  • Wider lumen with very little elastic or muscle tissue
  • Contain valves to prevent backflow of blood
  • All veins carry deoxygenated blood except from pulmonary vein which carry oxygenated blood from lungs to heart
• Capillaries


  Where substances are exchanged between cells and blood
• Capillaries


  • Found very near cells in exchange tissues - short diffusion pathway
  • Walls are one cell thick - short diffusion pathway
  • Large number - large surface area for exchange
• Tissue fluid


  The liquid that surrounds cells allowing for transport between the blood and cells via diffusion
• How tissue fluid is formed

  At the start of the capillary bed, nearest the arteries, the hydrostatic pressure inside the capillaries is greater than in the tissue fluid. This difference in hydrostatic pressure means an overall outward pressure forces fluid out of capillaries and into spaces around cells
• Role of the heart in the formation of tissue fluid

  Contractions of left ventricle creates hydrostatic pressure which forces fluid out of capillaries
• Why some water re-enters the capillaries from the tissue fluid at the venule end

  Due to fluid loss and an increasing concentration of plasma proteins, the water potential at the venule end of capillary bed is lower than the water potential in the tissue fluid. Water moves down the water potential gradient and into capillaries
• Excess tissue fluid


  Drained into lymphatic system, which transports fluid from tissues and passes it back to circulatory system
• How net fluid movement changes along the capillary

  Hydrostatic pressure is much greater at the arteriole end than at the venule end
• Xylem


  Transports water and mineral ions up the plant from roots to leaves
• Xylem


  • Long, tube-like structures formed from dead cells joined end to end. No end walls between cells making an uninterrupted tube that allows water to pass up tube easily
• Transpiration


  The loss of water vapour from a plant through the stomata in the leaf