Animal Transport

• Diastole

  • Ventricles and atria relax
  • semi Luna valves close, atrioventricular valves open
  • wave of excitement is prevented from travelling back up to the atria by non-conductive connective tissue
• Atrial Systole

  • Sinoatrial node (SAN) releases an electrical impulse = wave of excitement
  • this travels through the walls of the atria causing them to contract at the same time
  • Atrioventricular valves stay open and Semi Luna valves stay closed
• Ventricular Systole

  • The wave of excitement is held by the atrioventricular node (AVN) = AVN delay
  • this allows the atria to fully contract before ventricles
  • AVN releases WOE
  • WOE travels down the septum through bundle of His to the apex of the heart
  • WOE then travels through Purkyne fibres causing the ventricles to contract from base upwards
  • Atrioventricular valves close and Semi Luna valves open
• structure of capillaries

  • walls are 1 cell thick - endothelial cells
  • the cells are fixed to a basement membrane. There are gaps in the walls called fenestrations
  • They have a narrow lumen which is smaller in diameter of a red blood cell - results in friction between RBC and wall which slows down the velocity of blood flow
  • The capillaries have a large total cross-sectional area
• How do capillaries work (arteriole end)?

  1. arteriole end has high hydrostatic pressure due to contractions of the left ventricle
  2. fluid is forced out of the fenestrations as the hydrostatic pressure is greater then osmotic pressure
  3. tissue fluid is formed containing components such as glucose and amino acids which are taken in by body cells.
• How do capillaries work (venule end)?

  1. Low hydrostatic pressure due to loss of fluid from the blood, increased resistance of flow due to small lumen.
  2. Osmotic pressure has remained the same due to the retention of the large plasma proteins - lower the water potential of blood
  3. Fluid will enter the capillary by osmosis as the osmotic pressure is greater then the hydrostatic pressure - fluid contains CO2, urea and water.
• Problems with high blood pressure

  • High blood pressure = Hypertension
  • hydrostatic pressure is greater then osmotic pressure for longer across the capillary bed
  • less time/distance for reabsorption
  • lymphatic system is overwhelmed
  • this causes swelling
• Problems with Kwashiorkor

  • Lack of protein in the diet
  • lack of large plasma proteins in the blood
  • higher water potential in the blood at the venule end
  • this means HP is greater then OP for longer across capillary bed
  • Less fluid is reabsorbed
• Cooperative binding

  • Haem groups are in the centre of the haemoglobin so it is difficult for oxygen to bind with them - low saturation levels at low partial pressures.
  • Eventually the 1st O2 molecule binds with one haem group and which changes the shape of the haemoglobin molecule, making it easier for the second molecule to attach.
  • 2nd O2 molecule attaches and changes the shape again
  • 3rd O2 molecule attaches but does not induce a shape change
  • 4th O2 molecule attaches only if there is a large increase in ppO2 - very difficult
• oxygen dissociation curve

  • Haemoglobin picks up (associates with) oxygen to form oxyhaemoglobin in tissue with high O2 levels.
  • At low oxygen ppO2 the haemoglobin does not easily load. oxygen Haemoglobin releases O2 (dissociates) in tissue with low O2 levels.
  • s-shaped (sigmoid) due to co-operative binding

  
• foetal haemoglobin

  • Foetal haemoglobin has a slightly different structure to adult haemoglobin and greater affinity for O2 than mother’s haemoglobin at the same ppO2.
  • The percentage saturation of the foetus’s blood is always higher than the mother’s = Shift to the left
• Myoglobin

  • very high affinity for O2
  • Associates O2 at much lower ppO2
  • Only dissociates O2 to the cell to maintain aerobic respiration for longer
• Advantages and Disadvantages of shift to the left - O2 dissociation curves

  Advantages:

  • Associate O2 onto the Hb at lower ppO2 e.g. foetal Hb

  Disadvantages:

  • O2 is harder to dissociate at the body tissues
  • need very low ppO2 to dissociate O2
  • Less O2 for aerobic respiration
• Bohr shift - part 1

  • Carbon dioxide diffuses into the red blood cell
  • the carbon dioxide reacts with water in the presence of the enzyme carbonic anhydrase
  • Carbonic acid is formed which splits into a hydrogen ion and a hydrogen carbonate ion
  • The hydrogen carbonate ions exit the RBC into the plasma so chloride ions enter the RBC in a 1:1 ratio to maintain electrochemical neutrality
• Bohr Shift - part 2

  • The hydrogen ions will bind to the haemoglobin and dissociate the oxygen as it has a higher affinity for haemoglobin
  • This forms haemoglobonic acid
  • This means more oxygen is supplied to the respiring tissues that need more oxygen for aerobic respiration
  • This means the oxygen dissociation curve will shift to the right - Bohr shift