Mass transport in animals

• Describe the role of red blood cells and haemoglobin in oxygen transport.

  • RCB's contain lots of haemoglobin (Hb) - no nucleus, biconcave, high SA:V, short diffusion pathway
  • Hb associates/loads O2 at gas exchange surfaces where partial pressure of O2 (pO20 is high
  • This forms oxyhaemoglobin which transports O2 (each can carry 4O2 - one at each Haem group)
  • Hb dissociates from/unloads O2 near cells/tissues where pO2 is low
• Describe the structure of Haemoglobin

  • Protein with a quaternary structure
  • Made of 4 polypeptide chains
  • Each chain contains a Haem group containing an iron ion (Fe2+)
• Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve

  Areas with low pO2 (respiring tissue):

  • Hb has a low affinity for O2
  • So O2 readily unloads/dissociates with Hb
  • So % saturation is low

  Areas with high pO2 (gas exchange surfaces):

  • Hb has a high affinity for O2
  • So O2 readily loads/associates with Hb
  • So % saturation is high
• Explain how the cooperative nature of oxygen binding results in an S-shaped (sigmoid) oxyhaemoglobin dissociation curve

  1. Binding of first oxygen changes tertiary/quaternary structure of Hb
  2. This uncovers Haem group binding sites, making further binding of oxygens easier
• What is the Bohr effect?

  Effect of CO2 concentration on dissociation of oxyhaemoglobin -> curve shifts to the right
• Explain the effect of CO2 concentration on the dissociation of oxyhaemoglobin

  1. Increasing blood CO2 e.g. due to increased rate of respiration
  2. Lowers blood PH (more acidic)
  3. Reducing Hb's affinity for oxygen as tertiary/quaternary structure changes slightly
  4. So more/faster unloading of oxygen to respiring cells at a given pO2
• Explain the advantage of the Bohr effect (e.g. during exercise)

  More dissociation of O2 -> faster aerobic respiration/less anaerobic respiration -> more ATP produced
• Explain how organisms can be adapted to their environment by having different types of haemoglobin with different O2 transport properties

  Curve shift left -> Hb has a higher affinity for O2

  • More O2 associates with Hb more readily
  • At gas exchange surfaces where pO2 is lower
  • E.g. organisms in low O2 environments - high altitudes, underground, foetuses

  Curve shift right -> Hb has a lower affinity for O2

  • More O2 dissociates from Hb more readily
  • At respiring tissues where more O2 is needed
  • E.g. organisms with high rates of respiration/metabolic rate (may be small or active)
• Suggest the importance of a double circulatory system

  Prevents mixing of oxygenated/deoxygenated blood

  • So blood pumped to body is fully saturated with oxygen for aerobic respiration

  Blood can be pumped to body at a higher pressure

  • Substances taken to/removed from body cells quicker/more efficiently
• Atrial Systole

  • Atria contract -> volume decreases, pressure increases
  • Atrioventricular valves open when pressure in atria exceeds pressure in ventricles
  • Semilunar valves remain shut as pressure in arteries exceeds pressure in ventricles
  • So blood pushed into ventricles
• Ventricular Systole

  • Ventricles contract -> volume decreases, pressure increases
  • Atrioventricular valves shut when pressure in ventricles exceeds pressure in atria
  • Semilunar valves open when pressure in ventricles exceeds pressure in arteries
  • So blood pushed out of heart through arteries
• Diastole

  • Atria and ventricles relax -> volume increases, pressure decreases
  • semilunar valves shut when pressure in arteries exceeds pressure in ventricles
  • Atrioventricular valves open when pressure in atria exceeds pressure in ventricles
  • So blood fills atria via veins and flows passively into ventricles
• Explain how the structure of arteries relates to their function

  • Thick smooth muscle tissue -> can contract and control/maintain blood flow/pressure
  • Thick elastic tissue -> can stretch as ventricles contract and recoil as ventricles relax, to reduce pressure surges/maintain high pressure
  • Thick wall -> withstand high pressure/stop bursting
  • Smooth/folded endothelium - reduces friction/can stretch
  • Narrow lumen -> increases/maintains high pressure
• What is the function of Arterioles?

  Direct blood to different capillaries/tissues
• Explain how the structure of arterioles relates to their function

  1)Thicker smooth muscle than arteries

  • Contracts -> narrows lumen (vasoconstriction) -> reduces blood flow to capillaries
  • Relaxes -> widens lumen (vasodilation) -> increases blood flow to capillaries

  2)Thinner elastic layer -> pressure surges are lower (as further from heart/ventricles)
• Explain how the structure of veins relates to their function

  • Wider lumen than arteries -> less resistance to blood flow
  • Very little elastic and muscle tissue -> blood pressure lower
  • Valves -> prevent backflow of blood
• Explain how the structure of capillaries relates to their function

  • Wall is a thin (1 cell) layer of endothelial cells -> reduces diffusion pathway
  • Capillary bed is a large network of branched capillaries -> increases SA or diffusion
  • Small diameter/narrow lumen -> reduces blood flow rate so more time for diffusion
  • Pores (fenestrations) in walls between cells -> allows larger substances through
• Explain the formation of tissue fluid- Arteriole end of capillaries

  1)Higher blood/hydrostatic pressure inside capillaries than tissue fluid

  2)Forcing water and dissolved substances out of capillaries

  3)Large plasma proteins remain in capillary
• Explain the return of tissue fluid to the circulatory system - Venule end of capillaries

  1)Hydrostatic pressure reduces as fluid leaves capillary

  2)(due to water loss) an increasing concentration of plasma proteins lowers water potential in capillaries below that of tissue fluid

  3)Water enters capillaries from tissue fluid by osmosis down a water potential gradient

  4)Excess water taken up by lymph capillaries and returned to circulatory system through veins.
• Suggest and explain causes of excess tissue fluid accumulation

  1)Low concentration of protein in blood plasma OR high salt concentration

  • Water potential in capillary not as low -> water potential gradient is reduced
  • So more tissue fluid is formed at arteriole end/less water absorbed at venule end by osmosis

  2)High blood pressure -> high hydrostatic pressure

  • Increases outward pressure from arterial end AND reduces inward pressure at venule end
  • So more tissue fluid formed at arteriole end/less water absorbed at venule end by osmosis
  • Lymph system may not be able to drain excess fast enough
• What is the equation for cardiac output?

  Cardiac output = Stroke volume x Heart rate

  
  

  • Cardiac Output = volume of blood pumped out of the heart per min
  • Stroke Volume = volume of blood pumped in each heartbeat
  • Heart Rate = number of beats per minute
• How can heart rate be calculated from cardiac cycle data?

  Heart Rate = 60s/length of one cardiac cycle in seconds
• Explain why different types of haemoglobin can have different oxygen transport properties:

  • Different types of Hb are made of polypeptide chains with slightly different amino acid sequences
  • Resulting in different tertiary/quaternary structures = different affinities for oxygen