3.4.1 Mass transport in animals

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

  • ● Red blood cells contain lots of haemoglobin (Hb) - no nucleus, biconcave, high SA:V, short diffusion path
  • ● Hb associates with / binds / loads O2at gas exchange surfaces where partial pressure of O2 (pO2) 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+)

  (The haemoglobins are a group of chemically similar molecules found in many different organisms.)

  
• Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve

  • Areas with low pO2 (respiring tissues):
  • ● 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 haemoglobin
  2. This uncovers Haem group binding sites, making further binding of oxygens easier
• Describe evidence for the cooperative nature of oxygen binding

  • ● A low pO2 as oxygen increases there is little / slow increase in % saturation of Hb with oxygen
  • ○ When first oxygen is binding
  • ● At higher pO2, as oxygen increases there is a big / rapid increase in % saturation of Hb with oxygen
  • ○ Showing it has got easier for oxygens to bind
• What is the Bohr effect?

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

  1. Increasing blood CO2 eg. due to increased rate of respiration
  2. Lowers blood pH (more acidic)
  3. Reducing Hb’s affinity for oxygen as shape / tertiary / quaternary structure changes slightly
  4. So more / faster unloading of oxygen to respiring cells at a given pO2

  How the curve provides evidence for this:

  at a given pO2 % saturation of Hb is lower

  
• Explain the advantage of the Bohr effect (eg. during exercise)

  More dissociation of oxygen → faster aerobic respiration / less anaerobic respiration → more ATP produced
• 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 / shape → different affinities for oxygen
• Explain how organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties

  • Curve shift left → Hb has higher affinity for O2
  • ● More O2 associates with Hb more readily
  • ● At gas exchange surfaces where pO2 is lower
  • ● Eg. organisms in low O2 environments - high altitudes, underground, or foetuses
  • Curve shift right → Hb has lower affinity for O2
  • ● More O2 dissociates from Hb more readily
  • ● At respiring tissues where more O2 is needed
  • ● Eg. organisms with high rates of respiration / metabolic rate (may be small or active)

  
• Describe the general pattern of blood circulation in a mammal

  1. Deoxygenated blood in right side of heart pumped to lungs; oxygenated returns to left side
  2. Oxygenated blood in left side of heart pumped to rest of body; deoxygenated returns to right

  Closed double circulatory system - blood passes through heart twice for every circuit around body.
• 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 (after being lower from lungs)
  • ○ Substances taken to / removed from body cells quicker / more efficiently
• Draw a diagram to show the general pattern of blood circulation in a mammal, including the names of key blood vessels

  Picture:

  
• Name the blood vessels entering and leaving the heart and lungs

  Entering heart:

  • Vena cava – transports deoxygenated blood from respiring body tissues → heart

  Entering lungs:

  • Pulmonary artery – transports deoxygenated blood from heart → lungs

  Leaving lungs:

  • Pulmonary vein – transports oxygenated blood from lungs → heart

  Leaving heart:

  • Aorta – transports oxygenated blood from heart → respiring body tissues
• Name the blood vessels entering and leaving the kidneys

  • ● Renal arteries – oxygenated blood → kidneys
  • ● Renal veins – deoxygenated blood to vena cava from kidneys
• Name the the blood vessels that carry oxygenated blood to the heart muscle

  Coronary arteries - located on surface of the heart, branching from aorta
• Label a diagram to show the gross structure of the human heart (inside)

  Picture:

  
• Suggest why the wall of the left ventricle is thicker than that of the right

  • ● Thicker muscle to contract with greater force
  • ● To generate higher pressure to pump blood around entire body
• Explain the pressure & volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional flow of blood - 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
• Explain the pressure & volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional flow of blood - 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
• Explain the pressure & volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional flow of blood - diastole

  ● Atria & 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 & flows passively to ventricles
• Explain how graphs showing pressure or volume changes during the cardiac cycle can be interpreted, eg. to identify when valves are open / closed: part 1 - SL valves

  SL valves closed:

  • Pressure in [named] artery higher than in ventricle
  • To prevent backflow of blood from artery to ventricles

  SL valves open:

  • When pressure in ventricle is higher than in [named] artery
  • So blood flows from ventricle to artery

  
• Explain how graphs showing pressure or volume changes during the cardiac cycle can be interpreted, eg. to identify when valves are open / closed: part 2 - AV valves

  AV valves closed:

  • Pressure in ventricle higher than atrium
  • To prevent backflow of blood from ventricles to atrium

  AV valves open:

  • When pressure in atrium is higher than in ventricle
  • So blood flows from atrium to ventricle

  
• Describe the equation for cardiac output

  Cardiac output (volume of blood pumped out of heart per min) = stroke volume (volume of blood pumped in each heart beat) x heart rate (number of beats per min)
• How can heart rate be calculated from cardiac cycle data?

  Heart rate (beats per minute) = 60 (seconds) / length of one cardiac cycle (seconds)
• 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 / even out blood pressure / maintain high pressure
  • ● Thick wall → withstand high pressure / stop bursting
  • ● Smooth / folded endothelium → reduces friction / can stretch
  • ● Narrow lumen → increases / maintains high pressure
• Function of arteries


  carry blood away from heart at high pressure
• Explain how the structure of arterioles relates to their function

  • ● Thicker smooth muscle layer than arteries
  • ○ Contracts → narrows lumen (vasoconstriction) → reduces blood flow to capillaries
  • ○ Relaxes → widens lumen (vasodilation) → increases blood flow to capillaries
  • ● Thinner elastic layer → pressure surges are lower (as further from heart / ventricles)
• Function of arterioles


  (division of arteries to smaller vessels which can) direct blood to different capillaries / tissues
• 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
• Function of veins


  carry blood back to heart at lower pressure
• Explain how the structure of capillaries relates to their function

  • ● Wall is a thin (one cell) layer of endothelial cells → reduces diffusion distance
  • ● Capillary bed is a large network of branched capillaries → increases surface area for diffusion
  • ● Small diameter / narrow lumen → reduces blood flow rate so more time for diffusion
  • ● Pores in walls between cells → allow larger substances through
• Function of capillaries


  allow efficient exchange of substances between blood and tissue fluid (exchange surface)
• Explain the formation of tissue fluid

  At the arteriole end of capillaries:

  1. Higher blood / hydrostatic pressure inside capillaries (due to contraction of ventricles) than tissue fluid (so net outward force)
  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

  At the venule end of capillaries:

  1. Hydrostatic pressure reduces as fluid leaves capillary (also due to friction)
  2. (Due to water loss) an increasing concentration of plasma proteins lowers water potential in capillary 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 - cause 1: low concentration of protein in blood plasma

  • ● Low concentration of protein in blood plasma
  • ○ Water potential in capillary not as low → water potential gradient is reduced
  • ○ So more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis
• Suggest and explain causes of excess tissue fluid accumulation - cause 2: high blood pressure

  • ● High blood pressure (eg. caused by high salt concentration) → 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 a risk factor? Give examples for cardiovascular disease

  • ● An aspect of a person’s lifestyle or substances in a person’s body / environment
  • ● That have been shown to be linked to an increased rate of disease
  • ● Examples - age, diet high in salt or saturated fat, smoking, lack of exercise, genes

  (The principles of analysis, interpretation and evaluation of data covered in ‘3.2 gas exchange’ also apply here.)
• RP5: Describe precautions that should be followed when performing a dissection

  ● Cover any cuts with a waterproof dressing

  ● When using a scalpel, cut away from body onto a hard surface

  ● When using a scalpel, use a sharp blade

  ● When using a scalpel, carry with blade protected / pointing down

  ● Wear disposable gloves and disinfect hands / wash with soap

  ● Disinfect surfaces / equipment

  ● Safe disposal - put gloves / paper towels / organ in a separate bag / bin to dispose

  ● If poisonous chemicals / toxins involved, work in a well ventilated environment
• RP5: Suggest an ethical consideration when dissecting animals

  ● Morally wrong to kill animals just for dissection

  ● So use animals for dissection that have already been killed (humanely) for meat