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) they have no nucleus, are biconcave, high SA:V, and a short diffusion pathway

  Hb associates with oxygen at gas exchange surfaces where partial pressure of oxygen (po2) is high

  this forms oxyhemoglobin which transports oxygen (each can carry 4o2 one at each haem group)

  Hb dissociates from oxygen near cells 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
• describe the loading, transport and unloading of oxygen in relation to the oxyhemoglobin dissociation curve in areas with low partial pressure of oxygen (respiring tissues)

  Hb has a low affinity for oxygen

  so oxygen readily unloads with Hb

  so percentage saturation is low
• describe the loading, transport and unloading of oxygen in relation to the oxyhemoglobin dissociation curve in areas with high partial pressure of oxygen (gas exchange surfaces)

  Hb has a high affinity for oxygen

  so oxygen readily loads with Hb

  so percentage saturation is high
• explain how the cooperative nature of oxygen binding results in an S-shaped (sigmoid) oxyhemoglobin dissociation curve

  binding of first oxygen changes tertiary/quaternary structure of haemoglobin

  this uncovers haem group binding sites, making further binding of oxygens easier
• describe evidence for the cooperative nature of oxygen binding

  at a low partial pressure of oxygen, as oxygen increases there is slow increase in % saturation of Hb with oxygen, when first oxygen is binding

  at higher partial pressure of oxygen, as oxygen increases there is a rapid increase in % saturation of Hb with oxygen, showing it has got easier for oxygens to bind
• what is the Bohr effect

  effect of carbon dioxide concentration on dissociation of oxyhemoglobin so curve shifts to the right
• explain effect of carbon dioxide concentration on the dissociation of oxyhemoglobin

  increasing blood carbon dioxide e.g due to increased rate of respiration

  lowers blood pH (more acidic)

  reducing Hb's affinity for oxygen as shape (tertiary/quaternary structure) changes slightly

  so more unloading of oxygen to respiring cells at given partial pressure of oxygen
• explain the advantage of the Bohr effect (e.g during exercise)

  more dissociation of oxygen so faster aerobic respiration/less anaerobic respiration so 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 so 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 so Hb has higher affinity for oxygen)

  more oxygen associates with Hb more readily

  at gas exchange surfaces where partial pressure of oxygen is lower

  e.g organisms in low oxygen environments (high altitudes, underground or foetuses)
• explain how organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties (curve shift right so Hb has lower affinity for oxygen)

  more oxygen dissociates from Hb more readily

  at respiring tissue where more oxygen is needed

  e.g organisms with high rates of respiration/metabolic rate (may be small or active)
• describe the general pattern of blood circulation in a mammal

  deoxygenated blood in right side of heart pumped to lungs, oxygenated returns to left side

  oxygenated blood in left side of heart pumped to rest of body, deoxygenated returns to right
• 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 higher pressure (after being lower from lungs) so substances taken to/removed from body cells quicker/more efficiently
• name the blood vessels entering and leaving the heart and lungs

  vena cava - transports deoxygenated blood from respiring body tissues to heart

  pulmonary artery - transports deoxygenated blood from heart to lungs

  pulmonary vein - transports oxygenated blood from lungs to heart

  aorta - transports oxygenated blood from heart to respiring body tissues
• name the blood vessels entering and leaving the kidneys

  renal arteries - oxygenated blood to kidneys

  renal veins - deoxygenated blood to vena cava from kidneys
• name the blood vessels that carry oxygenated blood to the heart muscle 


  coronary arteries - located on surface of the heart, branching from aorta
• structures of the human heart (inside) and order

  vena cava

  right atrium

  atrioventricular valave

  right ventricle

  semilunar valve

  pulmonary artery

  pulmonary vein

  left atrium

  atrioventricular valve

  left ventricle

  semilunar valve

  aorta
• 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
• atrial systole

  atria contact so volume decreases and 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 so volume decreases and 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 and volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional flow of blood (diastole)

  atria and ventricles relax so volume increases and 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 to ventricles
• explain how graphs showing pressure or volume changes during the cardiac cycle can be interpreted (SL valves closed)

  pressure in (named) artery higher than in ventricle

  to prevent back flow of blood from artery to ventricles
• explain how graphs showing pressure or volume changes during the cardiac cycle can be interpreted (SL valves open)

  when pressure in ventricles 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 (AV valves closed)

  pressure in ventricle higher than atrium

  to prevent back flow of blood from ventricles to atrium
• explain how graphs showing pressure or volume changes during the cardiac cycle can be interpreted (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 (number of beats per min) = 60 (seconds)/length of one cardiac cycle (seconds)
• explain how the structure of arteries relates to their function

  function - too carry blood away from heart at high pressure

  thick smooth muscle tissue which can contract and control/maintain blood flow/pressure

  thick elastic tissue which can stretch as ventricles contract and recoil as ventricles relax, to reduce pressure surges/even out blood pressure/maintain high pressure

  thick wall to withstand high pressure/stop bursting

  smooth/folded endothelium so reduces friction/can stretch

  narrow lumen which increases/maintains high pressure
• explain how the structure of arterioles relates to their function

  function - (division of arteries to smaller vessels which can) direct blood to different capillaries/tissues

  thicker smooth muscle layer than arteries

  contracts which narrows lumen (vasoconstriction) so reduces blood flow to capillaries

  relaxes which widens lumen (vasodilation) so increases blood flow to capillaries

  thinner elastic layer so pressure surges are lower (as further from heart/ventricles)
• explain how the structure of veins relates to their function

  function - carry blood back to heart at lower pressure

  wider lumen than arteries so less resistance to blood flow

  very little elastic and muscle tissue so blood pressure lower

  valves to prevent back flow of blood
• explain how the structure of capillaries relates to their function

  function - allow efficient exchange of substances between blood and tissue fluid (exchange surface)

  wall is a thin (one cell) layer of endothelial cells so reduces diffusion distance

  capillary bed is a large network of branched capillaries so increases surface area for diffusion

  small diameter/narrow lumen so reduces blood flow rate so more time for diffusion

  pores in walls between cells allow larger substances through
• explain the formation of tissue fluid

  at the arteriole end of capillaries

  higher blood/hydrostatic pressure inside capillaries (due to contraction of ventricles) than tissue fluid (so net toward force)

  forcing water (and dissolved substances) out of capillaries

  large plasma proteins remain in capillary
• explain the return of tissue fluid to the circulatory system

  at the venule end of capillaries

  hydrostatic pressure reduces as fluid leaves capillary (also due to friction)

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

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

  excess water taken up by lymph capillaries and returned to circulatory system through veins
• suggest and explain causes of excess tissue fluid accumulation

  low concentration of protein in blood plasma or high salt concentration

  water potential in capillary not as low so WP gradient is reduced so more tissue fluid formed at arteriole end/less water absorbed at venule end by osmosis

  high blood pressure so Hugh hydrostatic pressure

  increase outward pressure from arterial end AND reduces inward pressure at venule end so more tissue 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 persons lifestyle or substances in a persons 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