3.3.4.1 Animals

• Haemoglobin

  A protein with a quaternary structure - having four polypeptide chains bonded together. Each haem group has an iron ion in the centre. One oxygen molecule can bind to one haem so four oxygen molecules and be carried by one Hb. When oxygen is bound to Hb it is called oxyhaemoglobin.
• Cooperative nature of oxygen binding

  The first oxygen molecule binds to haemoglobin and causes a change of shape, this makes it easier for the other oxygen molecules to bind.
• Affinity for oxygen

  How readily haemoglobin loads with oxygen. Affinity changes as oxygen concentration varies
• Loading of oxygen at the gas exchange surface:

  • Partial pressure is high
  • Oxygen diffuses down the concentration gradient from alveoli to red blood cells
  • Hb has a high affinity for oxygen
  • So loads readily with oxygen
• Unloading of oxygen at the tissues:

  • Partial pressure is lower
  • Hb has a lower affinity for oxygen
  • Unloads more readily
  • Diffuses down concentration gradient from red blood cells to tissues
• Large SA:V or active animals have a high rate of respiration so will need Hb with a lower affinity for oxygen so it will unload more readily.

  
• Left shift in affinity for oxygen ensures that only a small drop in partial pressure gives a large drop in percentage saturation to dissociate oxygen to respiring cells
• Mass transport

  The movement of many dissolved molecules/ions in bulk over large distances, all travelling at the same rate in a transport medium
• What does mass transport need?

  A network of closed vesicles to keep blood inside

  Pressure differences to keep blood moving

  One way flow to keep blood moving in one direction

  Way to alter flow to different regions
• Double circulatory system

  Blood passes through the heart twice in a full circuit of the body
• The heart

  Made of cardiac muscle

  Needs its own supply of oxygen and glucose delivered to cardiac muscle cells by coronary arteries for aerobic respiration to produce ATP for cardiac muscle contraction

  
• The cardiac cycle:

  • Diastole - Cardiac muscle relaxes, semi lunar valve closes, atria fill with blood forcing the atrioventricular valve open. Ventricles fill with blood
  • Atrial systole - Cardiac muscle of atria contracts, increasing the pressure in the atria. Blood is forced into the ventricles. Atrioventricular valve open and semi lunar valve closed
  • Ventricular systole - Cardiac muscle of ventricles contract, increasing pressure in the ventricles. Blood is forced into the arteries. Semilunar valve is force open and the atrioventricular valve is forced shut to prevent backflow
• Cardiac output

  Volume of blood pumped out of the left ventricle in one minute
• Stroke volume

  volume of blood pumped by the loft ventricle in each heart beat
• Heart rate


  the number of times the heart beats per minute
• Cardiac output = stroke volume x heart rate
• Arteries 


  Carry oxygenated blood under high pressure and with pulsed flow away from the heart, branches into smaller arterioles
• Arterioles 


  Branched from arteries to capillaries - still high pressure and pulsed flow but lower
• Veins 


  Carry oxygenated blood under low pressure back to the heart
• Capillaries 


  Site of metabolic exchange between blood and cells
• Adaptions for function - Arteries

  • Thicker walls with more muscle and elastic tissue to withstand pressure
  • Folded endothelium to provide large surface area for large blood surges
  • Smaller lumen helps keep high pressure
  • More elastic tissue which stretches when there is a high pressure and recoils when it is low to even out pressure flow
  • Branching to increase total surface area - increases friction between blood and vessel walls
  • Muscle tissue vasoconstricts to narrow and vasodilates to relax
• Adaptions for function - veins

  • Thinner walls with less muscle and elastic tissue as there is no need to withstand pressure
  • Larger lumen so the blood is returned to the heart at the same rate as it left the arteries
  • Low pressure blood and not pulsed
  • Needs skeletal muscle to contract and valves to prevent backflow
  • As diastole occurs blood is sucked into the atria
• Adaptions for function - capillaries

  • Site of metabolic exchange between blood and cells
  • Wall one cell thick to provide a short diffusion pathway
  • Endothelial cells thin/flat
  • Gaps between cells to allow water and molecules in and out faster
  • Small lumen diameter - red blood cells only just fit through - slows blood flow so there is more time for efficient diffusion
  • Many capillaries to provide a large surface area
• Formation of tissue fluid:

  1. High hydrostatic pressure at the ateriole end
  2. Water and small water-soluble molecules are forced through the capillary walls forming tissue fluid
  3. Proteins and blood cells in the plasma are too large to be forced out and remain in the blood
  4. The water potential is lower at the venule end of the capillary bed due to plasma proteins and less water
  5. Water moves via osmosis back into blood
  6. Lymph vessel collects only excess tissue fluid which returns to blood
• Oedema


  build up of tissue fluid