2.3a

• Haemocoel


  The main body cavity found in most invertebrates that contains a circulatory fluid
• Transport systems in animals


  • Have a suitable medium to carry dissolved substances
  • Have a pump to move the materials
  • Some have a respiratory pigment, e.g. haemoglobin, to carry dissolved gases
  • Use a system of vessels with valves to ensure a one-way flow to all parts of the body
• Open circulatory systems


  • Blood does not move around the body in blood vessels
  • Cells are bathed by blood or a fluid called haemolymph in a fluid filled space around the organs called a haemocoel
  • Blood returns slowly to the dorsal, tube shaped-heart
  • No need for a respiratory pigment as oxygen is supplied directly to tissues via the tracheal system
  • Relatively inefficient, not responsible for the distribution of respiratory gases in insects
• Closed circulatory systems


  • Blood is transported more quickly under a higher pressure, to all parts of the animal's body
  • Single circulatory system involves blood passing through the heart once
  • Double circulatory system involves blood passing through the heart twice, with one circuit supplying the lungs and one supplying the body
• Advantages of double circulatory system

  • Higher blood pressure and faster circulation can be sustained in systemic circulation
  • Oxygenated and deoxygenated blood are kept separate, which improves oxygen distribution
• Blood flow through the heart

  1. Blood enters the right atrium from the vena cava

  2. Right atrium contracts, forcing blood through the right AV valve into the right ventricle

  3. Right ventricle contracts, forcing blood out through the right semi-lunar valve to the lungs

  4. Oxygenated blood returns from the lungs to the left atrium

  5. Left atrium contracts, forcing blood through the left AV valve into the left ventricle

  6. Left ventricle contracts, forcing blood out through the left semi-lunar valve to the body
• Systole


  Contraction of the heart
• Diastole


  Relaxation of the heart
• Valves ensure that blood flows in a unidirectional manner, i.e. they prevent backflow of blood
• Sinoatrial node (SAN)


  Initiates the wave of excitation across both atria
• Atrioventricular node (AVN)


  Allows the wave of excitation to spread from the atria to the ventricles
• Bundle of His


  Modified cardiac muscle fibre passing from the AVN to the base of the ventricle through the septum of the heart
• Purkinje fibres


  Network of fibres in the wall of the ventricles that carry the wave of excitation upwards, causing the ventricles to contract from base to apex
• Myogenic


  The heartbeat is initiated within the cardiac muscle
• Sinoatrial node (SAN)


  Initiates a wave of excitation across both atria
• Cardiac cycle


  1. Atrial systole

  2. Ventricular systole
• Atrial systole


  • Wave of excitation spreads out from the sinoatrial node (SAN) across both atria
  • Both atria start contracting
  • Wave cannot spread to ventricles due to layer of connective tissue
  • Wave spreads via the atrioventricular node (AVN), through the Bundle of His to apex of ventricle
• Ventricular systole


  • The Bundle of His branches into Purkinje fibres carrying wave upwards through ventricle muscle causing it to contract
  • Ventricle contraction is therefore delayed and contraction is from base upwards
• These events can be seen in an ECG (electrocardiogram)
• Purkinje fibres


  Network of fibres in the wall of the ventricles
• Components of blood


  • Plasma (55%)
  • Cells (45%)
• Red blood cells (erythrocytes)


  • Contain haemoglobin
  • Biconcave shape increases surface area for absorption and release of oxygen
  • No nucleus so can carry more haemoglobin but have limited life
• Types of white blood cells


  • Granulocytes (phagocytic)
  • Lymphocytes (develop into cells that produce antibodies)
• Plasma


  • 90% water, contains dissolved solutes (e.g. glucose, amino acids, hormones, plasma proteins)
  • Responsible for distribution of heat and transport of carbon dioxide as HCO3- ions
  • Transports excretory products such as urea
• Transport of oxygen


  1. Haemoglobin binds to oxygen in the lungs

  2. Haemoglobin releases oxygen to respiring tissues
• Oxygen-haemoglobin dissociation curve


  • Shows how haemoglobin's affinity for oxygen changes with partial pressure
  • At high partial pressures, affinity is high so oxyhaemoglobin does not easily release oxygen
  • At low partial pressures, oxygen is released rapidly to respiring tissues where it is needed
• Haemoglobin


  • Each molecule can accommodate four molecules of oxygen
  • Cooperative binding - as oxygen molecules bind, haemoglobin changes slightly making it easier for the next one to bind
  • Fourth oxygen molecule is more difficult to bind, requiring a large increase in partial pressure of oxygen
• Animals adapted to low oxygen environments


  • Llama
  • Lugworm
• Haemoglobin in low oxygen environments


  • Has higher affinity for oxygen than normal haemoglobin
  • Dissociation curve is shifted to the left, meaning haemoglobin is more saturated at the same partial pressure of oxygen
• Foetal haemoglobin


  Has higher affinity for oxygen than maternal blood, allowing it to absorb oxygen from the mother's blood via the placenta
• Carbon dioxide concentrations in the blood rise during exercise


  Haemoglobin dissociation curve shifts to the right
• Bohr effect


  Haemoglobin's affinity for oxygen is reduced, so more oxygen is released at the same partial pressure of oxygen, supplying oxygen more quickly to respiring tissues
• Ways carbon dioxide is carried in the blood


  • Dissolved in plasma (5%)
  • As HCO3- ions in the plasma (85%)
  • Bound to haemoglobin as carbamino-haemoglobin (10%)
• Reactions in a red blood cell


  1. Carbon dioxide diffuses into the red blood cell

  2. Carbonic anhydrase catalyses the reaction between carbon dioxide and water forming carbonic acid

  3. Carbonic acid dissociates into HCO3- and H+ ions

  4. HCO3- diffuses out of the red blood cell

  5. Cl- ions diffuse into the cell to maintain electrochemical neutrality (chloride shift)

  6. H+ ions combine with oxyhaemoglobin forming haemoglobinic acid (HHb) and releasing oxygen

  7. Oxygen diffuses out of the cell
• Formation of tissue fluid


  1. Hydrostatic pressure created by blood pressure at the arteriole end forces materials out of the capillaries

  2. Most of the water is reabsorbed by osmosis at the venule end of the capillary bed

  3. Excess tissue fluid drains into the lymphatic system and returns to the venous system via the thoracic duct