The Respiratory and Circulatory Systems


Introduction to the Lungs

  • Send oxygenated blood back to the heart through the pulmonary vein.
  • Trachea --> Bronchus --> Bronchioles ---> Alveoli
  • The alveoli are lined with squamous epithelial cells, extremely flat cells with a large surface area to enable the best gaseous exchange.


1 of 4



  • Intercostal muscles contract --> ribcage goes up and out
  • Diaphragm muscles contract and go flat, allowing the lungs to expand with air
  • In the thorax, the volume increases and the pressure decreases, so air comes rushing in


  • Intercostal muscles relax, causing the ribcage to "get smaller"
  • Diaphragm muscles contract making it become dome shaped, forcing the lungs to get smaller
  • The volume in the thorax decreases and the pressure is increased to that above the external pressure, as a result the used air is expelled.
2 of 4


  • A large globular proteins- 4 polypeptide chains= quatinery structure
  • Inside red blood cells
  • Haem groups contain iron (Fe)

Behaviour of haemoglobin and oxygen:

  • Able to load up more O2 than expected at lungs, and unload more O2 than expected at muscles
  • Haemoglobin unloads O2 more easily under higher pressures and more acidic pHs, active muscles are warmer and have more acidic pHs due to CO2 and lactic acid, making haemoglobin effective

The Bohr Shift/Effect:

  • Explores effect on haemoglobin of CO2 and temperature, basically the more they are found, the easier the dissociation of oxygen from Hb --> this is just what respiring muscles need!
3 of 4

Transport Of Carbon Dioxide

  • 5% dissolved directly into plasma
  • 10% combines with haemoglobin to form carbaminohaemoglobin
  • 85% are transported as hydrogencarbonate ions

Where do the hydrogencarbonate ions come from?:

1. Carbon dioxide reacts with water to form carbonic acid (H2CO3), the reaction is catalysed by carbonic anhydrase.

2. The carbonic acid dissociates to form hydorgencarbonate ions (HCO3) and hydrogen ions (H+)

To stop becoming too acidic, haemoglobin takes in the H+ ions to form haemoglobonic acid.

4 of 4


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Human, animal and plant physiology resources »