Ventilation (gas exchange)

• The human gas exchange

  
• Inhalation and exhalation

  
• During inspiration (inhaling)...


  . The external intercostal muscles contract (pulls the ribs up and out)

  . The internal intercostal muscles relax.

  . The diaphragm contracts (downwards from dome position)

  . The air pressure in the lungs initially drops.

  . The lung volume increases (to decrease the pressure)
• How does air move in during inspiration?

  Air moves into the lungs, from the atmospheric pressure into lower pressure.
• During expiration (exhaling)...


  . The external intercostal muscles relax.

  . The internal intercostal muscles contract (pulling ribs down and in)

  . The diaphragm relaxes (returns to a domed shape)

  . The pressure is greater than the atmosphere. It drops as air moves out.

  . The lung volume decreases (to increase pressure)
• How does air move out during expiration?

  Air moves out of the lungs, from high pressure in the lungs out to atmospheric pressure.
• Alveoli


  . The air sacs at the end of the bronchioles

  . Surrounded by capillaries

  . There is a very short diffusion distance as alveoli are made up of a single layer of cells and capillaries.

  CO2 will diffuse out as there is a high concentration of carbon dioxide

  O2 will diffuse from the alveoli, across the epithelium and into blood.
• Alveoli adaptations


  There are 300 million in each human lung, creating a very large surface area for gas exchange.

  The alveoli epithelium cells are very thin, to minimise diffusion distance

  Each alveolus is surrounded by a network of capillaries to remove exchanged gases, and therefore maintains a concentration gradient.
• What does the pleural fluid do in the pleural membranes?

  Acts as a lubricant as the lung volume changes (helps reduce friction)
• What is the scientific name when an internal intercostal muscle contracts and an external intercostal muscle relaxes?

  Antagonist pairing (they are doing different actions)