3.1.1 Gas exchange

• role of elastic fibres in gas exchange?

  in the walls of the trachea, bronchi, bronchioles and alveoli:

  inhalation - lungs inflate and elastic fibres are stretched

  exhalation - fibres recoil to help push air out
• role of smooth muscle in gas exchange?

  in the walls of trachea, bronchi, bronchioles:

  allows their diameter to be controlled - during exercise the smooth muscle relaxes, making the tubes wider --> less resistance to airflow and air can move in and out the lungs more easily
• role of rings of cartilage in gas exchange?

  in the walls of the trachea and bronchi:

  • provides support
  • strong, but flexible - stops trachea and bronchi collapsing when you breathe in and the pressure drops
• describe the process of inspiration?

  1. external intercostal muscles and diaphragm muscles contract
  2. this causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thorax
  3. as the volume of the thorax increases the lung pressure decreases to below atmospheric pressure
  4. this causes air to flow into the lungs
  5. inspiration is an active process - requires energy
• describe the process of expiration?

  1. the external intercostal muscles and diaphragm muscles relax
  2. this causes the ribcage to move downwards and inwards and the diaphragm becomes curved again
  3. the thorax volume decreases, causing the air pressure to increase above atmospheric pressure
  4. air is forced out of the lungs
  5. normal expiration is a passive process - doesn't require energy
  6. during forced expiration, the internal intercostal muscles contract to pull the ribcage down and in
• tidal volume?

  the volume of air in each breath - usually about 0.4dm3
• vital capacity?

  the maximum volume of air that can be breathed in or out
• breathing rate?

  how many breaths are taken - usually in a minute
• oxygen uptake?

  the rate at which an organism uses up oxygen