human gas exchange system

• Organ: Lungs

  Gas exchange surface: Alveoli

  1. large surface area - many alveoli with folded walls
  2. Thin for a short diffusion pathway - alveoli walls are 1 cell thick and squamous epithelium
  3. permeable - cells allow diffusion of O2 and CO2 but not nitrogen gas
  4. Moist - O2 and CO2 can dissolve and diffuse
  5. Maintain a concentration gradient:

  • Large network of capillaries which remove oxygenated blood and deliver deoxygenated blood to the alveoli
  • Ventilation of the lungs draws in the air with a higher O2 concentration
• Human system:

  Mouth - trachea - bronchi - bronchioles - alveoli - blood - body cells
• Mammals inhalation

  Volume of thorax increases:

  • contract diaphragm which flattens
  • Contract the intercostal muscles and the ribcage moves up and out

  Volume of alveoli increases = pressure in alveoli decreases:

  • Outer pleural membrane on the ribcage moves up and out - decreasing pressure
  • Inner pleural membrane on the lung surface moves up and out - increasing volume = decreasing pressure in alveoli
  • pressure drops below atmospheric
  • air enters down a pressure gradient
  • alveoli inflate into thoracic space available
• Mammal expiration

  • the intercostal muscles relax allowing the ribcage to move downwards and inwards
  • The diaphragm relaxes and becomes dome shaped
  • The volume of the thoracic cavity decreases = pressure inside the thoracic cavity increases above atmospheric
  • moving air out of the lungs down a pressure gradient
• bronchioles become restricted and inflamed during an asthma attack
• The layer of cartilage in the trachea is to prevent the trachea from closing during inspiration. It doesn't form a complete ring to allow room for the oesophagus to expand when swallowing food.