Gas exchange

• The alveoli are adapted to provide a very large surface area by:

  • Their small size and arrangement in clusters, creating large surface area
  • Large blood supply, maintains concentration gradient
  • Thin walls, allows short diffusion path
• Alveoli

  • Is a sphere about 300μm in diamater
  • Total surface area 70 m^2
  • 700 million of them, 350 in each lung
• Describe the dffusion between alveoli and blood capillaries

  • short diffusion path
  • one cell thick
  • alveoli is lined with thin film of moisture
  • gases dissolve into water making diffusion path even smaller
• The trachea branches into two bronchi, each bronchus to eah lung. The bronchi split into smaller branches and then into smaller tubes called bronchioles. Each bronchiole ends with a cluster of microscopic air sacs called alveoli. Capillaries cover 70% of the outside of the alveoli, proving a large surface area.
• Trachea

  ➥Bronchus

  ➥Bronchiole

  ➥Alveoli
• Gas exchange in alveoli

  A) Alveoli

  B) Capillary

  C) Deoxygenated blood in

  D) Oxygenated blood out

  E) Oxygen in

  F) Carbon dioxide out

  
• Lungs

  A) Trachea

  B) Cartilage

  C) Bronchus

  D) Bronchiole

  E) Alveoli

  F) Diaphragm

  G) Ribcage

  H) Internal Intercostal

  I) External Intercostal

  
• How gas exchange occurs:

  1. Upon inhalation, alveoli fill with oxygen
  2. Blood in capillaries surrounding the alveoli is deoxygenated
  3. Oxygen diffuses down the concentration gradient, into the capillary bloodstream
  4. Carbon dioxide diffuses down the concentration gradient from blood in capillary to alveoli