Adaptations of human gas exchange system

• Alveolar epithelium and capillary endothelium are very thin (1 cell thick)

  • Shortens diffusion distance of gases from alveoli to blood - only has to diffuse through two cells
• Large number of alveoli

  • Increases surface area for gas exchange
• Capillaries that surround the alveoli are very narrow

  • Red blood cells are slowed down to squeeze through one at a time increasing the time for diffusion
• Large number of capillaries around alveoli

  • Circulation constantly removes oxygenated blood to maintain steep concentration gradient
• Constant ventilation of air in and out of lungs

  • Ensures concentration of oxygen in alveoli is higher and concentration of carbon dioxide is lower than blood and therefore maintains steep concentration gradient