Gas exchange in the alveolus

• what are alveoli?

  the gas exchange surfaces
• why are alveoli efficient at gas exchange?

  • large surface area relative to the volume of the body
  • gases dissolve in the surfactant moisture lining alveoli
  • have walls made of squamous epithelium - only 1 cell thick so diffusion pathways for gases is short
  • surrounded by an extensive capillary network which maintains diffusion gradients, as O2 is rapidly brought to the alveoli and CO2 is rapidly carried away
  • capillary walls are also only 1 cell thick which contributes to the short diffusion pathway for gases
• why are diffusion pathways short in alveoli?

  as the walls of both the alveoli and the capillaries that surround it are only 1 cell thick
• how does gas exchange in alveoli work?

  • deoxygenated blood enters the capillaries surrounding the alveoli
  • oxygen diffuses out of the air in the alveoli into the red blood cells in the capillary
  • carbon dioxide diffuses out of the plasma in the capillary into the air in the alveoli, from where its exhaled
• what is this a diagram of?

  the process of gas exchange in alveoli

  
• what is the % of oxygen in inspired air and why?

  • 20%
  • oxygen is absorbed into the blood at the alveoli and used in aerobic respiration
• what is the % of oxygen in expired air and why?

  • 16%
  • oxygen is absorbed into the blood at the alveoli and used in aerobic respiration
• what is the % of carbon dioxide in inspired air and why?

  • 0.04%
  • carbon dioxide produced by aerobic respiration diffuses from the plasma into the alveoli
• what is the % of carbon dioxide in expired air and why?

  • 4%
  • carbon dioxide produced by aerobic respiration diffuses from the plasma into the alveoli
• what is the % of nitrogen in inspired air and why?

  • 79%
  • nitrogen is neither absorbed nor used so all that is inhaled gets exhaled
• what is the % of nitrogen in expired air and why?

  • 79%
  • nitrogen is neither absorbed nor used so all that is inhales gets exhaled
• what is the % of water vapour in inspired air and why?

  • variable
  • the water content of the atmosphere varies - alveoli are permanently lined with moisture; water evaporates from them and is exhaled
• what is the % of water vapour in expired air and why?

  • saturated
  • the water content of the atmosphere varies - alveoli are permanently lined with moisture; water evaporates from them and is exhaled
• what is the equation to work out absorption efficiency?

  $\frac{\%\ of\ oxygen\ inhaled}{\%\ of\ air\ that\ is\ oxygen\ }$