gas exchange - humans

• alveoli specialised for gas exchange?

  • one layer of thin cells - short diffusion - increases rate of carbon dioxide and oxygen diffusion across
  • Very large SA - hundred of millions of alveoli
  • moist lining - allow for gases to dissolve - increase rate of diffusion
• how does alveoli carry gas exchange in the body?

  • blood in capillaries just returned to lungs passed aroung body - contains lots of CO2 but little O2
  • Alveoli has fully fresh O2 - diffuse down the gradient and into the blood
  • oxygenated blood repeats cycle again
  • CO2 higher concentration in blood than alveoli so easily diffuses across - once in alveoli we can breathe out
• how does smoking cause a few problems?

  • smoking damages walls of alveoli - reduces the SA for gas exchange and leads to diseases such as emphysema
  • tobacco smoke contains chemicals carcinogen - lead to cancer
  • Tar irritates the bronchi and bronchioles - mucus to be produced - not cleared well and damage cilia - smokers cough and chronic bronchitis