ALVEOLI

• In humans where does gaseous exchange happen?

  in the alveoli
• what is each alveolus made from?

  A single layer of thin, flat cells called alveolar epithelium
• There is a huge number of alveoli in the lungs which means.......?

  There is a big surface area for exchanging oxygen and carbon dioxide
• what are the alveoli surrounded by?

  a network of capillaries
• what diffuses out of the alveoili?

  oxygen
• where does oxygen diffuse?

  Out of the alveoli

  across the alveolar epithelium and the capillary endpothelium

  and into haemoglobin in thr blood
• what is the capillary endothelium?

  a type of epithelium that forms the capillary wall
• what diffuses into the alveoili?

  carbon dioxide
• where does carbon dioxide diffuse?

  into the alveoili from the blood, and is breathed out
• where does oxygen from the air move?

  • down the trachea, bronchi and bronchioles into the alveoli
  • this happens DOWN a PRESSURE GRADIENT
  • once in the alveoli the oxygen diffuses across the alveolar epithelium then the capillary endothelium , ending up in the capillary itself
  • this happens DOWN a DIFFUSION GRADIENT
• how are the alveoli adapted for gas exchange/?

  • thin exchange surface- alveolar epithelium is only one cell thick so short diffusion pathway which speeds up diffusion
  • Large number of alveoli = large surface area for gas exchange
  • there is also a steep concentration gradient of oxygen and carbon dioxide between the alveoli and the capillaries which increases the rate of diffusion. this is constantly maintained by the flow of BLOOD and ventilatioj