How Humans Breathe

You need to get oxygen from the air into your bloodstream so that it can get to your cells for respiration. You also need to get rid of carbon dioxide in your blood. This happens inside the lungs. Breathing is how the air gets in and out of your lungs. Breathing in involves the intercostal muscles and diaphragm to contract, the Thorax (upper part of the body) volume to increase and a decrease is pressure drawing air in. In contrast breathing out involves the intercostal muscles and diaphragm to relax, the Thorax to decrease in volume and therefore air is forced out. Lungs are like sponges in our Thorax - protected by the ribcage. The air breathed in goes down your Trachea (windpipe) then splits into two tubes called Bronchi, each one going into a lung. Then the Bronchi split into smaller tubes called Bronchioles - which finally lead to small air sacs called Alveoli where the gase exchange of carbon dioxide and oxygen takes place.

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The process of Breathing In

  • Intercostal muscles and diaphragm contract
  • Thorax volume increases
  • Pressure is decreased - drawing air in
  • Diaphragm flattens out
  • Sternum and ribcage are pulled up and out by muscles between ribcage
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The process of Breathing out

  • Intercostal muscles and Diaphragm relax
  • Thorax volume decreases
  • Air is forced out and up the Trachea
  • Ribcage and sternum drop in and down
  • Diaphragm moves up
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How Does Breathing work

  • Air breathed in goes down the Trachea
  • Its split into two separate tubes called Bronchi which lead to each individual lung
  • The Bronchus then splits into even smaller tubes called Bronchioles
  • Finally the Bronchioles lead to tiny tiny air sacs called Alveoli which have a LARGE surface area which therefore means a lot of gas exchange can take place. 
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Gas Exchange in Alveoli

  • The Alveoli are specialised to maximise the diffusion of oxygen and carbon dioxide.

They contain -

  • Enormous surface area
  • A moist lining for dissolving gases
  • Very thin walls
  • Good blood supply


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