Mechanism of breathing and exchange of gases in the lungs

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Last updated 9:25 AM on 9/17/26
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4 Terms

1
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What are the two sets of intercostal muscles?

  • internal intercostal muscles - contraction leads to expiration

  • external intercostal muscles - contraction leads to insipration


<ul><li><p>internal intercostal muscles - contraction leads to expiration</p></li><li><p>external intercostal muscles - contraction leads to insipration</p></li></ul><p></p>
2
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Inspiration process

  • external intercostal muscles contract/internal intercostal muscles relax

  • ribs pulled upwards and outwards, increasing volume of the thorax

  • diaphragm muscles contract - flattens - increases vol. of thorax

  • increased vol. of thorax = reduction of pressure in lungs

  • atmospheric pressure is now greater than pulmonary pressure and so air is forced into the lungs


<ul><li><p>external intercostal muscles contract/internal intercostal muscles relax</p></li><li><p>ribs pulled upwards and outwards, increasing volume of the thorax</p></li><li><p>diaphragm muscles contract - flattens - increases vol. of thorax</p></li><li><p>increased vol. of thorax = reduction of pressure in lungs</p></li><li><p>atmospheric pressure is now greater than pulmonary pressure and so air is forced into the lungs</p></li></ul><p></p>
3
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Expiration process

  • IIM contract/EIM relax

  • ribs move downwards and inwards - decreasing vol. of thorax

  • diaphragm muscles relax and so it is pushed up against the contents of the abdomen

  • vol. of thorax decreases

  • decreased vol. of thorax increases pressure in lungs

  • air is forced out of lungs by increased pulmonary pressure


<ul><li><p>IIM contract/EIM relax</p></li><li><p>ribs move downwards and inwards - decreasing vol. of thorax</p></li><li><p>diaphragm muscles relax and so it is pushed up against the contents of the abdomen </p></li><li><p>vol. of thorax decreases</p></li><li><p>decreased vol. of thorax increases pressure in lungs</p></li><li><p>air is forced out of lungs by increased pulmonary pressure</p></li></ul><p></p>
4
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Why is the diffusion of gases between blood and alveoli rapid?

  • red blood cells slow as they pass through pulmonary capillaries allowing more time for diffusion

  • distance between alveolar air and rbc is reduced as rbcs are flattened against capillary walls

  • walls of alveoli and capillaries are very thin and so diffusion distance is short

  • alveoli and pulmonary capillaries have very large total surface area

  • steep conc.grad. due to ventilation and blood circulation

  • blood flow through pulmonary capillaries maintains conc.grad


<ul><li><p>red blood cells slow as they pass through pulmonary capillaries allowing more time for diffusion</p></li><li><p>distance between alveolar air and rbc is reduced as rbcs are flattened against capillary walls</p></li><li><p>walls of alveoli and capillaries are very thin and so diffusion distance is short</p></li><li><p>alveoli and pulmonary capillaries have very large total surface area</p></li><li><p>steep conc.grad. due to ventilation and blood circulation</p></li><li><p>blood flow through pulmonary capillaries maintains conc.grad</p></li></ul><p></p>