Mechanics of breathing

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Biological Sciences
BIO 105
Bradley Wetherbee

Mechanics of breathing Thoracic structures • Must be strong enough to protect vital organs • Flexible enough to expand with lungs • Provided by rib cage Inspiration • Diaphragm contracts and thoracic volume increases • Intercostal muscles between ribs also contract- lateral expansion of thoracic cavity- lung volume increases • Air pressure in lungs decreases and air flows into lungs Expiration • Passive process • Thorax and lungs recoil, respiratory muscles relax • Volume decreases and pressure increases • Pressure in alveoli increases and air pushed out of lungs Gas exchange in the lungs • Partial pressure of a gas o Air is a mix of gases- each present at some concentration o Each gas has its own partial pressure  P atm= PN₂ + PO₂ + PCO₂ (N, O, CO₂)  Atmospheric pressure= 760mm Hg  Air is 21% O₂ so (760x .21)= 16mm Hg P O₂  Partial pressure of O₂ in air is 160mm Hg o Gas within air will move according to its partial pressure:  Air in alveoli has a certain oxygen concentration  Blood has a certain oxygen concentration • Partial pressure of gases in blood o Higher concentration of O₂ in alveoli= diffusion of oxygen into blood o Occurs very rapidly- many alv
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