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Lec 1

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Mc Kay+ French

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38 Pulmonary Gas ExchangeJanuary 07 2008 Structure of respiratory tract mechanics of respiration Primary Function of the LungsFunction determines structure and structure determines function Remember The primary function of the lungs is to exchange gases between blood and airOxygenCarbon Dioxide 21 in Air16 in Blood0 in Air5 in Blood Gas exchange occurs by passive diffusion across the alveolar membrane separating air and blood Passive DiffusionPassive diffusion is proportional to 1 The partial pressure difference of the gases between air and blood o Recall Partial PressureFractional Concentration x Total PressureNOTE Fractional concentration applies to gases onlyConcentration applies to gases in liquids like blood more later F x PIn universal symbols PCO2CO2Bo Daltons law of partial pressures The sum of the partial pressurestotal pressure PPPIn air PO2CO2N2Bo For exampleis 760 mmHg or 100 kPa and F is 21 soPBO21596 mmHg or 21 kPaPO2of the alveolar membrane 2 The surface areao Maximum surface area in minimum volumemaximum diffusion of the alveolar membrane 3 The thicknessHow to maximize surface area in minimum volume2 in 5 LIn normal lungs 85 m Many small blood vessels capillaries wrap around 300 million small air sacs alveoli each 300 m in diameterThe alveoli are so closely packed that they lose their spherical shape and become polygonal How do you get the air to the alveoli The Airways To get the air to the alveoli a treelike system of branching tubes is used The airway starts at the tracheast bifurcationRight and Left Main Bronchi1ndth to 4 bifurcationLobar Bronchi2 o NOTE The above have cartilage to maintain their shapethth to 11 bifurcationSegmental Bronchi5thth to 16 bifurcationTerminal Bronchioles12o NOTE This is stabilized by bronchiolar muscles this is where asthma strikesWhen the bronchiolar muscles contract airways narrowmakes it harder to breathe NOTE All of the above are conducting airways No gas exchange occurs and so they make an anatomical dead space more later on that 1
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