11End_of_YrRespiratory

11End_of_YrRespiratory - 1 End of Year Review - RESPIRATORY...

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1 End of Year Review - RESPIRATORY PHYSIOLOGY April Apperson, M.S., UCSD SOM OESS I. Function of lungs is gas exchange and gas exchange requires both airflow and blood flow. A. Gas exchange between the air in alveolar sacs and pulmonary capillaries surrounding each alveolus adds O 2 to, and removes CO 2 from pulmonary capillary blood. 1. Tissue metabolism requires O 2 for oxidative- phosphorylation, and produces CO 2 via the TCA cycle. 2. Ventilation (L/min airflow) moves inspired air (high P IO2 , no P ICO2 ) through the airways to the alveoli and removes expired alveolar gas (lower P AO2 , higher P ACO2 ). 3. Pulmonary arterial blood flow delivers high CO 2 , low O 2 blood from to pulmonary capillaries , and pulmonary venous blood flow delivers high O 2 , low CO 2 blood to the left heart. B. Airways and blood-gas barrier 1. Airways form a series of bifurcating tubes beginning with the trachea and terminating in alveoli. a. Conducting airways = airway generations 0 - 16 – trachea through the terminal bronchioles ; these contain no alveoli and cannot exchange gas, so their volume = anatomic dead space = V D 5% of resting lung volume. b. Respiratory zone airways = airway generations 17 – 23 – respiratory bronchioles through the alveolar sacs; these contain alveoli and conduct all gas exchange. •Respiratory zone volume alveolar volume = V A 95% of resting lung volume •The complex of airways and alveoli branching from each terminal bronchiole is an acinus, so all acinar volume = alveolar volume = site of gas exchange. 2. Blood-gas barrier = type I alveolar cell, basal lamina, endothelial cell (not across the nucleus). a. Air-water interface between alveolar gas and thin layer of interstitial fluid covering alveolar epithelial cells creates surface tension , which contributes to elastic recoil of lung. •Elastic recoil is proportional to lung volume - lung is trying to recoil to minimum volume (MV). •Elastic recoil is inversely proportional to lung compliance – stiffer lungs have more recoil. b. Surfactant dipalmitoyl phosphatidylcholine (DPPC) secreted by Type II alveolar cells forms amphipathic interface between air and water and decreases air-water surface tension , which: •Increases lung compliance, which decreases the work of the lung (less stiff lung to inflate). •Prevents atalectasis by preventing smaller radius alveoli from overfilling larger alveoli. •Helps prevent pulmonary edema by preventing surface tension from decreasing interstitial pressure (P ISF ) and thus increasing filtration enough to cause edema. c. A saline-filled lung has greater compliance (no air-water surface) but virtually no hysteresis on the pressure-volume curve because surfactant has been washed away. •Surfactant effect on surface tension is non-linear and causes the inspiration pressure-volume curve to differ from the expiration pressure-volume curve – this is called hysteresis.
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11End_of_YrRespiratory - 1 End of Year Review - RESPIRATORY...

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