The Respiratory Cycle

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Respiratory Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. No airflow Atmospheric pressure 760 mm Hg Pleural cavity Diaphragm Intrapulmonary pressure 760 mm Hg Intrapleural pressure 756 mm Hg Ribs swing upward like bucket handles during inspiration. 1 At rest, atmospheric and intrapulmonary pressures are equal, and there is no airflow. Ribs swing downward like bucket handles during expiration. 2 Inspiration 4 Pause Airflow Airflow Intrapleural pressure –6 mm Hg Intrapulmonary pressure –3 mm Hg Intrapleural pressure –4 mm Hg Intrapulmonary pressure +3 mm Hg Diaphragm flattens 3 Expiration Diaphragm rises Rib Sternum Ribs elevated, thoracic cavity expands laterally Sternum Rib Sternum swings up, thoracic cavity expands anteriorly Rib Sternum Ribs depressed, thoracic cavity narrows Sternum Rib Sternum swings down, thoracic cavity contracts posteriorly 2 In inspiration, the thoracic cavity expands laterally,vertically 3 In expiration, the thoracic cavity contracts in all three directions; and anteriorly; intrapulmonary pressure drops 3 mm Hg below intrapulmonary pressure rises 3 mm Hg above atmospheric atmospheric pressure, and air flows into the lungs. pressure, and air flows out of the lungs.
Airflow (1 of 2) • pressure is one determinant of airflow • resistance is the other – the greater the resistance the slower the flow • three factors influencing airway resistance – (1) diameter of the bronchioles • bronchodilation – increase in the diameter of a bronchus or bronchiole – epinephrine and sympathetic stimulation stimulate bronchodilation – increase air flow • bronchoconstriction – decrease in the diameter of a bronchus or bronchiole – histamine, parasympathetic nerves, cold air, and chemical irritants stimulate bronchoconstriction – suffocation from extreme bronchoconstriction brought about by anaphylactic shock and asthma
Page 1 and 2: Chapter 22 The Respiratory Cycle
Page 3 and 4: Physics, Inspiration & Respiration
Page 5 and 6: Inspiration & Boyle’s Law • int
Page 7: Expiration • relaxed breathing -
Page 11: More About Alveolar Surface Tension

The Respiratory Cycle

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