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Chapter24A - Chapter24:Physiologyofthe RespiratorySystem...

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Chapter 24: Physiology of the  Respiratory System
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RESPIRATORY PHYSIOLOGY  Definition: complex, coordinated processes that help maintain homeostasis e Ventilation: Movement of air into and out of lungs e External respiration Pulmonary ventilation (breathing) Pulmonary gas exchange e Internal respiration: Gas exchange between the blood and tissues Cellular respiration e Regulation of respiration
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Respiratory System Functions  Gas exchange : Oxygen enters blood and carbon dioxide leaves e Regulation of blood pH : Altered by changing blood carbon dioxide levels e Voice production : Movement of air past vocal folds makes sound and speech e Olfaction : Smell occurs when airborne molecules are drawn into nasal cavity 4
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Blood and Lymphatic Supply Sources of blood to lungs: Pulmonary circulation e Two lymphatic supplies: superficial Drains superficial lung tissue and visceral pleura deep lymphatic vessels. Exit from hilus Deep drain bronchi and associated C.T. No lymphatics drain alveoli 5
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Ventilation Movement of air into and out of lungs e Air moves from area of higher pressure to area of lower pressure e Boyle’s Law : P = k/V, where P = gas pressure, V = volume, k = constant at a given temperature e If barometric pressure is greater than alveolar pressure, then air flows into the alveoli. e If diaphragm contracts, then size of alveoli increases. Remember P is inversely proportionate to V; so as V gets larger (when diaphragm contracts), then P in alveoli gets smaller. Compliance: ability of pulmonary tissues to stretch, thus making inspiration possible 6
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Compliance Measure of the ease with which lungs and thorax expand Conditions that decrease compliance Pulmonary fibrosis: - deposition of inelastic fibers in lung (emphysema) Pulmonary edema Respiratory distress syndrome Increased resistance to airflow caused by airway obstruction (asthma, bronchitis, lung cancer) Deformities of the thoracic wall (kyphosis, scoliosis) 7
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Changing Alveolar Volume: Lung Recoil Causes alveoli to collapse resulting from Elastic recoil : elastic fibers in the alveolar walls Surface tension : film of fluid lines the alveoli. Where water interfaces with air, polar water molecules have great attraction for each other with a net pull in toward other water molecules. Tends to make alveoli collapse. Surfactant : Reduces tendency of lungs to collapse by reducing surface tension. Produced by type II pneumocytes. Respiratory distress syndrome ( hyaline membrane disease ). Common in infants with gestation age of less than 7 months. Not enough surfactant produced. 9
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Pleural Pressure Negative pressure Alveoli expand when pleural pressure is low enough to overcome lung recoil e Pneumothorax is an opening between pleural cavity and air that causes a loss of pleural pressure 10
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Expiration A passive process that begins when the inspiratory muscles are relaxed, which decreases the size of the thorax
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