BSC2086 A P II Final Exam Study Guide Lesson 14 Lesson 14 The Respiratory System Part II Introduction to Gas Exchange Respiration two integrated processes o External Respiration Includes all processes involved in exchanging O2 o CO2 with the environment Internal Respiration Involves the uptake of O2 production of CO2 within individual cells Result of cellular respiration Mitochondria use O2 generate CO2 Three 3 Processes of External Respiration o Pulmonary Ventilation breathing o Gas Diffusion across membranes capillaries o Transport of O2 CO2 Between alveolar capillaries Between capillary beds in other tissues Abnormal external respiration is dangerous o Hypoxia Low tissue oxygen levels o Anoxia Complete lack of oxygen that quickly kills cells o Some tissues require a steady flow of O2 more than others Pulmonary Ventilation tract Pulmonary Ventilation Physical movement of air in out of the respiratory o Provides alveolar ventilation air movement into out of alveoli Atmospheric Pressure The weight of air o Compresses our bodies everything around us o Has several important physiological effects Gas Pressure Volume o Boyle s Law Defines the relationship between gas pressure volume P 1 V In a contained gas External pressure forces molecules closer together Movement of gas molecules exerts pressure on container 1 BSC2086 A P II Final Exam Study Guide Lesson 14 Pressure Airflow to the Lungs o Air flows from area of higher pressure to area of lower pressure Concept similar to diffusion o Pulmonary ventilation causes volume changes that create changes in pressure Volume of thoracic cavity changes with expansion or contraction of diaphragm or rib cage o A respiratory cycle consists of An inspiration inhalation An expiration exhalation 2 BSC2086 A P II Final Exam Study Guide Lesson 14 Pressure changes during inhalation exhalation o Can be measured inside or outside the lungs o Normal atmospheric pressure 1 atm 760 mmHg Intrapulmonary Pressure Intra alveolar Pressure o Relative to atmospheric pressure o During relaxed breathing the difference between atmospheric pressure and intrapulmonary pressure is small About 1 mmHg on inhalation or 1 mmHg on exhalation o Maximum Intrapulmonary Pressure Maximum straining a dangerous activity can increase range from 30 mmHg to 100 mmHg If too high can cause alveolar rupture or hernia Intrapleural Pressure Pressure in space between parietal and visceral pleura o Averages 4 mmHg o Maximum 18 mmHg during powerful inhalation o Usually negative o Positive problem will cause lungs to collapse o Remains below atmospheric pressure throughout respiratory cycle o Caused by elastic recoil of lung tissue pulling on chest wall Two areas linked by pleural fluid Pulls on the chest wall as it recoils As you inhale walls expand pull on the lungs Pneumothorax Allows air into pleural cavity o Breaks fluid bond between the pleurae o Can be caused by Ruptured alveoli through visceral pleura Injury that punctures parietal pleura Atelectasis Collapsed lung result of pneumothorax 3 BSC2086 A P II Final Exam Study Guide Lesson 14 Respiratory Muscles o Diaphragm used during normal breathing o External intercostal muscles of the ribs used during normal breathing o Accessory respiratory muscles used during fast breathing Activated when respiration increases significantly Inhalation is ALWAYS active o Muscles used during inhalation Diaphragm Contraction draws air into lungs 75 of normal air movement External Intercostal Muscles Assist inhalation 25 of normal air movement Accessory muscles assist in elevating ribs during fast breathing Sternocleidomastoid Serratus anterior Pectoralis minor Scalene muscles Exhalation can be passive OR active o Passive exhalation relies on relaxation of inhalation muscles recoil of lungs and thoracic cavity elastic rebound o Active exhalation uses muscles during forceful exhalation o Muscles used in active exhalation Internal intercostal muscles transversus thoracis muscles Depress the ribs Abdominal muscles Compress the abdomen Force diaphragm upward Compliance An indicator of expandability o Low compliance greater force needed to fill lungs o High compliance less force needed to fill lungs 4 BSC2086 A P II Final Exam Study Guide Lesson 14 o Factors that affect compliance Connective tissue structure of the lungs Emphysema alveolar tissue damage causes high compliance o Lungs fill to easily but transfer of O2 CO2 less efficient due to damage to respiratory surface Level of surfactant production Low surfactant low compliance Respiratory distress syndrome low compliance Mobility of the thoracic cage Arthritis skeletal disorders reduced compliance Gas Exchange Gas exchange occurs o Between blood alveolar air o Across the respiratory membrane Gas exchange depends on 5 BSC2086 A P II Final Exam Study Guide Lesson 14 o Partial pressures of the gases o Diffusion of molecules between gas liquid Diffusion occurs in response to concentration gradients Dalton s Law Each gas contributes to the total pressure in proportion to its number of molecules o Composition of air Nitrogen N2 79 6 very low solubility in body Oxygen O2 20 9 very soluble in body Water vapor H2O 0 5 Carbon dioxide CO2 0 04 less soluble in body o Atmospheric pressure 760 mmHg produced by air molecules bumping into each other Partial Pressure The pressure contributed by each gas in the atmosphere o All partial pressures together add up to about 760 mmHg o Difference due to contribution of water vapor Henry s Law o When gas under pressure comes in contact with liquid gas dissolves in liquid until equilibrium is reached o At a given temperature amount of gas in a solution is proportional to the partial pressure of that gas o The actual amount of a gas in solution at given partial pressure temperature depends on the solubility of that gas in that particular liquid Normal Partial Pressures o In pulmonary vein plasma after gas exchange at alveoli PCO2 40 mmHg PO2 100 mmHg PN2 573 mmHg Direction rate of diffusion of gases across the respiratory membrane determine different partial pressures and solubilities Five 5 Reasons for Efficiency of Gas Exchange 6 BSC2086 A P II Final Exam Study Guide Lesson 14 o Substantial differences in partial pressure across the respiratory membrane o Distances involved in gas exchange are short Respiratory membrane thin o O2 CO2 are lipid soluble o Total surface area is large Many alveoli o Blood flow airflow are coordinated Partial Pressures in Alveolar Air and Alveolar
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