KIN 292 1nd Edition Lecture 28 Outline of Last Lecture Chapter 15 continued Outline of Current Lecture I II III IV V 16 1 Overview of Respiratory Function 16 2 Anatomy of the Respiratory System 16 3 Forces for Pulmonary Ventilation 16 4 Factors Affecting Pulmonary Ventilation 16 5 Clinical Significance of Respiratory Volumes and Air Flows Current Lecture External respiration o Pulmonary ventilation o Exchange between lungs and blood in pulmonary circulation o Transportation in blood o Exchange between blood and body tissues in systemic circulation Internal respiration o Oxidative phosphorylation Apnea cessation of breathing When it occurs during sleep sleep apnea o May happen many times per hour and person may be unaware until being informed by someone who hears all of the sleep noises including snoring o Decreases sleep quality and quality of life o Treatments range from to behavioral modifications such as sleeping on side losing weight no depressant drugs or booze o 2 main types Obstructive sleep apnea most common due to excessive relaxation of muscles in upper airways Central sleep apnea caused by problem within respiratory centers in brain The Respiratory Tract These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Functions of the conducting zone o Air passageway 150 mL in volume dead space no gas exchange o Increases air temperature to body temperature o Humidifies air Epithelium of the conducting zone o Goblet cells Secrete mucus to trap foreign particles o Ciliated cells Cilia move mucus particles toward mouth Mucus escalator o Mucus accumulation increases infections and growth of bacteria o Smoking paralyzes cilia disabling elevator so airways are cleared by coughing partially responsible for the smoker s cough Alveoli Site of gas exchange 300 million alveoli in the lungs size of tennis court Rich blood supply capillaries form sheet over alveoli Type I alveolar cells make up wall of alveoli Single layer of epithelial cells Type II alveolar cells secrete surfactant Alveolar macrophages engulf foreign bodies and take what s left of them up the mucus elevator Chest wall airtight protects lungs rib cage sternum thoracic vertebrae connective tissue intercostal muscles Pleural sac around each lung Intrapleural space is filled with intrapleural fluid Volume 15 mL 16 3 Forces of Pulmonary Ventilation Pulmonary pressures Atmospheric pressure Patm o 760 mmHg at sea level Other pressures often expressed relative to Patm so it is set at 0 Intra alveolar pressure Palv o Pressure of air in alveoli Intrapleural pressure Pip o Pressure inside pleural sac Transpulmonary pressure Palv Pip o Distending pressure across the lung wall Intrapleural pressure Pressure inside pleural sac o Always negative under normal conditions and less than Palv o Varies with respiration phase Rest 4 mm Hg o Negative due to elasticity in lungs and chest wall o Lungs recoil inward as chest wall recoils outward o Opposing forces pull on intrapleural space o Surface tension of intrapleural fluid prevents wall and lungs from pulling apart Transpulmonary pressure and alveoli o Transpulmonary pressure difference between Palv and Pip o It is the distending pressure across the lung wall o Transpulmonary pressure increases during inspiration causing lungs to expand increasing volume of alveoli Pneumothorax Pressure in pleural sac always negative because opposing forces exerted by chest wall and lungs pull parietal and visceral pleura apart Surface tension of intrapleural fluid keeps the two pleura from pulling apart Pip is always less than Palv which keeps the alveoli open A pneumothorax air in the ip space causes Pip to equilibrate with PAtm and eliminates the pressure difference between Palv needed to keep lungs inflated Mechanics of Breathing Forces for air flow o Force for flow pressure gradient same as with blood flow o Atmospheric pressure remains constant during breathing cycle o Thus alveolar pressure changes affect gradients o Boyle s law pressure is inversely related to volume o Can change alveolar pressure by changing its volume o Resistance to air flow R is related to airway radius and mucus Alveolar pressure Palv is given relative to atmospheric pressure set Patm 0 mm Hg Patm is760 mm Hg at sea level o Decreases as altitude increases o Increases under water Pressure gradient drives bulk flow o Air moves from high to low pressure o Inspiration pressure in lungs less than atmospheric pressure o Expiration pressure in lungs greater than atmospheric pressure Mechanics of breathing describes mechanisms for creating pressure gradients Increase volume of thoracic cavity o Outward pull on pleura decreases intrapleural pressure which results in an increase in transpulmonary pressure Ribs and sternum depress Decrease volume of thoracic cavity o Normally a passive process Expansion of ribs moves sternum upward and outward Internal intercostals and abdominals contract for active expiration only muscles Diaphragm contraction causes it to flatten and move downward Contraction of external intercostals makes ribs pivot upward and outward expanding the chest wall Collectively thoracic cavity volume increases Outward pull on pleura decreases intrapleural pressure which results in an increase in transpulmonary pressure Alveoli expand decreasing alveolar pressure Air flows into alveoli by bulk flow Factors Affecting Pulmonary Ventilation Lung compliance Ease with which lungs can be stretched o Larger lung compliance Easier to inspire o Smaller change in transpulmonary pressure needed to bring in a given volume of air Airway resistance o Similar to TPR in cardiovascular system Lung Compliance Factors affecting lung compliance o Elasticity More elastic less compliant o Surface tension of lungs o Surface tension force for alveoli to collapse or resist expansion Greater surface tension less compliant A bad thing o Thin layer of fluid lines alveoli Surface tension arises due to attractions between water molecules o http www youtube com watch v Pe12NedfYC0 Surfactant secreted from type II cells o Surfactant detergent that decreases surface tension o Surfactant increases lung compliance o Makes inspiration easier Laplaces s Law P 2T r where T surface tension r radius o Here P is the pressure gradient across alveolar wall At same T smaller r results in greater P and favors collapse Surfactant lowers T to prevent this