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UNCG KIN 292 - Chapter 16: The Respiratory System- Pulmonary Ventilation

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KIN 292 1nd Edition Lecture 28 Outline of Last LectureChapter 15 continuedOutline of Current LectureI. 16.1 Overview of Respiratory FunctionII. 16.2 Anatomy of the Respiratory SystemIII. 16.3 Forces for Pulmonary VentilationIV. 16.4 Factors Affecting Pulmonary VentilationV. 16.5 Clinical Significance of Respiratory Volumes and Air FlowsCurrent Lecture- External respiration o Pulmonary ventilationo Exchange between lungs and blood in pulmonary circulationo Transportation in bloodo 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 boozeo 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 brainThe Respiratory TractThese 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 zoneo Air passageway: 150 mL in volume (dead space), no gas exchangeo Increases air temperature to body temperatureo Humidifies air- Epithelium of the conducting zoneo Goblet cells Secrete mucus to trap foreign particleso Ciliated cells Cilia move mucus + particles toward mouth - Mucus escalatoro Mucus accumulation increases infections and growth of bacteriao 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 mucuselevator- 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 mL16.3 Forces of Pulmonary Ventilation: Pulmonary pressures- Atmospheric pressure = Patmo 760 mmHg at sea level. Other pressures often expressed relative to Patm, so it is set at 0- Intra-alveolar pressure = Palvo Pressure of air in alveoli- Intrapleural pressure = Pipo Pressure inside pleural sac.- Transpulmonary pressure = Palv – Pipo Distending pressure across the lung wall- Intrapleural pressure - Pressure inside pleural sac.o Always negative under normal conditions and less than Palvo Varies with respiration phase. Rest, -4 mm Hgo Negative due to elasticity in lungs and chest wallo Lungs recoil inward as chest wall recoils outwardo Opposing forces pull on intrapleural spaceo Surface tension of intrapleural fluid prevents wall and lungs from pulling apart- Transpulmonary pressure and alveolio Transpulmonary pressure = difference between Palv and Pipo It is the distending pressure across the lung wallo Transpulmonary pressure increases during inspiration causing lungs to expand, increasing volume of alveoliPneumothorax- 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 inflatedMechanics of Breathing- Forces for air flowo Force for flow = pressure gradient (same as with blood flow)o Atmospheric pressure remains constant (during breathing cycle)o Thus alveolar pressure changes affect gradientso Boyle's law: pressure is inversely related to volumeo Can change alveolar pressure by changing its volumeo 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 levelo Decreases as altitude increaseso Increases under water- Pressure gradient drives bulk flowo Air moves from high to low pressureo Inspiration: pressure in lungs less than atmospheric pressureo Expiration: pressure in lungs greater than atmospheric pressure- Mechanics of breathing describes mechanisms for creating pressure gradients- Increase volume of thoracic cavityo Outward pull on pleura decreases intrapleural pressure, which results in an increase in transpulmonary pressure- Ribs and sternum depress. Decrease volume of thoracic cavityo 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 flowFactors Affecting Pulmonary Ventilation- Lung compliance - Ease with which lungs can be stretchedo Larger lung compliance = Easier to inspireo Smaller change in transpulmonary pressure needed to bring in a given volume of air- Airway resistanceo Similar to TPR in cardiovascular systemLung Compliance- Factors affecting lung complianceo Elasticity More elastic  less complianto Surface tension of lungso Surface tension: force for alveoli to collapse or resist expansion. Greater surface tension  less compliant. A bad thingo Thin layer of fluid lines alveoli. Surface tension arises due to attractions between water moleculeso http://www.youtube.com/watch?v=Pe12NedfYC0- Surfactant secreted from type II cellso Surfactant: detergent that decreases surface tensiono Surfactant increases lung complianceo Makes inspiration easier- Laplaces’s Law P = 2T/r where T = surface tension, r =radius.o Here P is the


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UNCG KIN 292 - Chapter 16: The Respiratory System- Pulmonary Ventilation

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