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BIOC33/34 Lec 10.docx

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Biological Sciences
Stephen Reid

BIOC33/34 Lec 10. Feb 5/14  Lungs, Thoracic Cavity and Pleura o Lungs sit in the thoracic cavity - comprised of ribs, sternum, intercostal muscles, diaphragm o Diaphragm = major respiratory muscle o Each individual lung is situated within a pleural sac  Pleural sac consists of 2 linings: • Visceral pleura - sits right on top of lung tissue • Parietal pleura - annealed to chest walls; ribs and muscles  In between the two, small pleural space - interpleural fluid. Negative pressure space. Fluid is important to keep these 2 linings together  Important pressure differences o 3 important pressures  Atmospheric pressure (Patm) - subject to change with atmospheric conditions  Alveoli pressure (Palv) - under resting conditions, is the same as atmospheric pressure • Changes over course of inspiration allowing air in and expiration to allow air out • Only manipulate this  Interpleural pressure (Pip) • Palv - Pip = transpulmonary pressure o Pressure driving lung expansion o Get initial decrease in Pip allowing lungs to decrease and air to flow in o ** scheme we are looking at is a bit more nuanced than this initial scheme- purposes of air flow is okay to think about it like this o 2 important pressure differences  Palv – Pip = Transpulmonary pressure • Driving force for lung expansion  Patm – Palv: Driving force for air flow into or out of the lungs  Ideal gas law o 2 components to air flow that are important:  Pressure gradient driving air in and out of lungs. Patm - Palv  Resistance to air flow o When looking at pressure gradient, not changing Patm, changing Palv o Can change Palv in 2 ways:  Changing volume of lungs  Changing amount of air/number of moles of air in lungs o PV=nRT  Rearrange to solve for P  P = nRT/V  Boyle’s law o Over inspiration and expiration, changes in pressure and number of moles of gas  Air flow o Pressure gradient divided by resistance to flow  Air flow = (Patmospheric – Palveolar) / R o Resistance to flow is created by air flowing through larger tubes and through bronchioles then trachioles o Resistance within individual tubes changes as they get smaller and smaller - like blood flow o Diagram on bottom right  Breath volume goes up during inspiration and down during expiration  Alveolar pressure relative to atmospheric pressure • Prior to inspiration = the 2 are equal • Reverses during expiration  Inspiration o Top half of diagram: Alveolar pressure relative to Patm  Goes down first and comes up to equivalency at end of inspiration just before expiration o On top of diagram:  Blue dots are molecules of air  See change in moles in lungs as they are sucked into lungs by atmosphere o During inspiration (initial stages) pressure in alveoli (relative to Patm) decreases -lungs expand and get pulled out by transpulmonary pressure  Transpulmonary pressure increase, causes lungs to expand - lung volume increases o As lung volume increases, alveoli pressure decreases (Ain diagram) - causing increase in Patm - Palv gradient and air gets sucked into lungs o Get change in pressure relationship - instead of going down, it begins to go up because the number of moles of gas in the lung is increasing  Still being taken into the lungs - alveolar pressure is always lower than Patm during inspiratory phase  Gradient for air flow builds up, maximizes and becomes less o PhaseA  Pressure goes down because volume is going up o Phase B  Number of moles of air increases causing alveolar pressure to go up  This occurs until alveolar pressure and Patm are the same  At this stage, the pressure decrease caused by change in volume has been balanced by pressure increase caused by change in # of moles in lungs  airflow STOPS - lose pressure gradient o Lungs are inflated, go into expiratory phase  Expiration o Reverse occurs o Lungs are now expanded and begin to decrease in volume - diaphragm is no longer contracting now moving upwards o Thoracic and chest collapse back in to normal volume - lung volume goes down; as this happens, pressure goes up o Air is being exhaled - number of moles of gas in lungs decreases o Decrease in pressure in latter phase of expiration due to decrease in number of moles of gas o Alveolar pressure increase (from decrease in V in lungs) is balanced out by decrease in pressure from decrease of number of moles of gas o Alveolar pressure = Patm  no more airflow o 2 points of no airflow:  Initial pause between inspiration and expiration  Transition from inspiration to expiration o Majority of pause happens after expiration  Between inspiration and expiration - happens instantaneously  Pressure-volume changes during inspiration o Have neural input to respiratory muscles - diaphragm is the primary muscles innervated by phrenic nerve  Phrenic nerve comes off cervical area and travels down to innervate diaphragm o External intercostal muscles - also used in inspiration, not as important as diaphragm o Have muscles contracting, diaphragm moving downwards, ribs move up and outward and get expansion of chest wall  Pressure- volume changes during inspiration o As the chest wall begins to expand and move outwards, it pulls on interpleural fluids - get a pulling outwards of interpleural space and fluid o Picture it as having a fixed volume of space being pulled apart and this creates a negative pressure in interpleural space  Interpleural pressure decreases due to outward pulling  Pressure- volume changes during inspiration o As interpleural pressure goes down, (as of yet, no change in Palv). Ptp increases  if Palv has not changed and Pip goes down, difference between the two increases (Ptp) o Ptp = pressure causing lungs to expand and increase volume of the lung o As volume of lung goes down, Palv falls o Get a flow of air into lungs and causes Palv to go up; get a feedback which stops the process  Pressure-volume o In this sequence of events, o Start with neural input along phrenic nerve  causes diaphragm to contract, intercostal muscles to contract, ribs move up and out, chest wall expands o Causes an outward pull in interpleural fluid - decrease Pip o Pip decreases  Palv has not changed. Transpulmonary pressure increase  gradient for lung expansion; lung expands  increase in volume of the lungs o From ideal gas law, know when V increases, P goes down o Palv goes down  Patm - Palv pressure gradient increases  gradient for airflow into/out of lungs o Air has flown into lungs and achieve status where the increase in P has gone back to Patm  at pause for inspiration to expiration  Lung compliance o When lungs are expanding and contracting, have a degree of expandability or compliance o Compliance: a measure of the ease of expansion the lungs o Lung Compliance = ΔLung Volume /Δ(Palv – Pip)  Low compliance: any given change in pressure leads to a relatively small change in volume  High compliance: the same change in pressure leads to a relatively large change in volume o There are 3 volumes which are going to be looked at: o TLC = total lung capacity  Total amount of air that can exist in lungs when there is a maximum inspiration and can no longer breathe in o RV = residual volume  Amount of air in lungs after a maximal expiration o FRC = functional residual capacity  Residual volume + air that would be in between a normal expiration and maximum expiration o Lung compliance changes w
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