Lecture 17: Respiratory System PDF

About This Chapter 17.1 The Respiratory System 17.2 Gas Laws 17.3 Ventilation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Respiratory System Bulk Flow Air and blood are both fluids: primary difference between air flow in respiratory system and blood flow in circulator...

About This Chapter 17.1 The Respiratory System 17.2 Gas Laws 17.3 Ventilation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Respiratory System Bulk Flow Air and blood are both fluids: primary difference between air flow in respiratory system and blood flow in circulatory system is that air is less viscous, compressible mixture of gases while blood is a non compressible liquid 1. Flow takes place from regions of higher to lower pressure 2. A muscular pump creates pressure gradients 3. Resistance to air flow is influenced primarily by the diameter of the tubes through which air is flowing Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 17.1 The Respiratory System reaction of oxygen with organic molecules to produce carbon dioxide, water, and energy in • Cellular respiration intracellular the form of ATP • External respiration movement of gases between environment and body’s cell 1. The exchange of air between the atmosphere and the lungs ▪ Ventilation: inspiration and expiration 2. The exchange of O2 & CO2 between the lungs and the blood 3. The transport of O2 & CO2 by the blood 4. The exchange of gases between blood and the cells (can also be called internal respiration) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.1 External respiration Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 17.1 Respiratory System (Structures) 1. Conducting system, or airways – Upper respiratory tract ▪ Mouth, nasal cavity, pharynx, larynx – Lower respiratory tract thoracique portion bc enclosed in thorax ▪ Trachea, 2 primary bronchi, their branches, lungs 2. Alveoli (singular alveolus) - site of gas exchange series of interconnected sacs and their associated pulmonary capillaries Exchange surface where oxygen moves from inhaled air to blood and carbon dioxide moves from blood to air that is about to be exhaled 3. Thoracic cage: bones and muscle of thorax and abdomen ▪ Bones and muscles of the thorax surround the lungs ▪ Spine and rib cage internal and external connecting 12 pairs of ribs ▪ Diaphragm, intercostal muscles, sternocleidomastoids, scalenes and thoracic blood vessels and nerves pass ▪ Pleural sacs each surround a lung esophagus between pleural sacs Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Pleural Sacs Enclose the Lungs • Lungs light, spongy tissue whose volume is occupied mostly by air-filled spaces • Pleura pleural membrane containing several layers of elastic connective tissue and numerous capillaries double-walled pleural sac surrounding each lungs, membranes line inside of thorax and cover outer surface of lungs • Pleural fluid holds together opposing layers of pleural membrane – Lowers friction between membranes – Holds lungs tight against the thoracic wall Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.2(a-b) The Lungs and Thoracic Cavity Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.2(c-d) The Lungs and Thoracic Cavity Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.2(e-f) The Lungs and Thoracic Cavity Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.2(g-h) The Lungs and Thoracic Cavity Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.3 The pleural sac Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.4 Airway branching in the lower respiratory tract Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Airways Connect Lungs to External Environment • • common passageway for food, liquids and air Pharnyx → larynx → trachea (windpipe) tissue bands that vibrate and tighten to create sound when air – Larynx contains vocal cords connective moves past them collapsible passageways with walls of smooth muscle Primary bronchi → bronchioles small bronchioles continue branching until respiratory bronchioles form a transition between airways and exchange epithelium of lung • The airways warm, humidify, and filter inspired air that core body temperature does not change and alveoli are 1. Warming air to body temperature so not damaged by cold air 2. Adding water vapor until air reaches 100% humidity so that the moist exchange in epithelium does not dry out 3. Filtering out foreign material so that they don’t reach alveoli Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Alveoli Are the Site of Gas Exchange • Type I alveolar cells – gas exchange • Type II alveolar cells – produce surfactant • not contain muscle bc muscle fibres would block Connective tissue – elastin and collagen do rapid gas exchange, so lung tissue itself can’t • Close association with capillaries • Pulmonary circulation is high flow, low pressure larger 95% that mixes with thin fluid lining alveoli to aid lungs as they expand during breathing help minimize the amount of fluid present in alveoli by transporting solutes and water out of the alveolar air space contract elastic recoil when lung tissue is stretched – Right ventricle → pulmonary trunk → pulmonary arteries → lungs → pulmonary veins → left atrium – Blood flow through lungs = blood flow through rest of body ▪ Low resistance due to fewer blood vessel length Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.5(a-b) Airway epithelium Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.5(c) Airway epithelium Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 17.2 Gas Laws • Atmospheric pressure in mm Hg • Gases move down pressure gradients • Air is a mixture of gases – Dalton’s law ▪ Total pressure equals sum of all partial pressures (Pgas) • Boyle’s law describes pressure-volume relationships – P1V1 = P2 V2 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.6(c) Gas Laws (2 of 2) In humid air, water vapor “dilutes” the contribution of other gases to the total pressure. Partial Pressures (Pgas) of Atmospheric Gases at 760 mm Hg Gas and its percentage Pgas in dry 25 °C air in air Pgas in 25 °C air, 100% Pgas in 37 °C air, 100% humidity humidity O2 21% 160 mm Hg 155 mm Hg 150 mm Hg CO2 0.03% 0.25 mm Hg 0.24 mm Hg 0.235 mm Hg Water vapour 0 mm Hg 24 mm Hg 47 mm Hg To calculate the partial pressure of a gas in humid air, you must first subtract the water vapor pressure from the total pressure. At 100% humidity and 25 °C, water vapor pressure (PH O ) is 24 mm Hg. 2 Pgas inhumid air =(Patm − PH2O )  %of gas PO2 = (760 − 24)  21% = 155mmHg Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 17.3 Ventilation • Respiratory cycle = 1 inspiration followed by 1 expiration • Lung volumes change during ventilation – Pulmonary function tests use a spirometer • Lung volumes – Tidal volume (VT): volume that moves during a respiratory cycle – Inspiratory reserve volume (IRV): additional volume above tidal volume – Expiratory reserve volume (ERV): forcefully exhaled after the end of a normal expiration – Residual volume (RV): volume of air in the respiratory system after maximal exhalation • Lung Capacity – Vital capacity (VC) = IRV + ERV + VT – Total lung capacity ( TLC ) = IRV + ERV + VT Vt + IRV ERV + RV – Inspiratory capacity and functional reserve capactty Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.7(a) Pulmonary function tests Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.7(b) Pulmonary function tests Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.8 Movement of the thoracic cage and diaphragm during breathing External intercostal muscle; scalene Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved During ventilation, Air Flows because of Pressure Gradients • Flow  P R air flows in response to a pressure gradient and decreases as distance of system to flow increases • Inspiration occurs when alveolar pressure decreases – Time 0 ▪ When pressures are equal there is no air flow – Time 0-2 sec: inspiration • Expiration occurs when alveolar pressure increases – Time 2-4 sec: expiration – Time 4 sec ▪ Passive vs. active expiration voluntary exhalations and when ventilation exceeds 30/40 breaths per minute (normal resting one is 12-20 breaths per minute for an adult) uses internal intercostal muscle and abdominal muscle (these 2 are expiratory muscles), which are not used during inspiration Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.9 Pressure changes during quiet breathing Vt Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.10 Subatmospheric pressure in the pleural cavity keeps the lungs inflated Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Lung Compliance and Elastance • Compliance: ability to stretch – High compliance ▪ Stretches easily – Low compliance ▪ Requires more force ▪ Restrictive lung diseases – Fibrotic lung diseases (fibrosis) – Inadequate surfactant production (NRDS) • Elastance: ability to return to resting volume when stretching force is released Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Surfactant Decreases the Work of Breathing • Law of LaPlace pressure inside the smaller bubble > larger : pressure surface tension of fluid – P = 2T r PT:r: radius of bubble If 2 bubbles have different diameters but are formed by fluids with same surface tension, • Surfactants: surface active agents – Disrupt cohesive force of water by substituting themselves for water at surface dipalmitoylphosphatidylcholi (secreted by type II cells in alveolar air – Mixture containing proteins and phospholipids nealveolar space) – More concentrated in smaller alveoli • Premature babies – Inadequate surfactant concentrations – Newborn respiratory distress syndrome (NRDS) Babies who are born prematurely without adequate concentrations of surfactant in their alveoli Low compliance lungs Alveoli that collapse each time they exhale Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.11 Law of LaPlace Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 17.2 Factors That Affect Airway Resistance Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Airway Diameter Determines Airway Resistance • Airway diameter – Wider airways have less resistance RL resistance length – R  Lη r 4 L:n: system’s viscosity of substance flowing through system r: radius of tubes in system decrease amount of fresh air that reaches • Bronchoconstriction increases resistance and the alveoli – Parasympathetic carbon dioxide in airways: primary paracrine molecule that affects bronchiolar diabetes Increased CO2 in expired air relaxes bronchiolar smooth muscle and causes bronchodilatation • Bronchodilation decreases resistance – Sympathetic: 2 receptors on smooth muscles relax in response to epinephrine Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Rate and Depth of Breathing Determine the Efficiency of Breathing • Total pulmonary ventilation – Volume of air moved in and out of lungs per minute – Ventilationrate  tidal volume 6 L/min • Anatomic dead space conducting airways of trachea and bronchi do not exchange gases with blood • Alveolar ventilation – More accurate – Ventilationrate  ( tidal volume − dead space ) 4.2 L/min as deeply and quickly as possible may increase total pulmonary ventilation to as much as 170 L/min • Maximum voluntary ventilation breaving Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.12(a) Ventilation (a) Total pulmonary ventilation is greater than alveolar ventilation because of dead space. Total pulmonary ventilation: Total pulmonary ventilation = ventilation rate × tidal volume (VT ) For example: 12 breaths / min × 500 mL breath = 6000 mL / min Alveolar ventilation: Alveolar ventilation is a better indication of how much fresh air reaches the alveoli. Fresh air remaining in the dead space does not get to the alveoli. Alveolar ventilation = ventilation rate × (VT -dead space volume VD ) If dead space is 150 mL: 12 breaths / min  (500 − 150 mL) = 4200 mL / min Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.12(b) Ventilation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 17.4 Normal Ventilation Values in Pulmonary Medicine Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Alveolar Gas Composition Varies Little during Normal Breathing • O2 entering alveoli  O2 entering the blood • Fresh air into lungs  10% total lung volume at the end of inspiration • Ventilation and alveolar blood flow are matched – Ensures efficiency of gas exchange between alveoli and capillaries Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.13 Alveolar gases Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 17.14 Local Control Mechanisms Attempt to Match Ventilation and Perfusion (d) Bronchiole diameter is mediated primarily by CO2 levels in exhaled air passing through them. Local Control of Arterioles and Bronchioles by Oxygen and Carbon Dioxide Gas Composition increases PCO2 Bronchioles Pulmonary Arteries Dilate (Constrict)* Systemic Arteries Dilate PCO2 decreases Constrict (Dilate) Constrict PO2 increases (Dilate) Constrict Constrict Dilate (Constrict) PO2 decreases (Dilate) *Parentheses indicate weak responses. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Key words • cellular respiration, external respiration, ventilation, inspiration, expiration, conducting system, airways, alveolus (alveoli), upper respiratory tract, lower respiratory tract, diaphragm, intercostal muscles, pleural sacs, pleura, pleural fluid, pharynx, larynx, trachea, bronchi, bronchioles, respiratory bronchioles, CFTR channel, goblet cells, Dalton’s law, Boyle’s law, tidal volume (VT), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), residual volume (RV), inspiratory muscles, external intercostals, passive expiration, active expiration, expiratory muscles, visceral pleura, parietal pleura, intrapleural pressure, total pulmonary ventilation (minute volume), anatomic dead space, alveolar ventilation. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved