Chapter 23
Chapter 23 The Respiratory SystemThe Respiratory SystemLearning Outcomes23-1 Describe the primary functions of the respiratory system, and explain how the delicate respiratory exchange surfaces are protected from pathogens, debris, and other hazards.23-2 Identify the organs of the upper respiratory system, and describe their functions.23-3Describe the structure of the larynx, and discuss its roles in normal breathing and in sound production.The Respiratory SystemLearning Outcomes23-4 Discuss the structure of the extrapulmonary airways.23-5 Describe the superficial anatomy of the lungs, the structure of a pulmonary lobule, and the functional anatomy of alveoli.23-6 Define and compare the processes of external respiration and internal respiration.The Respiratory SystemLearning Outcomes23-7 Summarize the physical principles controlling the movement of air into and out of the lungs, and describe the origins and actions of the muscles responsible for respiratory movements.23-8 Summarize the physical principles governing the diffusion of gases into and out of the blood and body tissues.23-9Describe the structure and function of hemoglobin, and the transport of oxygen and carbon dioxide in the blood.The Respiratory SystemLearning Outcomes23-10List the factors that influence respiration rate, and discuss reflex respiratory activity and the brain centers involved in the control of respiration.23-11Describe age-related changes in the respiratory system.23-12Give examples of interactions between the respiratory system and other organ systems studied so far.An Introduction to the Respiratory SystemThe Respiratory System Cells produce energyFor maintenance, growth, defense, and divisionThrough mechanisms that use oxygen and produce carbon dioxideAn Introduction to the Respiratory SystemOxygen Is obtained from the air by diffusion across delicate exchange surfaces of lungsIs carried to cells by the cardiovascular system, which also returns carbon dioxide to the lungs 23-1 Components of the Respiratory SystemFive Functions of the Respiratory SystemProvides extensive gas exchange surface area between air and circulating bloodMoves air to and from exchange surfaces of lungsProtects respiratory surfaces from outside environmentProduces soundsParticipates in olfactory sense23-1 Components of the Respiratory SystemOrganization of the Respiratory System The respiratory system is divided into:Upper respiratory system – above the larynxLower respiratory system – below the larynx23-1 Components of the Respiratory SystemThe Respiratory Tract Consists of a conducting portionFrom nasal cavity to terminal bronchiolesConsists of a respiratory portionThe respiratory bronchioles and alveoliAlveoli Are air-filled pockets within the lungsWhere all gas exchange takes place23-1 Components of the Respiratory SystemThe Respiratory Epithelium For gases to exchange efficiently:Alveoli walls must be very thin (<1 ?m) Surface area must be very great (about 35 times the surface area of the body)23-1 Components of the Respiratory SystemThe Respiratory Mucosa Consists of:An epithelial layerAn areolar layer called the lamina propriaLines the conducting portion of respiratory system 23-1 Components of the Respiratory SystemThe Lamina Propria Underlying layer of areolar tissue that supports the respiratory epitheliumIn the upper respiratory system, trachea, and bronchiIt contains mucous glands that secrete onto epithelial surfaceIn the conducting portion of lower respiratory systemIt contains smooth muscle cells that encircle lumen of bronchioles23-1 Components of the Respiratory SystemStructure of Respiratory Epithelium Pseudostratified ciliated columnar epithelium with numerous mucous cells Nasal cavity and superior portion of the pharynxStratified squamous epithelium Inferior portions of the pharynx Pseudostratified ciliated columnar epitheliumSuperior portion of the lower respiratory systemCuboidal epithelium with scattered cilia Smaller bronchioles23-1 Components of the Respiratory SystemAlveolar Epithelium Is a very delicate, simple squamous epitheliumContains scattered and specialized cellsLines exchange surfaces of alveoli23-1 Components of the Respiratory SystemThe Respiratory Defense System Consists of a series of filtration mechanismsRemoves particles and pathogens23-1 Components of the Respiratory SystemComponents of the Respiratory Defense System Mucous cells and mucous glandsProduce mucus that bathes exposed surfacesCiliaSweep debris trapped in mucus toward the pharynx (mucus escalator)Filtration in nasal cavity removes large particlesAlveolar macrophages engulf small particles that reach lungs 23-2 Upper Respiratory TractThe Nose Air enters the respiratory systemThrough nostrils or external naresInto nasal vestibule Nasal hairsAre in nasal vestibule Are the first particle filtration system23-2 Upper Respiratory TractThe Nasal Cavity The nasal septumDivides nasal cavity into left and rightSuperior portion of nasal cavity is the olfactory regionProvides sense of smellMucous secretions from paranasal sinus and tearsClean and moisten the nasal cavity23-2 Upper Respiratory TractAir Flow From vestibule to internal naresThrough superior, middle, and inferior meatusesMeatuses are constricted passageways that produce air turbulenceWarm and humidify incoming airTrap particles23-2 Upper Respiratory TractThe Palates Hard palateForms floor of nasal cavitySeparates nasal and oral cavitiesSoft palateExtends posterior to hard palateDivides superior nasopharynx from lower pharynx23-2 Upper Respiratory TractAir FlowNasal cavity opens into nasopharynx through internal naresThe Nasal MucosaWarms and humidifies inhaled air for arrival at lower respiratory organs Breathing through mouth bypasses this important step23-2 Upper Respiratory TractThe Pharynx A chamber shared by digestive and respiratory systemsExtends from internal nares to entrances to larynx and esophagusDivided into three partsThe nasopharynxThe oropharynxThe laryngopharynx23-2 Upper Respiratory TractThe Nasopharynx Superior portion of pharynxContains pharyngeal tonsils and openings to left and right auditory tubesThe Oropharynx Middle portion of pharynxCommunicates with oral cavityThe Laryngopharynx Inferior portion of pharynxExtends from hyoid bone to entrance of larynx and esophagus23-3 The LarynxAir FlowFrom the pharynx enters the larynxA cartilaginous structure that surrounds the glottis, which is a narrow opening23-3 The LarynxCartilages of the Larynx Three large, unpaired cartilages form the larynx Thyroid cartilage Cricoid cartilage Epiglottis23-3 The LarynxThe Thyroid Cartilage Is hyaline cartilageForms anterior and lateral walls of larynxAnterior surface called laryngeal prominence, or Adam’s appleLigaments attach to hyoid bone, epiglottis, and laryngeal cartilages23-3 The LarynxThe Cricoid Cartilage Is hyaline cartilageForms posterior portion of larynxLigaments attach to first tracheal cartilageArticulates with arytenoid cartilages23-3 The LarynxThe Epiglottis Composed of elastic cartilageLigaments attach to thyroid cartilage and hyoid bone23-3 The LarynxCartilage Functions Thyroid and cricoid cartilages support and protect:The glottis The entrance to tracheaDuring swallowing:The larynx is elevatedThe epiglottis folds back over glottisPrevents entry of food and liquids into respiratory tract23-3 The LarynxThe Larynx Contains Three Pairs of Smaller Hyaline Cartilages Arytenoid cartilages Corniculate cartilages Cuneiform cartilages23-3 The LarynxCartilage Functions Corniculate and arytenoid cartilages function in:Opening and closing of glottisProduction of sound23-3 The LarynxLigaments of the Larynx Vestibular ligaments and vocal ligamentsExtend between thyroid cartilage and arytenoid cartilagesAre covered by folds of laryngeal epithelium that project into glottis23-3 The LarynxThe Vestibular LigamentsLie within vestibular foldsWhich protect delicate vocal foldsSound Production Air passing through glottisVibrates vocal foldsProduces sound waves23-3 The LarynxSound ProductionSound is varied by:Tension on vocal foldsVocal folds involved with sound are known as vocal cordsVoluntary muscles (position arytenoid cartilage relative to thyroid cartilage) Speech is produced by:PhonationSound production at the larynxArticulationModification of sound by other structures23-3 The LarynxThe Laryngeal Musculature The larynx is associated with:Muscles of neck and pharynxIntrinsic musclesControl vocal foldsOpen and close glottis23-4 The Trachea The TracheaAlso called the windpipeExtends from the cricoid cartilage into mediastinumWhere it branches into right and left pulmonary bronchiThe submucosa Beneath mucosa of tracheaContains mucous glands23-4 The Trachea The Tracheal Cartilages 15–20 tracheal cartilagesStrengthen and protect airwayDiscontinuous where trachea contacts esophagusEnds of each tracheal cartilage are connected by:An elastic ligament and trachealis muscle 23-4 The Trachea The Primary Bronchi Right and Left Primary BronchiSeparated by an internal ridge (the carina)The Right Primary BronchusIs larger in diameter than the leftDescends at a steeper angle23-4 The Trachea The Primary BronchiHilum Where pulmonary nerves, blood vessels, lymphatics enter lungAnchored in meshwork of connective tissueThe root of the lungComplex of connective tissues, nerves, and vessels in hilumAnchored to the mediastinum23-5 The LungsThe Lungs Left and right lungsAre in left and right pleural cavitiesThe baseInferior portion of each lung rests on superior surface of diaphragmLobes of the lungs Lungs have lobes separated by deep fissures 23-5 The LungsLobes and Surfaces of the LungsThe right lung has three lobes Superior, middle, and inferiorSeparated by horizontal and oblique fissuresThe left lung has two lobes Superior and inferiorSeparated by an oblique fissure23-5 The LungsLung Shape Right lungIs wider Is displaced upward by liverLeft lungIs longer Is displaced leftward by the heart forming the cardiac notch23-5 The LungsThe BronchiThe Bronchial Tree Is formed by the primary bronchi and their branchesExtrapulmonary BronchiThe left and right bronchi branches outside the lungsIntrapulmonary BronchiBranches within the lungs23-5 The LungsA Primary Bronchus Branches to form secondary bronchi (lobar bronchi)One secondary bronchus goes to each lobeSecondary BronchiBranch to form tertiary bronchi (segmental bronchi)Each segmental bronchusSupplies air to a single bronchopulmonary segment23-5 The LungsBronchopulmonary SegmentsThe right lung has 10The left lung has 8 or 9Bronchial StructureThe walls of primary, secondary, and tertiary bronchiContain progressively less cartilage and more smooth muscleIncreased smooth muscle tension affects airway constriction and resistance23-5 The LungsBronchitis Inflammation of bronchial wallsCauses constriction and breathing difficulty23-5 The LungsThe Bronchioles Each tertiary bronchus branches into multiple bronchiolesBronchioles branch into terminal bronchioles One tertiary bronchus forms about 6500 terminal bronchiolesBronchiole StructureBronchiolesHave no cartilageAre dominated by smooth muscle23-5 The LungsAutonomic Control Regulates smooth muscleControls diameter of bronchiolesControls airflow and resistance in lungs23-5 The LungsBronchodilationDilation of bronchial airwaysCaused by sympathetic ANS activation Reduces resistanceBronchoconstriction Constricts bronchiCaused by: Parasympathetic ANS activationHistamine release (allergic reactions)23-5 The LungsAsthma Excessive stimulation and bronchoconstriction Stimulation severely restricts airflow23-5 The LungsPulmonary Lobules TrabeculaeFibrous connective tissue partitions from root of lungContain supportive tissues and lymphatic vesselsBranch repeatedlyDivide lobes into increasingly smaller compartmentsPulmonary lobules are divided by the smallest trabecular partitions (interlobular septa) 23-5 The LungsPulmonary LobulesEach terminal bronchiole delivers air to a single pulmonary lobuleEach pulmonary lobule is supplied by pulmonary arteries and veins Each terminal bronchiole branches to form several respiratory bronchioles, where gas exchange takes place23-5 The LungsAlveolar Ducts and AlveoliRespiratory bronchioles are connected to alveoli along alveolar ductsAlveolar ducts end at alveolar sacs Common chambers connected to many individual alveoli Each alveolus has an extensive network of capillariesSurrounded by elastic fibers23-5 The LungsAlveolar Epithelium Consists of simple squamous epitheliumConsists of thin, delicate type I pneumocytes patrolled by alveolar macrophages (dust cells)Contains type II pneumocytes (septal cells) that produce surfactant23-5 The LungsSurfactant Is an oily secretionContains phospholipids and proteinsCoats alveolar surfaces and reduces surface tension23-5 The LungsRespiratory Distress SyndromeDifficult respirationDue to alveolar collapse Caused when type II pneumocytes do not produce enough surfactant Respiratory MembraneThe thin membrane of alveoli where gas exchange takes place23-5 The LungsThree Layers of the Respiratory MembraneSquamous epithelial cells lining the alveolusEndothelial cells lining an adjacent capillaryFused basement membranes between the alveolar and endothelial cells23-5 The LungsDiffusionAcross respiratory membrane is very rapidBecause distance is short Gases (O2 and CO2) are lipid solubleInflammation of Lobules Also called pneumoniaCauses fluid to leak into alveoliCompromises function of respiratory membrane23-5 The LungsBlood Supply to the LungsRespiratory exchange surfaces receive bloodFrom arteries of pulmonary circuitA capillary network surrounds each alveolusAs part of the respiratory membraneBlood from alveolar capillariesPasses through pulmonary venules and veinsReturns to left atriumAlso site of angiotensin-converting enzyme (ACE)23-5 The LungsBlood Supply to the Lungs Capillaries supplied by bronchial arteriesProvide oxygen and nutrients to tissues of conducting passageways of lung Venous blood bypasses the systemic circuit and flows into pulmonary veins23-5 The LungsBlood Pressure In pulmonary circuit is low (30 mm Hg)Pulmonary vessels are easily blocked by blood clots, fat, or air bubblesCausing pulmonary embolism23-5 The LungsThe Pleural Cavities and Pleural Membranes Two pleural cavitiesAre separated by the mediastinumEach pleural cavity:Holds a lung Is lined with a serous membrane (the pleura)23-5 The LungsThe Pleura Consists of two layers Parietal pleura Visceral pleuraPleural fluidLubricates space between two layers23-6 Introduction to Gas ExchangeRespiration Refers to two integrated processes External respirationIncludes all processes involved in exchanging O2 and CO2 with the environment Internal respirationResult of cellular respirationInvolves the uptake of O2 and production of CO2 within individual cells 23-6 Introduction to Gas ExchangeThree Processes of External Respiration Pulmonary ventilation (breathing) Gas diffusionAcross membranes and capillaries Transport of O2 and CO2Between alveolar capillariesBetween capillary beds in other tissues23-6 Introduction to Gas ExchangeAbnormal External Respiration Is DangerousHypoxiaLow tissue oxygen levelsAnoxiaComplete lack of oxygen23-7 Pulmonary VentilationPulmonary Ventilation Is the physical movement of air in and out of respiratory tractProvides alveolar ventilationThe Movement of AirAtmospheric pressureThe weight of airHas several important physiological effects23-7 Pulmonary VentilationGas Pressure and VolumeBoyle’s Law Defines the relationship between gas pressure and volume P = 1/VIn a contained gas:External pressure forces molecules closer togetherMovement of gas molecules exerts pressure on container23-7 Pulmonary VentilationPressure and Airflow to the LungsAir flows from area of higher pressure to area of lower pressure A Respiratory Cycle Consists of: An inspiration (inhalation)An expiration (exhalation)23-7 Pulmonary VentilationPulmonary Ventilation Causes volume changes that create changes in pressureVolume of thoracic cavity changesWith expansion or contraction of diaphragm or rib cage23-7 Pulmonary VentilationComplianceAn indicator of expandabilityLow compliance requires greater forceHigh compliance requires less forceFactors That Affect ComplianceConnective tissue structure of the lungsLevel of surfactant productionMobility of the thoracic cage23-7 Pulmonary VentilationPressure Changes during Inhalation and ExhalationCan be measured inside or outside the lungsNormal atmospheric pressure 1 atm = 760 mm Hg23-7 Pulmonary VentilationThe Intrapulmonary Pressure Also called intra-alveolar pressureIs relative to atmospheric pressureIn relaxed breathing, the difference between atmospheric pressure and intrapulmonary pressure is smallAbout 1 mm Hg on inhalation or 1 mm Hg on exhalation 23-7 Pulmonary VentilationMaximum Intrapulmonary Pressure Maximum straining, a dangerous activity, can increase rangeFrom 30 mm Hg to 100 mm Hg23-7 Pulmonary VentilationThe Intrapleural Pressure Pressure in space between parietal and visceral pleura Averages 4 mm HgMaximum of 18 mm HgRemains below atmospheric pressure throughout respiratory cycle 23-7 Pulmonary VentilationThe Respiratory Cycle Cyclical changes in intrapleural pressure operate the respiratory pumpWhich aids in venous return to heartTidal Volume (VT)Amount of air moved in and out of lungs in a single respiratory cycle 23-7 Pulmonary VentilationInjury to the Chest WallPneumothorax allows air into pleural cavityAtelectasis (also called a collapsed lung) is a result of pneumothorax 23-7 Pulmonary VentilationThe Respiratory Muscles Most important are:The diaphragm External intercostal muscles of the ribsAccessory respiratory musclesActivated when respiration increases significantly23-7 Pulmonary VentilationThe Mechanics of Breathing InhalationAlways activeExhalationActive or passive23-7 Pulmonary VentilationMuscles Used in InhalationDiaphragmContraction draws air into lungs75 percent of normal air movementExternal intercostal musclesAssist inhalation25 percent of normal air movementAccessory muscles assist in elevating ribsSternocleidomastoidSerratus anteriorPectoralis minorScalene muscles23-7 Pulmonary VentilationMuscles Used in ExhalationInternal intercostal and transversus thoracis musclesDepress the ribsAbdominal musclesCompress the abdomenForce diaphragm upward23-7 Pulmonary VentilationModes of Breathing Respiratory movements are classifiedBy pattern of muscle activityQuiet breathing Forced breathing23-7 Pulmonary VentilationQuiet Breathing (Eupnea) Involves active inhalation and passive exhalationDiaphragmatic breathing or deep breathingIs dominated by diaphragm Costal breathing or shallow breathingIs dominated by rib cage movements23-7 Pulmonary VentilationElastic Rebound When inhalation muscles relaxElastic components of muscles and lungs recoilReturning lungs and alveoli to original position 23-7 Pulmonary VentilationForced Breathing (Hyperpnea) Involves active inhalation and exhalationAssisted by accessory musclesMaximum levels occur in exhaustion23-7 Pulmonary VentilationRespiratory Rates and Volumes Respiratory system adapts to changing oxygen demands by varying:The number of breaths per minute (respiratory rate)The volume of air moved per breath (tidal volume) 23-7 Pulmonary VentilationThe Respiratory Minute Volume (VE)Amount of air moved per minuteIs calculated by:respiratory rate ? tidal volumeMeasures pulmonary ventilation23-7 Pulmonary VentilationAlveolar Ventilation (VA)Only a part of respiratory minute volume reaches alveolar exchange surfacesVolume of air remaining in conducting passages is anatomic dead spaceAlveolar ventilation is the amount of air reaching alveoli each minuteCalculated as:(tidal volume anatomic dead space) ? respiratory rate23-7 Pulmonary VentilationAlveolar Gas Content Alveoli contain less O2, more CO2 than atmospheric airBecause air mixes with exhaled air23-7 Pulmonary VentilationRelationships among VT, VE, and VADetermined by respiratory rate and tidal volumeFor a given respiratory rate:Increasing tidal volume increases alveolar ventilation rateFor a given tidal volume:Increasing respiratory rate increases alveolar ventilation23-7 Pulmonary VentilationRespiratory Performance and Volume RelationshipsTotal lung volume is divided into a series of volumes and capacities useful in diagnosing problemsFour Pulmonary Volumes Resting tidal volume (Vt) Expiratory reserve volume (ERV) Residual volume Inspiratory reserve volume (IRV)23-7 Pulmonary VentilationResting Tidal Volume (Vt)In a normal respiratory cycleExpiratory Reserve Volume (ERV)After a normal exhalationResidual VolumeAfter maximal exhalationMinimal volume (in a collapsed lung)Inspiratory Reserve Volume (IRV)After a normal inspiration23-7 Pulmonary VentilationFour Calculated Respiratory Capacities Inspiratory capacity Tidal volume + inspiratory reserve volume Functional residual capacity (FRC) Expiratory reserve volume + residual volume Vital capacity Expiratory reserve volume + tidal volume + inspiratory reserve volume23-7 Pulmonary VentilationFour Calculated Respiratory Capacities Total lung capacity Vital capacity + residual volumePulmonary Function Tests Measure rates and volumes of air movements23-8 Gas ExchangeGas Exchange Occurs between blood and alveolar airAcross the respiratory membraneDepends on: Partial pressures of the gases Diffusion of molecules between gas and liquid23-8 Gas ExchangeThe Gas Laws Diffusion occurs in response to concentration gradientsRate of diffusion depends on physical principles, or gas lawsFor example, Boyle’s law23-8 Gas ExchangeDalton’s Law and Partial PressuresComposition of Air Nitrogen (N2) is about 78.6 percentOxygen (O2) is about 20.9 percentWater vapor (H2O) is about 0.5 percentCarbon dioxide (CO2) is about 0.04 percent23-8 Gas ExchangeDalton’s Law and Partial PressuresAtmospheric pressure (760 mm Hg)Produced by air molecules bumping into each otherEach gas contributes to the total pressureIn proportion to its number of molecules (Dalton’s law)23-8 Gas ExchangePartial Pressure The pressure contributed by each gas in the atmosphereAll partial pressures together add up to 760 mm Hg23-8 Gas ExchangeDiffusion between Liquids and GasesHenry’s Law When gas under pressure comes in contact with liquid:Gas dissolves in liquid until equilibrium is reachedAt a given temperature:Amount of a gas in solution is proportional to partial pressure of that gasThe actual amount of a gas in solution (at given partial pressure and temperature): Depends on the solubility of that gas in that particular liquid23-8 Gas ExchangeSolubility in Body Fluids CO2 is very solubleO2 is less solubleN2 has very low solubility23-8 Gas ExchangeNormal Partial Pressures In pulmonary vein plasmaPCO2 = 40 mm HgPO2 = 100 mm HgPN2 = 573 mm Hg23-8 Gas ExchangeDiffusion and Respiratory FunctionDirection and rate of diffusion of gases across the respiratory membrane Determine different partial pressures and solubilities23-8 Gas ExchangeFive Reasons for Efficiency of Gas ExchangeSubstantial differences in partial pressure across the respiratory membraneDistances involved in gas exchange are shortO2 and CO2 are lipid solubleTotal surface area is largeBlood flow and airflow are coordinated23-8 Gas ExchangePartial Pressures in Alveolar Air and Alveolar CapillariesBlood arriving in pulmonary arteries has:Low PO2 High PCO2 The concentration gradient causes:O2 to enter bloodCO2 to leave bloodRapid exchange allows blood and alveolar air to reach equilibrium23-8 Gas ExchangePartial Pressures in the Systemic CircuitOxygenated blood mixes with deoxygenated blood from conducting passageways Lowers the PO2 of blood entering systemic circuit (drops to about 95 mm Hg)23-8 Gas ExchangePartial Pressures in the Systemic CircuitInterstitial Fluid PO2 40 mm Hg PCO2 45 mm HgConcentration gradient in peripheral capillaries is opposite of lungsCO2 diffuses into bloodO2 diffuses out of blood23-9 Gas TransportGas Pickup and Delivery Blood plasma cannot transport enough O2 or CO2 to meet physiological needs Red Blood Cells (RBCs) Transport O2 to, and CO2 from, peripheral tissuesRemove O2 and CO2 from plasma, allowing gases to diffuse into blood23-9 Gas TransportOxygen Transport O2 binds to iron ions in hemoglobin (Hb) moleculesIn a reversible reactionNew molecule is called oxyhemoglobin (HbO2)Each RBC has about 280 million Hb moleculesEach binds four oxygen molecules23-9 Gas TransportHemoglobin Saturation The percentage of heme units in a hemoglobin molecule that contain bound oxygen Environmental Factors Affecting Hemoglobin PO2 of bloodBlood pHTemperatureMetabolic activity within RBCs23-9 Gas TransportOxygen–Hemoglobin Saturation Curve A graph relating the saturation of hemoglobin to partial pressure of oxygenHigher PO2 results in greater Hb saturationCurve rather than a straight line because Hb changes shape each time a molecule of O2 is boundEach O2 bound makes next O2 binding easierAllows Hb to bind O2 when O2 levels are low23-9 Gas TransportOxygen Reserves O2 diffusesFrom peripheral capillaries (high PO2)Into interstitial fluid (low PO2)Amount of O2 released depends on interstitial PO2 Up to 3/4 may be reserved by RBCs23-9 Gas TransportCarbon Monoxide CO from burning fuelsBinds strongly to hemoglobinTakes the place of O2Can result in carbon monoxide poisoning23-9 Gas TransportThe Oxygen–Hemoglobin Saturation Curve Is standardized for normal blood (pH 7.4, 37C)When pH drops or temperature rises:More oxygen is releasedCurve shifts to rightWhen pH rises or temperature drops:Less oxygen is releasedCurve shifts to left23-9 Gas TransportHemoglobin and pHBohr effect is the result of pH on hemoglobin-saturation curveCaused by CO2CO2 diffuses into RBCAn enzyme, called carbonic anhydrase, catalyzes reaction with H2OProduces carbonic acid (H2CO3)Dissociates into hydrogen ion (H+) and bicarbonate ion (HCO3–)Hydrogen ions diffuse out of RBC, lowering pH23-9 Gas TransportHemoglobin and TemperatureTemperature increase = hemoglobin releases more oxygenTemperature decrease = hemoglobin holds oxygen more tightlyTemperature effects are significant only in active tissues that are generating large amounts of heatFor example, active skeletal muscles23-9 Gas TransportHemoglobin and BPG2,3-bisphosphoglycerate (BPG) RBCs generate ATP by glycolysisForming lactic acid and BPGBPG directly affects O2 binding and release More BPG, more oxygen released23-9 Gas TransportBPG Levels BPG levels rise:When pH increasesWhen stimulated by certain hormonesIf BPG levels are too low:Hemoglobin will not release oxygen23-9 Gas TransportFetal Hemoglobin The structure of fetal hemoglobinDiffers from that of adult HbAt the same PO2:Fetal Hb binds more O2 than adult HbWhich allows fetus to take O2 from maternal blood23-9 Gas TransportCarbon Dioxide Transport (CO2) Is generated as a by-product of aerobic metabolism (cellular respiration)CO2 in the bloodstream can be carried three waysConverted to carbonic acidBound to hemoglobin within red blood cellsDissolved in plasma23-9 Gas TransportCarbonic Acid Formation70 percent is transported as carbonic acid (H2CO3)Which dissociates into H+ and bicarbonate (HCO3–)Hydrogen ions bind to hemoglobinBicarbonate Ions Move into plasma by an exchange mechanism (the chloride shift) that takes in Cl– ions without using ATP23-9 Gas TransportCO2 Binding to Hemoglobin23 percent is bound to amino groups of globular proteins in Hb moleculeForming carbaminohemoglobinTransport in Plasma7 percent is transported as CO2 dissolved in plasma23-10 Control of RespirationPeripheral and Alveolar Capillaries Maintain balance during gas diffusion by: Changes in blood flow and oxygen deliveryChanges in depth and rate of respiration23-10 Control of RespirationLocal Regulation of Gas Transport and Alveolar FunctionRising PCO2 levels Relax smooth muscle in arterioles and capillariesIncrease blood flowCoordination of lung perfusion and alveolar ventilationShifting blood flowPCO2 levelsControl bronchoconstriction and bronchodilation23-10 Control of RespirationThe Respiratory Centers of the Brain When oxygen demand rises:Cardiac output and respiratory rates increase under neural controlHave both voluntary and involuntary components23-10 Control of RespirationThe Respiratory Centers of the Brain Voluntary centers in cerebral cortex affect:Respiratory centers of pons and medulla oblongataMotor neurons that control respiratory musclesThe Respiratory Centers Three pairs of nuclei in the reticular formation of medulla oblongata and ponsRegulate respiratory musclesIn response to sensory information via respiratory reflexes23-10 Control of RespirationRespiratory Centers of the Medulla OblongataSet the pace of respirationCan be divided into two groups Dorsal respiratory group (DRG) Ventral respiratory group (VRG)23-10 Control of RespirationDorsal Respiratory Group (DRG) Inspiratory centerFunctions in quiet and forced breathingVentral Respiratory Group (VRG)Inspiratory and expiratory centerFunctions only in forced breathing23-10 Control of RespirationQuiet Breathing Brief activity in the DRGStimulates inspiratory musclesDRG neurons become inactiveAllowing passive exhalation23-10 Control of RespirationForced Breathing Increased activity in DRGStimulates VRGWhich activates accessory inspiratory musclesAfter inhalationExpiratory center neurons stimulate active exhalation23-10 Control of RespirationThe Apneustic and Pneumotaxic Centers of the Pons Paired nuclei that adjust output of respiratory rhythmicity centersRegulating respiratory rate and depth of respirationApneustic CenterProvides continuous stimulation to its DRG centerPneumotaxic Centers Inhibit the apneustic centersPromote passive or active exhalation23-10 Control of RespirationRespiratory Centers and Reflex Controls Interactions between VRG and DRGEstablish basic pace and depth of respirationThe pneumotaxic centerModifies the pace23-10 Control of RespirationSudden Infant Death Syndrome (SIDS) Disrupts normal respiratory reflex patternMay result from connection problems between pacemaker complex and respiratory centers23-10 Control of RespirationRespiratory Reflexes Chemoreceptors are sensitive to PCO2, PO2, or pH of blood or cerebrospinal fluidBaroreceptors in aortic or carotid sinuses are sensitive to changes in blood pressureStretch receptors respond to changes in lung volume Irritating physical or chemical stimuli in nasal cavity, larynx, or bronchial treeOther sensations including pain, changes in body temperature, abnormal visceral sensations23-10 Control of RespirationThe Chemoreceptor Reflexes Respiratory centers are strongly influenced by chemoreceptor input from:Glossopharyngeal nerve (N IX)Vagus nerve (N X)Central chemoreceptors that monitor cerebrospinal fluid23-10 Control of RespirationThe Chemoreceptor Reflexes The glossopharyngeal nerveFrom carotid bodiesStimulated by changes in blood pH or PO2 The vagus nerveFrom aortic bodiesStimulated by changes in blood pH or PO223-10 Control of RespirationThe Chemoreceptor Reflexes Central chemoreceptors that monitor cerebrospinal fluidAre on ventrolateral surface of medulla oblongataRespond to PCO2 and pH of CSF23-10 Control of RespirationChemoreceptor Stimulation Leads to increased depth and rate of respirationIs subject to adaptationDecreased sensitivity due to chronic stimulation23-10 Control of RespirationHypercapnia An increase in arterial PCO2 Stimulates chemoreceptors in the medulla oblongataTo restore homeostasis23-10 Control of RespirationHypercapnia and HypocapniaHypoventilation is a common cause of hypercapniaAbnormally low respiration rateAllows CO2 buildup in bloodExcessive ventilation, hyperventilation, results in abnormally low PCO2 (hypocapnia)Stimulates chemoreceptors to decrease respiratory rate23-10 Control of RespirationThe Baroreceptor Reflexes Carotid and aortic baroreceptor stimulationAffects blood pressure and respiratory centersWhen blood pressure falls:Respiration increasesWhen blood pressure increases:Respiration decreases23-10 Control of RespirationThe HeringBreuer Reflexes Two baroreceptor reflexes involved in forced breathing Inflation reflexPrevents overexpansion of lungs Deflation reflexInhibits expiratory centersStimulates inspiratory centers during lung deflation23-10 Control of RespirationProtective Reflexes Triggered by receptors in epithelium of respiratory tract when lungs are exposed to:Toxic vaporsChemical irritantsMechanical stimulationCause sneezing, coughing, and laryngeal spasm23-10 Control of RespirationApnea A period of suspended respirationNormally followed by explosive exhalation to clear airwaysSneezing and coughingLaryngeal Spasm Temporarily closes airwayTo prevent foreign substances from entering23-10 Control of RespirationVoluntary Control of Respiration Strong emotions can stimulate respiratory centers in hypothalamusEmotional stress can activate sympathetic or parasympathetic division of ANSCausing bronchodilation or bronchoconstriction Anticipation of strenuous exercise can increase respiratory rate and cardiac output by sympathetic stimulation23-10 Control of RespirationChanges in the Respiratory System at BirthBefore birthPulmonary vessels are collapsedLungs contain no airDuring deliveryPlacental connection is lostBlood PO2 fallsPCO2 rises23-10 Control of RespirationChanges in the Respiratory System at Birth At birthNewborn overcomes force of surface tension to inflate bronchial tree and alveoli and take first breathLarge drop in pressure at first breathPulls blood into pulmonary circulationClosing foramen ovale and ductus arteriosusRedirecting fetal blood circulation patterns Subsequent breaths fully inflate alveoli23-11 Effects of Aging on the Respiratory SystemThree Effects of Aging on the Respiratory SystemElastic tissues deteriorateAltering lung compliance and lowering vital capacityArthritic changesRestrict chest movementsLimit respiratory minute volumeEmphysemaAffects individuals over age 50Depending on exposure to respiratory irritants (e.g., cigarette smoke)23-12 Respiratory System IntegrationRespiratory ActivityMaintaining homeostatic O2 and CO2 levels in peripheral tissues requires coordination between several systems Particularly the respiratory and cardiovascular systems23-12 Respiratory System IntegrationCoordination of Respiratory and Cardiovascular Systems Improves efficiency of gas exchange by controlling lung perfusionIncreases respiratory drive through chemoreceptor stimulationRaises cardiac output and blood flow through baroreceptor stimulation ................
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