Y khoa, y dược - The respiratory system: Part A

22 The Respiratory System:Part ARespirationInvolves both the respiratory and the circulatory systemsFour processes that supply the body with O2 and dispose of CO2RespirationPulmonary ventilation (breathing):movement of air into and outof the lungsExternal respiration: O2 and CO2exchange between the lungsand the bloodTransport: O2 and CO2in the bloodInternal respiration: O2 and CO2exchange between systemic bloodvessels and tissuesRespiratorysystemCirculatorysystemRespiratory System: Functional AnatomyMajor organsNose, nasal cavity, and paranasal sinusesPharynxLarynxTracheaBronchi and their branchesLungs and alveoliFigure 22.1Nasal cavityNostrilOral cavityPharynxLarynxTracheaCarina of tracheaLeft main(primary) bronchusRight main (primary) bronchusRight lungLeft lungDiaphragmFunctional AnatomyRespiratory zone: site of gas exchange Microscopic structures: respiratory bronchioles, alveolar ducts, and alveoliConducting zone: conduits to gas exchange sitesIncludes all other respiratory structuresRespiratory muscles: diaphragm and other muscles that promote ventilationPLAYAnimation: Rotatable faceThe NoseFunctionsProvides an airway for respirationMoistens and warms the entering airFilters and cleans inspired air Serves as a resonating chamber for speechHouses olfactory receptorsThe NoseTwo regions: external nose and nasal cavityExternal nose: root, bridge, dorsum nasi, and apex Philtrum: a shallow vertical groove inferior to the apexNostrils (nares): bounded laterally by the alaeFigure 22.2aEpicranius,frontal bellyAla of noseRoot and bridge of noseDorsum nasiApex of nosePhiltrumNaris (nostril)(a) Surface anatomyFigure 22.2bFrontal boneNasal boneSeptal cartilageMaxillary bone(frontal process)Lateral process ofseptal cartilageMinor alar cartilagesMajor alarcartilagesDense fibrousconnective tissue(b) External skeletal frameworkThe NoseNasal cavity: in and posterior to the external noseDivided by a midline nasal septumPosterior nasal apertures (choanae) open into the nasal pharynx Roof: ethmoid and sphenoid bones Floor: hard and soft palatesNasal CavityVestibule: nasal cavity superior to the nostrils Vibrissae filter coarse particles from inspired airOlfactory mucosaLines the superior nasal cavity Contains smell receptorsNasal CavityRespiratory mucosaPseudostratified ciliated columnar epitheliumMucous and serous secretions contain lysozyme and defensins Cilia move contaminated mucus posteriorly to throatInspired air is warmed by plexuses of capillaries and veinsSensory nerve endings triggers sneezingFigure 22.3cSphenoid sinusFrontal sinusNasal meatuses(superior, middle,and inferior)NasopharynxUvulaPalatine tonsilIsthmus of thefaucesPosterior nasalapertureOpening ofpharyngotympanictubePharyngeal tonsilOropharynxLaryngopharynxVocal foldEsophagus(c) IllustrationNasal conchae(superior, middle and inferior)Nasal vestibuleNostrilNasal cavityHard palateSoft palateTongueLingual tonsilEpiglottisHyoid boneLarynxThyroid cartilageVestibular foldCricoid cartilageThyroid glandTracheaCribriform plateof ethmoid boneNasal CavitySuperior, middle, and inferior nasal conchaeProtrude from the lateral wallsIncrease mucosal areaEnhance air turbulence Functions of the Nasal Mucosa and ConchaeDuring inhalation, the conchae and nasal mucosaFilter, heat, and moisten airDuring exhalation these structuresReclaim heat and moistureParanasal SinusesIn frontal, sphenoid, ethmoid, and maxillary bonesLighten the skull and help to warm and moisten the airPharynxMuscular tube that connects to theNasal cavity and mouth superiorlyLarynx and esophagus inferiorlyFrom the base of the skull to the level of the sixth cervical vertebraFigure 22.3bPharynxNasopharynxOropharynxLaryngopharynx(b) Regions of the pharynxNasopharynxAir passageway posterior to the nasal cavityLining: pseudostratified columnar epitheliumSoft palate and uvula close nasopharynx during swallowingPharyngeal tonsil (adenoids) on posterior wall Pharyngotympanic (auditory) tubes open into the lateral wallsOropharynxPassageway for food and air from the level of the soft palate to the epiglottisLining of stratified squamous epithelium Isthmus of the fauces: opening to the oral cavity Palatine tonsils in the lateral walls of faucesLingual tonsil on the posterior surface of the tongueLaryngopharynxPassageway for food and airPosterior to the upright epiglottisExtends to the larynx, where it is also continuous with the esophagusFigure 22.3cSphenoid sinusFrontal sinusNasal meatuses(superior, middle,and inferior)NasopharynxUvulaPalatine tonsilIsthmus of thefaucesPosterior nasalapertureOpening ofpharyngotympanictubePharyngeal tonsilOropharynxLaryngopharynxVocal foldEsophagus(c) IllustrationNasal conchae(superior, middle and inferior)Nasal vestibuleNostrilNasal cavityHard palateSoft palateTongueLingual tonsilEpiglottisHyoid boneLarynxThyroid cartilageVestibular foldCricoid cartilageThyroid glandTracheaCribriform plateof ethmoid boneLarynx Attaches to the hyoid bone and opens into the laryngopharynx Continuous with the tracheaFunctionsProvides a patent airwayRoutes air and food into proper channelsVoice productionLarynxCartilages of the larynxHyaline cartilage except for the epiglottisThyroid cartilage with laryngeal prominence (Adam’s apple)Ring-shaped cricoid cartilagePaired arytenoid, cuneiform, and corniculate cartilagesEpiglottis: elastic cartilage; covers the laryngeal inlet during swallowingFigure 22.4aBody of hyoid boneEpiglottisCricoid cartilageTracheal cartilagesThyroid cartilageLaryngeal prominence(Adam’s apple)Cricothyroid ligamentCricotracheal ligament(a) Anterior superficial viewThyrohyoidmembraneFigure 22.4bEpiglottisBody of hyoid boneThyrohyoid membraneVestibular fold(false vocal cord)Vocal fold(true vocal cord)Cricothyroid ligamentCricotracheal ligamentFatty padThyroid cartilageCuneiform cartilageCorniculate cartilageArytenoid cartilageCricoid cartilageTracheal cartilagesArytenoid muscles(b) Sagittal view; anterior surface to the rightThyrohyoidmembraneLarynxVocal ligamentsAttach the arytenoid cartilages to the thyroid cartilageContain elastic fibers Form core of vocal folds (true vocal cords)Opening between them is the glottisFolds vibrate to produce sound as air rushes up from the lungsLarynxVestibular folds (false vocal cords)Superior to the vocal foldsNo part in sound productionHelp to close the glottis during swallowingFigure 22.5(a) Vocal folds in closed position; closed glottis (b) Vocal folds in open position; open glottis Base of tongueEpiglottisVestibular fold(false vocal cord) Vocal fold(true vocal cord) GlottisInner lining of tracheaCuneiform cartilageCorniculate cartilageVoice ProductionSpeech: intermittent release of expired air while opening and closing the glottisPitch is determined by the length and tension of the vocal cords Loudness depends upon the force of airChambers of pharynx, oral, nasal, and sinus cavities amplify and enhance sound quality Sound is “shaped” into language by muscles of the pharynx, tongue, soft palate, and lips LarynxVocal folds may act as a sphincter to prevent air passageExample: Valsalva’s maneuverGlottis closes to prevent exhalationAbdominal muscles contractIntra-abdominal pressure rises Helps to empty the rectum or stabilizes the trunk during heavy liftingTracheaWindpipe: from the larynx into the mediastinum Wall composed of three layersMucosa: ciliated pseudostratified epithelium with goblet cells Submucosa: connective tissue with seromucous glandsAdventitia: outermost layer made of connective tissue that encases the C-shaped rings of hyaline cartilageTracheaTrachealis muscleConnects posterior parts of cartilage ringsContracts during coughing to expel mucusCarinaLast tracheal cartilagePoint where trachea branches into two bronchiFigure 22.6a(a) Cross section of the trachea and esophagusHyaline cartilageSubmucosaMucosaSeromucous glandin submucosaPosteriorLumen of tracheaAnteriorEsophagusTrachealismuscleAdventitiaFigure 22.6b(b) Photomicrograph of the tracheal wall (320x)Hyaline cartilage• Lamina propria (connective tissue)SubmucosaMucosaSeromucous glandin submucosa• Pseudostratified ciliated columnar epitheliumBronchi and SubdivisionsAir passages undergo 23 orders of branching Branching pattern called the bronchial (respiratory) treeConducting Zone StructuresTrachea  right and left main (primary) bronchiEach main bronchus enters the hilum of one lungRight main bronchus is wider, shorter, and more vertical than the leftEach main bronchus branches into lobar (secondary) bronchi (three right, two left)Each lobar bronchus supplies one lobe Conducting Zone StructuresEach lobar bronchus branches into segmental (tertiary) bronchiSegmental bronchi divide repeatedlyBronchioles are less than 1 mm in diameterTerminal bronchioles are the smallest, less than 0.5 mm diameterFigure 22.7TracheaSuperior lobe of right lungMiddle lobe of right lungInferior lobe of right lungSuperior lobe of left lungLeft main(primary) bronchusLobar (secondary)bronchusSegmental (tertiary)bronchusInferior lobeof left lungConducting Zone StructuresFrom bronchi through bronchioles, structural changes occurCartilage rings give way to plates; cartilage is absent from bronchiolesEpithelium changes from pseudostratified columnar to cuboidal; cilia and goblet cells become sparseRelative amount of smooth muscle increasesRespiratory ZoneRespiratory bronchioles, alveolar ducts, alveolar sacs (clusters of alveoli)~300 million alveoli account for most of the lungs’ volume and are the main site for gas exchangeFigure 22.8a(a)Alveolar ductAlveolar ductAlveoliAlveolarsacRespiratory bronchiolesTerminalbronchioleFigure 22.8b(b)AlveolarporesAlveolarductRespiratorybronchioleAlveoliAlveolarsacRespiratory Membrane~0.5-m-thick air-blood barrierAlveolar and capillary walls and their fused basement membranesAlveolar wallsSingle layer of squamous epithelium (type I cells)Scattered type II cuboidal cells secrete surfactant and antimicrobial proteinsFigure 22.9aElasticfibers(a) Diagrammatic view of capillary-alveoli relationshipsSmoothmuscleAlveolusCapillariesTerminal bronchioleRespiratory bronchioleFigure 22.9bAlveoliSurrounded by fine elastic fibersContain open pores thatConnect adjacent alveoliAllow air pressure throughout the lung to be equalizedHouse alveolar macrophages that keep alveolar surfaces sterileFigure 22.9cCapillaryType II (surfactant-secreting) cellType I cellof alveolar wall Endothelial cell nucleusMacrophageAlveoli (gas-filledair spaces)Red blood cellin capillaryAlveolar poresCapillary endotheliumFused basement membranes of the alveolar epitheliumand the capillary endotheliumAlveolar epitheliumRespiratorymembraneRed blood cellO2AlveolusCO2CapillaryAlveolusNucleus of type I(squamousepithelial) cell(c) Detailed anatomy of the respiratory membrane Lungs Occupy all of the thoracic cavity except the mediastinumRoot: site of vascular and bronchial attachmentsCostal surface: anterior, lateral, and posterior surfaces Figure 22.10cEsophagus(in mediastinum)Right lungParietal pleuraVisceralpleura Pleural cavityPericardial membranesSternumAnteriorPosteriorRoot of lungat hilumLeft lungThoracic wallPulmonary trunkHeart (in mediastinum)Anterior mediastinum(c) Transverse section through the thorax, viewed from above. Lungs, pleural membranes, and major organs in the mediastinum are shown.• Left main bronchus• Left pulmonary artery• Left pulmonary veinVertebraLungsApex: superior tipBase: inferior surface that rests on the diaphragmHilum: on mediastinal surface; site for attachment of blood vessels, bronchi, lymphatic vessels, and nerves Cardiac notch of left lung: concavity that accommodates the heartLungsLeft lung is smaller, separated into two lobes by an oblique fissureRight lung has three lobes separated by oblique and horizontal fissuresBronchopulmonary segments (10 right, 8–9 left)Lobules are the smallest subdivisions; served by bronchioles and their branchesFigure 22.10aTracheaApex of lungThymusRight superior lobeHorizontal fissureRight middle lobeOblique fissureRight inferior lobeHeart(in mediastinum)DiaphragmBase of lungLeftsuperior lobeCardiac notchObliquefissureLeft inferiorlobeLungPleural cavityParietal pleuraRibIntercostal muscleVisceral pleura(a) Anterior view. The lungs flank mediastinal structures laterally.Figure 22.11Rightsuperiorlobe (3segments)Rightmiddlelobe (2segments)Rightinferior lobe (5 segments)Left superiorlobe(4 segments)Left inferiorlobe (5 segments)Right lungLeft lungBlood Supply Pulmonary circulation (low pressure, high volume)Pulmonary arteries deliver systemic venous blood Branch profusely, along with bronchiFeed into the pulmonary capillary networksPulmonary veins carry oxygenated blood from respiratory zones to the heartBlood Supply Systemic circulation (high pressure, low volume)Bronchial arteries provide oxygenated blood to lung tissueArise from aorta and enter the lungs at the hilumSupply all lung tissue except the alveoliBronchial veins anastomose with pulmonary veinsPulmonary veins carry most venous blood back to the heartPleuraeThin, double-layered serosa Parietal pleura on thoracic wall and superior face of diaphragmVisceral pleura on external lung surfacePleural fluid fills the slitlike pleural cavityProvides lubrication and surface tensionFigure 22.10cEsophagus(in mediastinum)Right lungParietal pleuraVisceralpleura Pleural cavityPericardial membranesSternumAnteriorPosteriorRoot of lungat hilumLeft lungThoracic wallPulmonary trunkHeart (in mediastinum)Anterior mediastinum(c) Transverse section through the thorax, viewed from above. Lungs, pleural membranes, and major organs in the mediastinum are shown.• Left main bronchus• Left pulmonary artery• Left pulmonary veinVertebraMechanics of BreathingPulmonary ventilation consists of two phasesInspiration: gases flow into the lungsExpiration: gases exit the lungsPressure Relationships in the Thoracic CavityAtmospheric pressure (Patm)Pressure exerted by the air surrounding the body 760 mm Hg at sea levelRespiratory pressures are described relative to PatmNegative respiratory pressure is less than Patm Positive respiratory pressure is greater than PatmZero respiratory pressure = PatmIntrapulmonary PressureIntrapulmonary (intra-alveolar) pressure (Ppul)Pressure in the alveoliFluctuates with breathingAlways eventually equalizes with PatmIntrapleural PressureIntrapleural pressure (Pip):Pressure in the pleural cavityFluctuates with breathingAlways a negative pressure (<Patm and <Ppul)Intrapleural PressureNegative Pip is caused by opposing forcesTwo inward forces promote lung collapseElastic recoil of lungs decreases lung sizeSurface tension of alveolar fluid reduces alveolar sizeOne outward force tends to enlarge the lungsElasticity of the chest wall pulls the thorax outwardPressure RelationshipsIf Pip = Ppul the lungs collapse(Ppul – Pip) = transpulmonary pressureKeeps the airways openThe greater the transpulmonary pressure, the larger the lungsFigure 22.12Atmospheric pressureIntrapleuralpressure756 mm Hg(–4 mm Hg)Transpulmonarypressure760 mm Hg –756 mm Hg= 4 mm HgThoracic wallDiaphragmLungIntrapulmonarypressure 760 mm Hg(0 mm Hg)Parietal pleuraPleural cavityVisceral pleura756760Homeostatic ImbalanceAtelectasis (lung collapse) is due toPlugged bronchioles  collapse of alveoliWound that admits air into pleural cavity (pneumothorax)Pulmonary VentilationInspiration and expirationMechanical processes that depend on volume changes in the thoracic cavityVolume changes  pressure changesPressure changes  gases flow to equalize pressureBoyle’s LawThe relationship between the pressure and volume of a gasPressure (P) varies inversely with volume (V): P1V1 = P2V2InspirationAn active processInspiratory muscles contract Thoracic volume increasesLungs are stretched and intrapulmonary volume increasesIntrapulmonary pressure drops (to 1 mm Hg)Air flows into the lungs, down its pressure gradient, until Ppul = PatmFigure 22.13 (1 of 2)Sequence of eventsChanges in anterior-posterior and superior-inferior dimensionsChanges in lateraldimensions(superior view)Ribs are elevatedand sternum flaresas externalintercostalscontract.Diaphragmmoves inferiorlyduring contraction.Externalintercostalscontract. Inspiratory muscles contract (diaphragm descends; rib cage rises).21 Thoracic cavity volume increases.3 Lungs are stretched; intrapulmonary volume increases.4 Intrapulmonary pressure drops (to –1 mm Hg).5 Air (gases) flows into lungs down its pressure gradient until intrapulmonary pressure is 0 (equal to atmospheric pressure).ExpirationQuiet expiration is normally a passive processInspiratory muscles relax Thoracic cavity volume decreasesElastic lungs recoil and intrapulmonary volume decreasesPpul rises (to +1 mm Hg)Air flows out of the lungs down its pressure gradient until Ppul = 0Note: forced expiration is an active process: it uses abdominal and internal intercostal musclesFigure 22.13 (2 of 2)Sequenceof eventsChanges in anterior-posterior and superior-inferior dimensionsChanges inlateral dimensions(superior view)Ribs and sternumare depressedas externalintercostalsrelax.Externalintercostalsrelax.Diaphragmmovessuperiorlyas it relaxes.1 Inspiratory muscles relax (diaphragm rises; rib cage descends due to recoil of costal cartilages).2 Thoracic cavity volume decreases.3 Elastic lungs recoil passively; intrapulmonary volume decreases.4 Intrapulmonary pres-sure rises (to +1 mm Hg).5 Air (gases) flows out of lungs down its pressure gradient until intra-pulmonary pressure is 0.Figure 22.145 seconds elapsedVolume of breathIntrapulmonarypressureExpirationIntrapleuralpressureTrans-pulmonarypressureInspirationIntrapulmonary pressure. Pressure inside lung decreases as lung volume increases during inspiration; pressure increases during expiration.Intrapleural pressure.Pleural cavity pressure becomes more negative as chest wall expands during inspiration. Returns to initial value as chest wall recoils. Volume of breath.During each breath, the pressure gradients move 0.5 liter of air into and out of the lungs.Physical Factors Influencing Pulmonary VentilationInspiratory muscles consume energy to overcome three factors that hinder air passage and pulmonary ventilationAirway resistanceAlveolar surface tensionLung complianceAirway ResistanceFriction is the major nonelastic source of resistance to gas flowThe relationship between flow (F), pressure (P), and resistance (R) is: F = P RP is the pressure gradient between the atmosphere and the alveoli (2 mm Hg or less during normal quiet breathing)Gas flow changes inversely with resistanceAirway ResistanceResistance is usually insignificant because ofLarge airway diameters in the first part of the conducting zoneProgressive branching of airways as they get smaller, increasing the total cross-sectional areaResistance disappears at the terminal bronchioles where diffusion drives gas movement Figure 22.15Airway generation(stage of branching)Medium-sizedbronchiTerminalbronchiolesConductingzoneRespiratoryzoneAirway ResistanceAs airway resistance rises, breathing movements become more strenuousSeverely constricting or obstruction of bronchiolesCan prevent life-sustaining ventilationCan occur during acute asthma attacks and stop ventilationEpinephrine dilates bronchioles and reduces air resistanceAlveolar Surface TensionSurface tensionAttracts liquid molecules to one another at a gas-liquid interface Resists any force that tends to increase the surface area of the liquidAlveolar Surface TensionSurfactantDetergent-like lipid and protein complex produced by type II alveolar cellsReduces surface tension of alveolar fluid and discourages alveolar collapseInsufficient quantity in premature infants causes infant respiratory distress syndromeLung ComplianceA measure of the change in lung volume that occurs with a given change in transpulmonary pressureNormally high due toDistensibility of the lung tissue Alveolar surface tensionLung ComplianceDiminished byNonelastic scar tissue (fibrosis) Reduced production of surfactantDecreased flexibility of the thoracic cageLung ComplianceHomeostatic imbalances that reduce compliance Deformities of thoraxOssification of the costal cartilageParalysis of intercostal muscles