Chapter 23: The Respiratory System

The Respiratory System

The Respiratory SystemCells produce energy:for maintenance, growth, defense, and divisionthrough mechanisms that use oxygen and produce carbon dioxideOxygenIs 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 5 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 senseComponents of the Respiratory SystemOrganization of the Respiratory SystemThe respiratory system is divided into the upper respiratory system, above the larynx, and the lower respiratory system, from the larynx down

The Respiratory TractConsists of a conducting portion:from nasal cavity to terminal bronchiolesConsists of a respiratory portion:the respiratory bronchioles and alveoli AlveoliAre air-filled pockets within the lungswhere all gas exchange takes place

The Respiratory EpitheliumThe Respiratory EpitheliumFigure 232

The Respiratory EpitheliumFor 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)The Respiratory MucosaConsists of:an epithelial layeran areolar layerLines conducting portion of respiratory system The Lamina PropriaUnderlies areolar tissueIn the upper respiratory system, trachea, and bronchi:contains mucous glands that secrete onto epithelial surfaceIn the conducting portion of lower respiratory system:contains smooth muscle cells that encircle lumen of bronchiolesStructure of Respiratory EpitheliumChanges along respiratory tractAlveolar EpitheliumIs a very delicate, simple squamous epitheliumContains scattered and specialized cellsLines exchange surfaces of alveoli

How are delicate respiratory exchange surfaces protected from pathogens, debris, and other hazards?The Respiratory Defense System Consists of a series of filtration mechanismsRemoves particles and pathogens * Components of the Respiratory Defense SystemGoblet cells and mucous glands: produce mucus that bathes exposed surfacesCilia: sweep debris trapped in mucus toward the pharynx (mucus escalator)Filtration in nasal cavity removes large particlesAlveolar macrophages engulf small particles that reach lungsThe Upper Respiratory SystemFigure 233

The Nose Air enters the respiratory system:through nostrils or external naresinto nasal vestibule Nasal hairs:are in nasal vestibule are the first particle filtration systemThe Nasal CavityThe nasal septum:divides nasal cavity into left and rightMucous secretions from paranasal sinus and tears:clean and moisten the nasal cavitySuperior portion of nasal cavity is the olfactory region:provides sense of smellAir FlowFrom vestibule to internal nares:through superior, middle, and inferior meatusesMeatusesConstricted passageways that produce air turbulence:warm and humidify incoming airtrap particles

The PalatesHard palate:forms floor of nasal cavityseparates nasal and oral cavitiesSoft palate:extends posterior to hard palatedivides superior nasopharynx from lower pharynxAir FlowNasal cavity opens into nasopharynx through internal naresThe Nasal MucosaWarm and humidify inhaled air for arrival at lower respiratory organs Breathing through mouth bypasses this important step

The Pharynx and DivisionsA chamber shared by digestive and respiratory systemsExtends from internal nares to entrances to larynx and esophagusNasopharynxOropharynxLaryngopharynx

The Nasopharynx Superior portion of the pharynxContains pharyngeal tonsils and openings to left and right auditory tubesThe OropharynxMiddle portion of the pharynxCommunicates with oral cavityThe LaryngopharynxInferior portion of the pharynxExtends from hyoid bone to entrance to larynx and esophagusWhat is the structure of the larynx and its role in normal breathing and production of sound?Anatomy of the LarynxFigure 234

Air Flow-From the pharynx enters the larynx:a cartilaginous structure that surrounds the glottisCartilages of the Larynx3 large, unpaired cartilages form the larynx:the thyroid cartilage the cricoid cartilagethe epiglottis

The Thyroid Cartilage Also called the Adams appleIs a hyaline cartilageForms anterior and lateral walls of larynxLigaments attach to hyoid bone, epiglottis, and laryngeal cartilages

The Cricoid CartilageIs a hyaline cartilageForm posterior portion of larynxLigaments attach to first tracheal cartilageArticulates with arytenoid cartilagesThe EpiglottisComposed of elastic cartilageLigaments attach to thyroid cartilage and hyoid bone

Cartilage FunctionsThyroid 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 tractThe GlottisFigure 235

3 pairs of Small Hyaline Cartilages of the Larynxarytenoid cartilages, corniculate cartilagescuneiform cartilagesCartilage FunctionsCorniculate and arytenoid cartilages function in:opening and closing of glottisproduction of sound

Ligaments of the LarynxVestibular ligaments and vocal ligaments:extend between thyroid cartilage and arytenoid cartilagesare covered by folds of laryngeal epithelium that project into glottis1) The Vestibular LigamentsLie within vestibular folds:which protect delicate vocal folds

Sound ProductionAir passing through glottis:vibrates vocal foldsproduces sound waves Sound VariationSound is varied by:tension on vocal folds: slender and short =high pitched, thicker and longer = low pitchedvoluntary muscles (position arytenoid cartilage relative to thyroid cartilage)

SpeechIs produced by:phonation:sound production at the larynxarticulation:modification of sound by other structuresThe Laryngeal MusculatureThe larynx is associated with:muscles of neck and pharynxintrinsic muscles that:control vocal foldsopen and close glottisCoughing reflex: food or liquids went down the wrong pipe

Anatomy of the TracheaFigure 236

What is the structure of airways outside the lungs?The Trachea Also called the windpipeExtends from the cricoid cartilage into mediastinumwhere it branches into right and left pulmonary bronchiThe SubmucosaBeneath mucosa of trachea Contains mucous glands

The Tracheal Cartilages 1520 tracheal cartilages:strengthen and protect airwaydiscontinuous where trachea contacts esophagusEnds of each tracheal cartilage are connected by:an elastic ligament and trachealis muscle

The Primary BronchiRight and left primary bronchi:separated by an internal ridge (the carina)1) The Right Primary BronchusIs larger in diameter than the leftDescends at a steeper angle

Structure of Primary BronchiEach primary bronchus:travels to a groove (hilus) along medial surface of the lung Hilus-Where pulmonary nerves, blood vessels, and lymphatics enter lungAnchored in meshwork of connective tissue

The Root of the LungComplex of connective tissues, nerves, and vessels in hilus:anchored to the mediastinum Figure 237Gross Anatomy of the Lungs

Left and right lungs:are in left and right pleural cavitiesThe base:inferior portion of each lung rests on superior surface of diaphragmLobes of the LungsLungs have lobes separated by deep fissures 1) The Right Lung- Has 3 lobes: superior, middle, and inferiorseparated by horizontal and oblique fissures2) The Left Lung- Has 2 lobes: superior and inferiorare separated by an oblique fissureRelationship between Lungs and HeartFigure 238

Lung ShapeRight lung:is wider is displaced upward by liverLeft lung:is longer is displaced leftward by the heart forming the cardiac notch

The Bronchial TreeIs formed by the primary bronchi and their branchesExtrapulmonary BronchiThe left and right bronchi branches outside the lungs Intrapulmonary BronchiBranches within the lungs

Bronchi and LobulesFigure 239

A Primary Bronchus

Branches to form secondary bronchi (lobar bronchi)1 secondary bronchus goes to each lobeSecondary Bronchi Branch to form tertiary bronchi, also called the segmental bronchiEach segmental bronchus:supplies air to a single bronchopulmonary segment-The right lung has 10The left lung has 8 or 9Bronchial StructureThe walls of primary, secondary, and tertiary bronchi:contain progressively less cartilage and more smooth muscleincreasing muscular effects on airway constriction and resistance Figure 2310The Bronchioles

Bronchitis: Inflammation of bronchial walls: causes constriction and breathing difficultyThe BronchiolesEach tertiary bronchus branches into multiple bronchiolesBronchioles branch into terminal bronchioles: 1 tertiary bronchus forms about 6500 terminal bronchiolesBronchiole StructureBronchioles:have no cartilageare dominated by smooth muscle Autonomic ControlRegulates smooth muscle:controls diameter of bronchiolescontrols airflow and resistance in lungsBronchodilationDilation of bronchial airwaysCaused by sympathetic ANS activation Reduces resistance BronchoconstrictionConstricts bronchiCaused by: parasympathetic ANS activationhistamine release (allergic reactions)AsthmaExcessive stimulation and bronchoconstriction Stimulation severely restricts airflowPulmonary LobulesAre the smallest compartments of the lungAre divided by the smallest trabecular partitions (interlobular septa)

Each terminal bronchiole delivers air to a single pulmonary lobuleEach pulmonary lobule is supplied by pulmonary arteries and veins

Exchange SurfacesWithin the lobule:each terminal bronchiole branches to form several respiratory bronchioles, where gas exchange takes placeAlveolar Organization

Respiratory bronchioles are connected to alveoli along alveolar ductsAlveolar ducts end at alveolar sacs: common chambers connected to many individual alveoli An AlveolusHas an extensive network of capillariesIs surrounded by elastic fibers Alveolar EpitheliumConsists of simple squamous epitheliumConsists of thin, delicate Type I cellsPatrolled by alveolar macrophages, also called dust cellsContains septal cells (Type II cells) that produce Surfactant- an oily secretion which 1) Contains phospholipids and proteins2) Coats alveolar surfaces and reduces surface tensionRespiratory DistressDifficult respiration:due to alveolar collapse caused when septal cells do not produce enough surfactant Respiratory Membrane - The thin membrane of alveoli where gas exchange takes place 3 Parts of the Respiratory Membrane Squamous epithelial lining of alveolusEndothelial cells lining an adjacent capillaryFused basal laminae between alveolar and endothelial cellsDiffusion- Across respiratory membrane is very rapid:because distance is small gases (O2 and CO2) are lipid solubleInflammation of Lobules Also called pneumonia:causes fluid to leak into alveolicompromises function of respiratory membraneBlood Supply to Respiratory SurfacesEach lobule receives an arteriole and a venulerespiratory exchange surfaces receive blood:from arteries of pulmonary circuita capillary network surrounds each alveolus:as part of the respiratory membraneblood from alveolar capillaries:passes through pulmonary venules and veinsreturns to left atrium Blood Supply to the Lungs Capillaries supplied by bronchial arteries:provide oxygen and nutrients to tissues of conducting passageways of lung Venous blood bypasses the systemic circuit and flows into pulmonary veinsBlood Pressure In pulmonary circuit is low (30 mm Hg)Pulmonary vessels are easily blocked by blood clots, fat, or air bubbles, causing pulmonary embolismFigure 238Pleural Cavities and Pleural Membranes

Pleural Cavities and Pleural Membranes2 pleural cavities:are separated by the mediastinumEach pleural cavity:holds a lung is lined with a serous membrane (the pleura)Pleura consist of 2 layers: parietal pleura visceral pleuraPleural fluid:lubricates space between 2 layersFigure 2316a, bThe Respiratory Muscles

Most important are:the diaphragm external intracostal muscles of the ribsaccessory respiratory muscles:activated when respiration increases significantlyThe Respiratory MusclesFigure 2316c, d

The Mechanics of BreathingInhalation:always activeExhalation:active or passive3 Muscle Groups of Inhalation Diaphragm:contraction draws air into lungs75% of normal air movementExternal intracostal muscles:assist inhalation25% of normal air movementAccessory muscles assist in elevating ribs:sternocleidomastoidserratus anteriorpectoralis minorscalene musclesMuscles of Active Exhalation Internal intercostal and transversus thoracis muscles:depress the ribsAbdominal muscles:compress the abdomenforce diaphragm upwardModes of BreathingRespiratory movements are classified:by pattern of muscle activityinto quiet breathing and forced breathingQuiet Breathing (Eupnea) Involves active inhalation and passive exhalationDiaphragmatic breathing or deep breathing:is dominated by diaphragm Costal breathing or shallow breathing:is dominated by ribcage movements Elastic ReboundWhen inhalation muscles relax:elastic components of muscles and lungs recoilreturning lungs and alveoli to original positionForced Breathing Also called hyperpnea Involves active inhalation and exhalationAssisted by accessory musclesMaximum levels occur in exhaustion