The Respiratory System Chapter 22
The Respiratory System Chapter 22 The Respiratory System • Principal function: – Gas transport – Gas exchange Nasal cavity • Supplies body with oxygen Nostril • Disposes of carbon dioxide Larynx • Participates in: – Regulating blood pH – Has receptors for smell – Filters inhaled air – Produces sounds – Rids body of small amount of water and heat in exhaled air Trachea Carina of trachea Right main (primary) bronchus Right lung Parietal pleura Oral cavity Pharynx Left main (primary) bronchus Bronchi Alveoli Left lung Diaphragm Functional Anatomy of Respiratory System • Upper Respiratory system: – Nose, nasal cavity, paranasal sinuses – Pharynx (throat) • Lower respiratory system: – Larynx (boice box) – Trachea (windpipe) – Bronchi and smaller branches – Lungs and alveoli Respiratory System – functionally consists of two zones • Conducting zone – Nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, terminal bronchioles – Function: filter, warm, moisten and conduct air to the lungs • Respiratory zone – Respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli – Function: gas exchange between air and blood The Nose and Nasal Cavity • The Nose: – – – – – Provides an airway for respiration Moistens and warms air Filters inhaled air Resonating chamber for speech Houses olfactory receptors • The Nasal Cavity – External nares—nostrils – Divided by nasal septum – Conchae subdivides each side of the nasal cavity • Particulate matter deflected to mucus-coated surfaces – Continuous with nasopharynx • Posterior nasal apertures—choanae The Nose • Size variation due to differences in nasal cartilages • Skin is thin—contains many sebaceous glands Frontal bone Epicranius, frontal belly Root and bridge of nose Dorsum nasi Ala of nose Apex of nose Naris (nostril) Philtrum (a) Surface anatomy Nasal bone Septal cartilage Maxillary bone (frontal process) Lateral process of septal cartilage Minor alar cartilages Dense fibrous connective tissue Major alar cartilages (b) External skeletal framework Figure 22.2 The Upper Respiratory Tract Cribriform plate of ethmoid bone Sphenoid sinus Posterior nasal aperture Nasopharynx Pharyngeal tonsil Opening of pharyngotympanic tube Uvula Oropharynx Palatine tonsil Isthmus of the fauces Laryngopharynx Esophagus Trachea Frontal sinus Nasal cavity Nasal conchae (superior, middle and inferior) Nasal meatuses (superior, middle, and inferior) Nasal vestibule Nostril Hard palate Soft palate Tongue Larynx Epiglottis Vestibular fold Thyroid cartilage Vocal fold Cricoid cartilage Thyroid gland Lingual tonsil Hyoid bone Figure 22.3c Nasal Cavity • Mucous membrane lines the nasal cavity and conchae: – Olfactory mucosa • Near roof of nasal cavity • Houses olfactory (smell) receptors – Respiratory mucosa • Lines nasal cavity • Epithelium is pseudostratified ciliated columnar – Goblet cells within epithelium – Underlying layer of lamina propria – Cilia move contaminated mucus posteriorly Paranasal sinuses • Nasal cavity divided by a septum: nasal septum formed by the septal nasal cartilage – Attaches to the vomer and perpendicular plate of the ethmoid bone • Paranasal sinuses: frontal, sphenoidal, maxillary, ethmoidal Copyright 2012, John Wiley & Sons, Inc. Pharynx • Funnel-shaped tube ~13 cm (5 in.): starts at internal nares – Ends at cricoid cartilage (most inferior of the larynx) – Muscles innervated by cranial nerves IX and X • Functions of the pharynx – Passageway for air and food – Provides a resonating chamber for speech sounds – Houses the tonsils • The pharynx can be divided into three anatomical regions – Nasopharynx: respiratory pathway; pharyngeal tonsil (adenoid) – Oropharynx: both a respiratory and a digestive pathway • Fauces (throat); palatine and lingual tonsils – Laryngopharynx: both a respiratory and a digestive pathway Nose and Pharynx Larynx (Voice Box) • Connects the laryngopharynx with the trachea • The wall of the larynx is composed of nine cartilage – Three occur singly (thyroid cartilage, epiglottis, and cricoid cartilage) – Three occur in pairs (arytenoid, cuneiform, and corniculate cartilages) • The arytenoid cartilages are the true vocal cords The Larynx Body of hyoid bone • Three functions – Voice production – Provides an open airway – Routes air and food into the proper channels • Superior opening closed during swallowing and open during breathing Laryngeal prominence (Adam’s apple) Cricoid cartilage Sternal head Clavicular head Sternocleidomastoid Clavicle Jugular notch (a) Surface view Epiglottis Body of hyoid bone Thyrohyoid membrane Thyroid cartilage Laryngeal prominence (Adam’s apple) Cricothyroid ligament Cricoid cartilage Cricotracheal ligament Tracheal cartilages Figure 22.5a, b The Structures of Voice Production • Membrane of the larynx forms two pair of folds – Ventricular folds (superior pair): false vocal cords – Vocal folds (inferior pair): true vocal cords • Air passing through the larynx vibrates the folds and produces sound • Variation in pitch related to the tension in the vocal folds Movements of the Vocal Folds Anterior Thyroid cartilage Cricoid cartilage Vocal ligaments of vocal cords Glottis Lateral cricoarytenoid muscle Arytenoid cartilage Corniculate cartilage Posterior cricoarytenoid muscle Posterior Base of tongue Epiglottis Vestibular fold (false vocal cord) Vocal fold (true vocal cord) Glottis Inner lining of trachea Cuneiform cartilage Corniculate cartilage (a) Vocal folds in closed position; closed glottis (b) Vocal folds in open position; open glottis Figure 22.6 Anatomy of the Larynx Epiglottis Thyrohyoid membrane Hyoid bone • Sphincter function of the larynx – Valsalva’s maneuver: straining • Innervation of the larynx Corniculate cartilage Arytenoid cartilage Thyroid cartilage Cricoid cartilage Glottis – Recurrent laryngeal nerves (branch of vagus) Tracheal cartilages c) Cartilaginous framework of the larynx, posterior view Epiglottis Thyrohyoid membrane Cuneiform cartilage Corniculate cartilage Arytenoid cartilage Arytenoid muscle Cricoid cartilage Body of hyoid bone Thyrohyoid membrane Fatty pad Vestibular fold (false vocal cord) Thyroid cartilage Vocal fold (true vocal cord) Cricothyroid ligament Cricotracheal ligament Tracheal cartilages (d) Sagittal section (anterior on the right) Figure 22.5c, d The Trachea • Descends into the mediastinum – Smooth muscle and glands of trachea innervated by CN X • C-shaped cartilage rings keep airway open • Carina marks where trachea divides into two primary bronchi – Epithelium: pseudostratified ciliated columnar Posterior Mucosa Esophagus Trachealis muscle Lumen of trachea Submucosa Seromucous gland in submucosa Hyaline cartilage Adventitia Anterior (a) Cross section of the trachea and esophagus Bronchi in the Conducting Zone Superior lobe of right lung Trachea Superior lobe- left lung Left main (primary) bronchus Lobar (secondary) bronchus Segmental (tertiary) bronchus Inferior lobe -left lung Middle lobe Inferior lobe of right lung of right lung (a) The branching of the bronchial tree Figure 22.8a The Bronchial Tree • Divides into right and left primary bronchi at the carina • Bronchi divide to form secondary (lobar) bronchi, one for each lobe of the lung – Right lung: three lobes (3 lobar bronchi) – Left lung: two lobes (2 lobar bronchi) • Lobar branches into tertiary (segmental) bronchi – Segmental divides into bronchioles that branch repeatedly – Smallest bronchioles branch into the terminal bronchioles (contain Clara cells) Copyright 2012, John Wiley & Sons, Inc. The Bronchial Tree Copyright 2012, John Wiley & Sons, Inc. Changes in Tissue Composition Along Conducting Pathways • Supportive connective tissues change – C-shaped rings replaced by cartilage plates • Epithelium changes – First, pseudostratified ciliated columnar – Replaced by simple columnar, then simple cuboidal epithelium • Smooth muscle becomes important – Airways widen with sympathetic stimulation – Airways constrict under parasympathetic direction Structures of the Respiratory Zone • Consists of air-exchanging structures • Respiratory bronchioles—branch from terminal bronchioles – Lead to alveolar ducts that lead to alveolar sacs Alveoli Alveolar duct Respiratory bronchioles Terminal bronchiole Alveolar duct Alveolar sac (a) Figure 22.9a Structures of the Respiratory Zone Respiratory bronchiole Alveolar pores Alveolar duct Alveoli Alveolar sac (b) Figure 22.9b Structures of the Respiratory Zone • Alveoli - ~300 million alveoli account for tremendous surface area of the lungs – Surface area of alveoli is ˜140 square meters • Structure of alveoli – Type I cells: single layer of simple squamous epithelial cells • Surrounded by basal lamina • Alveolar and capillary walls plus basal lamina form respiratory membrane – Type II cells—scattered among type I cells • Cuboidal epithelial cells that secrete surfactant – Reduces surface tension within alveoli – Alveolar macrophages Features of Alveoli • Surrounded by elastic fibers • Interconnect by way of alveolar pores • Internal surfaces – site for free movement of alveolar macrophages Terminal bronchiole Respiratory bronchiole Smooth muscle Elastic fibers Alveolus Capillaries (a) Diagrammatic view of capillary-alveoli relationships Figure 22.10a, b Anatomy of Alveoli and the Respiratory Membrane Red blood cell Nucleus of type I (squamous epithelial) cell Alveolar pores Capillary O2 Macrophage Endothelial cell nucleus Alveolus Respiratory membrane Red blood cell Type I cell in capillary of alveolar wall Alveoli (gas-filled Type II (surfactantair spaces) secreting) cell (c) Detailed anatomy of the respiratory membrane Capillary CO2 Alveolus Alveolar epithelium Fused basement membranes of the alveolar epithelium and the capillary endothelium Capillary endothelium Figure 22.10c Gross Anatomy of the Lungs • Major landmarks – apex, base, hilum, and root • Left lung – superior and inferior lobes; oblique fissure • Right lung – superior, middle, and inferior lobes; horizontal and oblique fissures Intercostal muscle Apex of lung Rib Parietal pleura Pleural cavity Visceral pleura Lung Pulmonary artery Trachea Thymus Apex of lung Right superior lobe Horizontal fissure Right middle lobe Oblique fissure Left superior lobe Oblique fissure Left inferior lobe Right inferior lobe Heart (in mediastinum) Diaphragm Cardiac notch Base of lung (a) Anterior view. The lungs flank mediastinal structures laterally. Left superior lobe Left main bronchus Oblique fissure Pulmonary vein Impression of heart Oblique fissure Left inferior lobe Hilum Aortic impression Lobules (b) Photograph of medial view of the left lung Figure 22.11a, b Bronchopulmonary Segments Right lung Left lung Right superior lobe (3 segments) Left superior lobe (4 segments) Right middle lobe (2 segments) Right inferior lobe (5 segments) Figure 22.12 Left inferior lobe (5 segments) Blood Supply and Innervation of the Lungs • Pulmonary arteries – deliver oxygen-poor blood to the lungs • Pulmonary veins – carry oxygenated blood to the heart • Innervation – sympathetic, parasympathetic, and visceral sensory fibers – Parasympathetic—constrict airways – Sympathetic—dilate airways Superior Thorax Vertebra Right lung Parietal pleura Visceral pleura Pleural cavity Posterior Esophagus (in mediastinum) Root of lung at hilum Left main bronchus Left pulmonary artery Left pulmonary vein Left lung Thoracic wall Pulmonary trunk Pericardial membranes Sternum Heart (in mediastinum) Anterior mediastinum Anterior (d) Transverse section through the thorax, viewed from above. Lungs, pleural membranes, and major organs in the mediastinum are shown. Figure 22.11d The Pleurae • A double-layered sac surrounding each lung – Parietal pleura – Visceral pleura • Pleural cavity – potential space between the visceral and parietal pleurae • Pleurae help divide the thoracic cavity – Central mediastinum – Two lateral pleural compartments Diagram of the Pleurae and Pleural Cavities Intercostal muscle Rib Parietal pleura Pleural cavity Visceral pleura Lung Trachea Thymus Apex of lung Right superior lobe Horizontal fissure Right middle lobe Oblique fissure Left superior lobe Oblique fissure Left inferior lobe Right inferior lobe Heart (in mediastinum) Diaphragm Cardiac notch Base of lung (a) Anterior view. The lungs flank mediastinal structures laterally. Figure 22.11a Location of Lungs in Thoracic Cavity • Four processes involved in respiration – – – – Pulmonary ventilation External respiration Transport of respiratory gases Internal respiration Clavicle Lung Rib 3 4 Rib 8 Nipple 9 5 Lung 6 7 10 11 12 Parietal pleura 8 Midaxillary line 9 10 Midclavicular line (a) Posterior view (b) Anterior view Infrasternal Angle at xiphisternal joint Parietal pleura Costal margin Figure 22.13 The Mechanisms of Ventilation • Two phases of pulmonary ventilation – Inspiration: inhalation – Expiration: exhalation • Inspiration – volume of thoracic cavity increases – Decreases internal gas pressure – Contraction of the diaphragm (flattens) – Contraction of intercostal muscles raises the ribs • Deep inspiration requires – Scalenes, sternocleidomastoid, pectoralis minor, and erector spinae group (extends the back) Expiration • Quiet expiration—chiefly a passive process – Inspiratory muscles relax – Diaphragm moves superiorly – Volume of thoracic cavity decreases • Forced expiration—an active process – Produced by contraction of • Internal and external oblique muscles • Transverse abdominis muscles Changes in Thoracic Volume (a) Inspiration Diaphragm and intercostal muscles contract (diaphragm descends and rib cage rises). Thoracic cavity volume increases. Changes in superiorinferior and anteriorposterior dimensions Ribs are elevated and sternum flares as external intercostals contract. Diaphragm moves inferiorly during contraction. Changes in lateral dimensions (superior view) External intercostals contract. (b) Expiration Inspiratory muscles relax (diaphragm rises and rib cage descends due to recoil of the costal cartilages). Thoracic cavity volume decreases. Ribs and sternum are depressed as external intercostals relax. Diaphragm moves superiorly as it relaxes. External intercostals relax. Figure 22.14 Changes in Thoracic Volume 1 At rest, no air movement: Air pressure in lungs is equal to atmospheric (air) pressure. Pressure in the pleural cavity is less than pressure in the lungs. This pressure difference keeps the lungs inflated. Trachea Main bronchi Thoracic wall Pleural cavity Lung Lung 3 Expiration: Inspiratory muscles relax, reducing thoracic volume, and the lungs recoil. Simultaneously, volumes of the pleural cavity and the lungs decrease, causing pressure to increase in the lungs, and air flows out. Resting state is reestablished. Pleural Thoracic cavity wall Diaphragm Air 2 Inspiration: Inspiratory muscles contract and increase the volume of the thoracic and pleural cavities. Pleural fluid in the pleural cavity holds the parietal and visceral pleura close together, causing the lungs to expand. As volume increases, pressure decreases and air flows into the lungs. Parietal pleura Visceral pleura At rest V P Expanded V P Air flows in Air V P Air flows out V P Figure 22.15 Neural Control of Ventilation • Respiratory center – generates baseline respiration rate – In the reticular formation of the medulla oblongata • VRG (ventral respiratory group) – most important respiratory center – Neurons generate respiratory rhythm Respiratory Centers in the Brain Stem Pons Medulla Ventral respiratory group (VRG) contains rhythm generators whose output drives respiration. Pons Medulla To inspiratory muscles Pontine respiratory centers interact with the medullary respiratory centers to smooth the respiratory pattern. Dorsal respiratory group (DRG) integrates peripheral sensory input and modifies the rhythms generated by the VRG. Diaphragm External intercostal muscles Figure 22.16 Location of Peripheral Chemoreceptors • Chemoreceptors – Sensitive to rising and falling oxygen levels • Central chemoreceptors —located in medulla • Peripheral chemoreceptors – Aortic bodies – Carotid bodies Brain Sensory nerve fiber in cranial nerve IX (pharyngeal branch of glossopharyngeal) External carotid artery Internal carotid artery Carotid body Common carotid artery Cranial nerve X (vagus nerve) Sensory nerve fiber in cranial nerve X Aortic bodies in aortic arch Aorta Heart Figure 22.17 Disorders of Lower Respiratory Structures • Bronchial asthma – type of allergic inflammation – Hypersensitivity to irritants in the air or to stress – Asthma attacks characterized by contraction of bronchiole smooth muscle and secretion of mucus in airways • Cystic fibrosis (CF)—inherited disease – Exocrine gland function is disrupted – Respiratory system affected by oversecretion of viscous mucus • Chronic obstructive pulmonary disease (COPD) – airflow into and out of the lungs is difficult – Obstructive emphysema and chronic bronchitis – History of smoking Disorders of Lower Respiratory Structures Figure 22.18 Alveolar Changes in Emphysema Figure 22.19 Disorders of Upper Respiratory Structures • Epistaxis—nosebleed The Respiratory System Throughout Life • By week 4 of development: – Olfactory placodes appear • Invaginate to form olfactory pits – Laryngotracheal bud • Forms trachea, bronchi, and bronchi subdivisions • Reaches functional maturity late in development • At birth, only one-sixth of alveoli are present • Those who begin smoking as teenagers – Lungs never fully develop – Additional alveoli never form The Respiratory System Throughout Life Future mouth Pharynx Frontonasal elevation Eye Olfactory placode Foregut Stomodeum (future mouth) Olfactory placode Esophagus Liver (a) 4 weeks: anterior superficial view of the embryo’s head Trachea Laryngotracheal Bronchial bud buds (b) 5 weeks: left lateral view of the developing lower respiratory passageway mucosae Figure 22.20 Aging and the Respiratory System • Aging results in decreased vital capacity, decreased blood level of O2, and diminished alveolar macrophage activity • The elderly are more susceptible to pneumonia, emphysema, bronchitis, and other pulmonary disorders Aging and the Respiratory System • Emphysema (em′-fi-SĒ-ma = blown up or full of air): disorder characterized by destruction of the walls of the alveoli – Produces abnormally large air spaces that remain filled with air during exhalation – With less surface area for gas exchange, O2 diffusion across the respiratory membrane is reduced – Blood O2 level is lowered, and any mild exercise that raises the O2 requirements of the cells leaves the patient breathless – As increasing numbers of alveolar walls are damaged, lung elastic recoil decreases due to loss of elastic fibers, and an increasing amount of air becomes trapped in the lungs at the end of exhalation – Over several years, added respiratory exertion increases the size of the chest cage, resulting in a “barrel chest” – Emphysema is a common precursor to the development of lung cancer Aging of the Respiratory System • Number of glands in the nasal mucosa declines • Nose dries – produces thickened mucus • Thoracic wall becomes more rigid • Lungs lose elasticity • Oxygen levels in the blood may fall
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