The Respiratory System 22 The Respiratory System

The Respiratory System Basic functions of the respiratory system Supplies body with oxygen Disposes of carbon dioxide Four processes involved in respiration Pulmonary ventilation External respiration Transport of respiratory gases Internal respiration

Functional Anatomy of the Respiratory System Respiratory organs Nose, nasal cavity, and paranasal sinuses Pharynx, larynx, and trachea Bronchi and smaller branches Lungs and alveoli

Organs of the Respiratory System Nasal cavity Trachea Carina of trachea Left main (primary) bronchus Right main Right lung Parietal pleura Left lung Alveoli Bronchi Nostril Oral cavity Pharynx Larynx Diaphragm Figure 22.1

Organs of the Respiratory System Divided into Conducting zone Respiratory zone

The Nose Provides an airway for respiration Moistens and warms air Filters inhaled air Resonating chamber for speech Houses olfactory receptors

Size variation due to differences in nasal cartilages The Nose Size variation due to differences in nasal cartilages Skin is thin—contains many sebaceous glands Frontal bone Nasal bone Septal cartilage Maxillary bone (frontal process) Lateral process of septal cartilage Minor alar cartilages Major alar Dense fibrous connective tissue (b) External skeletal framework Epicranius, frontal belly Ala of nose Root and bridge of nose Dorsum nasi Apex of nose Philtrum Naris (nostril) (a) Surface anatomy Figure 22.2

External nares—nostrils Divided by nasal septum The Nasal Cavity External nares—nostrils Divided by nasal septum Continuous with nasopharynx Posterior nasal apertures—choanae

Two types of mucous membrane Nasal Cavity Two types of mucous membrane Olfactory mucosa Near roof of nasal cavity Houses olfactory (smell) receptors Respiratory mucosa Lines nasal cavity Epithelium is pseudostratified ciliated columnar

The Upper Respiratory Tract Sphenoid sinus Frontal sinus Nasal meatuses (superior, middle, and inferior) Nasopharynx Uvula Palatine tonsil Isthmus of the fauces Posterior nasal aperture Opening of pharyngotympanic tube Pharyngeal tonsil Oropharynx Laryngopharynx Vocal fold Esophagus (c) Illustration Nasal conchae (superior, middle Nasal vestibule Nostril Nasal cavity Hard palate Soft palate Tongue Lingual tonsil Epiglottis Hyoid bone Larynx Thyroid cartilage Vestibular fold Cricoid cartilage Thyroid gland Trachea Cribriform plate of ethmoid bone Figure 22.3c

Cilia move contaminated mucus posteriorly Respiratory Mucosa Consists of Pseudostratified ciliated columnar epithelium Goblet cells within epithelium Underlying layer of lamina propria Cilia move contaminated mucus posteriorly

Superior and middle nasal conchae Inferior nasal conchae Part of the ethmoid bone Inferior nasal conchae Separate bone Project medially from the lateral wall of the nasal cavity Particulate matter Deflected to mucus-coated surfaces

Funnel-shaped passageway Connects nasal cavity and mouth The Pharynx Funnel-shaped passageway Connects nasal cavity and mouth Divided into three sections by location Nasopharynx Oropharynx Laryngopharynx Type of mucosal lining changes along its length

Superior to the point where food enters Only an air passageway The Nasopharynx Superior to the point where food enters Only an air passageway Closed off during swallowing Pharyngeal tonsil (adenoids) Located on posterior wall Destroys entering pathogens Contains the opening to the pharyngotympanic tube (auditory tube) Tubal tonsil Provides some protection from infection

Arch-like entranceway—fauces Epithelium The Oropharynx Arch-like entranceway—fauces Extends from soft palate to the epiglottis Epithelium Stratified squamous epithelium Two types of tonsils in the oropharynx Palatine tonsils—in the lateral walls of the fauces Lingual tonsils—covers the posterior surface of the tongue

Passageway for both food and air Epithelium The Laryngopharynx Passageway for both food and air Epithelium Stratified squamous epithelium Continuous with the esophagus and larynx

The Larynx Three functions Voice production Provides an open airway Routes air and food into the proper channels Superior opening is Closed during swallowing Open during breathing

Nine Cartilages of the Larynx Thyroid cartilage Shield-shaped, forms laryngeal prominence (Adam’s apple) Three pairs of small cartilages Arytenoid cartilages Corniculate cartilages Cuneiform cartilages Epiglottis Tips inferiorly during swallowing

Vocal ligaments of the larynx Vocal folds (true vocal cords) Act in sound production Vestibular folds (false vocal cords) No role in sound production Epithelium of the larynx Stratified squamous—superior portion Pseudostratified ciliated columnar—inferior portion

Anatomy of the Larynx Figure 22.5a, b Body of hyoid bone Cricoid cartilage Laryngeal prominence (Adam’s apple) Clavicle Sternal head Clavicular head Sternocleidomastoid Jugular notch (a) Surface view Body of hyoid bone Epiglottis Cricoid cartilage Tracheal cartilages Thyroid cartilage Laryngeal prominence (Adam’s apple) Cricothyroid ligament Cricotracheal ligament (b) Anterior view Thyrohyoid membrane Figure 22.5a, b

Anatomy of the Larynx Figure 22.5c, d Epiglottis Hyoid bone Thyrohyoid Thyroid cartilage Glottis (c) Photograph of cartilaginous framework of the larynx, posterior view Epiglottis Corniculate cartilage Arytenoid cartilage Cricoid cartilage Tracheal cartilages Thyrohyoid membrane Epiglottis Body of hyoid bone Thyrohyoid membrane Vestibular fold (false vocal cord) Vocal fold (true vocal cord) Cricothyroid ligament Cricotracheal ligament Fatty pad Thyroid cartilage Cuneiform cartilage Corniculate cartilage Arytenoid cartilage Cricoid cartilage Tracheal cartilages Arytenoid muscle (d) Sagittal section (anterior on the right) Thyrohyoid membrane Figure 22.5c, d

Movements of the Vocal Folds (a) Vocal folds in closed position; closed glottis (b) Vocal folds in open position; open glottis Base of tongue Epiglottis Vestibular fold (false vocal cord) Vocal fold (true vocal cord) Glottis Inner lining of trachea Cuneiform cartilage Corniculate cartilage Thyroid cartilage Cricoid cartilage Vocal ligaments of vocal cords Lateral cricoarytenoid muscle Arytenoid cartilage Posterior Anterior Figure 22.6

Sphincter function of the larynx Innervation of the larynx Voice production Length of the vocal folds changes with pitch Loudness depends on the force of air across the vocal folds Sphincter function of the larynx Valsalva’s maneuver—straining Innervation of the larynx Recurrent laryngeal nerves (branch of vagus)

Descends into the mediastinum The Trachea Descends into the mediastinum C-shaped cartilage rings keep airway open Carina Marks where trachea divides into two primary bronchi Epithelium Pseudostratified ciliated columnar

The Trachea Figure 22.7 Mucosa Pseudostratified ciliated columnar (b) Photomicrograph of the tracheal wall (250) Hyaline cartilage Lamina propria (connective tissue) Submucosa Mucosa Seromucous gland in submucosa Pseudostratified ciliated columnar epithelium (a) Cross section of the trachea and esophagus Hyaline cartilage Submucosa Mucosa Seromucous gland in submucosa Posterior Lumen of trachea Anterior Esophagus Trachealis muscle Adventitia Figure 22.7

Bronchi in the Conducting Zone Bronchial tree Extensively branching respiratory passageways Primary bronchi (main bronchi) Largest bronchi Right main bronchi Wider and shorter than the left

Bronchi in the Conducting Zone Trachea Superior lobe of right lung Middle lobe Inferior lobe of left lung Left main (primary) bronchus Lobar (secondary) Segmental (tertiary) (a) The branching of the bronchial tree Figure 22.8a

Bronchi in the Conducting Zone Mucosa Pseudostratified epithelium Lamina propria Fibromusculo- cartilaginous layer Cartilage plate Smooth muscle Lumen (b) Photomicrograph of a bronchus (13) Figure 22.8b

Bronchi in the Conducting Zone Secondary (lobar) bronchi Three on the right Two on the left Tertiary (segmental) bronchi Branch into each lung segment Bronchioles Little bronchi, less than 1 mm in diameter Terminal bronchioles Less than 0.5 mm in diameter

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 Lead to alveolar sacs

Structures of the Respiratory Zone Alveolar duct Alveoli Alveolar sac Respiratory bronchioles Terminal bronchiole (a) Figure 22.9a

Structures of the Respiratory Zone Alveolar pores duct Respiratory bronchiole Alveoli 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

Structures of the Respiratory Zone Structure of alveoli Type I cells—single layer of simple squamous epithelial cells Surrounded by basal lamina Alveolar and capillary walls plus their basal lamina form Respiratory membrane

Structures of the Respiratory Zone Structures of alveoli (continued) Type II cells—scattered among type I cells Are cuboidal epithelial cells Secrete surfactant Reduces surface tension within alveoli Alveolar macrophages

Anatomy of Alveoli and the Respiratory Membrane Elastic fibers (a) Diagrammatic view of capillary-alveoli relationships Smooth muscle Alveolus Capillaries Terminal bronchiole Respiratory bronchiole Figure 22.10a, b

Anatomy of Alveoli and the Respiratory Membrane Alveolus Capillary Type II (surfactant- secreting) cell Type I cell of alveolar wall Endothelial cell nucleus Macrophage Alveoli (gas-filled air spaces) Red blood cell in capillary Alveolar pores Capillary endothelium Fused basement membranes of the alveolar epithelium and the capillary endothelium Alveolar epithelium Respiratory membrane Red blood cell O2 CO2 Nucleus of type I (squamous epithelial) cell (c) Detailed anatomy of the respiratory membrane Figure 22.10c

The Respiratory Zone Features of alveoli Surrounded by elastic fibers Interconnect by way of alveolar pores Internal surfaces A site for free movement of alveolar macrophages

Gross Anatomy of the Lungs Major landmarks of the lungs Apex, base, hilum, and root Left lung Superior and inferior lobes Fissure—oblique Right lung Superior, middle, and inferior lobes Fissures—oblique and horizontal

Gross Anatomy of the Lungs Anterior View of Thoracic Structures Trachea Apex of lung Thymus Right superior lobe Horizontal fissure Right middle lobe Oblique fissure Right inferior lobe Heart (in mediastinum) Diaphragm Base of lung Left superior lobe Cardiac notch Oblique fissure Left inferior lobe Lung Pleural cavity Parietal pleura Rib Intercostal muscle Visceral pleura (a) Anterior view. The lungs flank mediastinal structures laterally. Left superior lobe Oblique fissure Left inferior lobe (b) Photograph of medial view of the left lung Left main bronchus Pulmonary vein Impression of heart Lobules artery Apex of lung Hilum Aortic impression Figure 22.11a, b

Bronchopulmonary Segments Right superior lobe (3 segments) middle lobe (2 inferior lobe (5 segments) Left superior lobe (4 segments) Left inferior Right lung Left lung Figure 22.12

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

Transverse Cut through the Superior Thorax (d) Transverse section through the thorax, viewed from above. Lungs, pleural membranes, and major organs in the mediastinum are shown. Esophagus (in mediastinum) Right lung Parietal pleura Visceral pleura Pleural cavity Pericardial membranes Sternum Anterior Posterior Vertebra Root of lung at hilum Left lung Thoracic wall Pulmonary trunk Heart (in mediastinum) Anterior mediastinum Left main bronchus Left pulmonary artery Left pulmonary vein Figure 22.11d

A double-layered sac surrounding each lung 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 Trachea Apex of lung Thymus Right superior lobe Horizontal fissure Right middle lobe Oblique fissure Right inferior lobe Heart (in mediastinum) Diaphragm Base of lung Left superior lobe Cardiac notch Oblique fissure Left inferior lobe Lung Pleural cavity Parietal pleura Rib Intercostal muscle Visceral pleura (a) Anterior view. The lungs flank mediastinal structures laterally. Figure 22.11a

Location of Lungs in Thoracic Cavity Rib (a) Posterior view Lung 10 11 12 9 8 (b) Anterior view Clavicle Nipple Midaxillary line Midclavicular line Infrasternal angle at the xiphisternal joint Costal margin Parietal pleura Rib 3 7 6 5 4 Figure 22.13

The Mechanisms of Ventilation Two phases of pulmonary ventilation Inspiration—inhalation Expiration—exhalation

Volume of thoracic cavity increases Inspiration Volume of thoracic cavity increases Decreases internal gas pressure Action of the diaphragm Diaphragm flattens Action of intercostal muscles Contraction raises the ribs

Deep inspiration requires Scalenes Sternocleidomastoid Pectoralis minor Erector spinae—extends the back

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 Ribs are elevated and sternum flares as external intercostals contract. Diaphragm and intercostal muscles contract (diaphragm descends and rib cage rises). Thoracic cavity volume increases. Diaphragm moves inferiorly during contraction. External Changes in superior- inferior and anterior- posterior dimensions Changes in lateral (superior view) (a) Inspiration 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. External Diaphragm moves superiorly as it relaxes. (b) Expiration Figure 22.14

Changes in Thoracic Volume 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. 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. 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. Trachea Diaphragm Lung Air flows in Air flows out V P Pleural cavity Thoracic wall Air Main bronchi Parietal pleura Visceral Thoracic wall At rest Expanded 1 2 3 Figure 22.15

Neural Control of Ventilation Most important respiratory center VRG—ventral respiratory group Located in reticular formation in the medulla oblongata Neurons generate respiratory rhythm

Respiratory Centers in the Brain Stem Pons Ventral respiratory group (VRG) contains rhythm generators whose output drives respiration. Pontine respiratory centers interact with the medullary respiratory centers to smooth the respiratory pattern. Medulla To inspiratory muscles External intercostal Diaphragm Dorsal respiratory group (DRG) integrates peripheral sensory input and modifies the rhythms generated by the VRG. Figure 22.16

Neural Control of Ventilation Respiratory center Generates baseline respiration rate In the reticular formation of the medulla oblongata Chemoreceptors Sensitive to rising and falling oxygen levels Central chemoreceptors—located in medulla Peripheral chemoreceptors Aortic bodies Carotid bodies

Location of Peripheral Chemoreceptors 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 A type of allergic inflammation Hypersensitivity to irritants in the air or to stress Asthma attacks characterized by Contraction of bronchiole smooth muscle Secretion of mucus in airways

Disorders of Lower Respiratory Structures Cystic fibrosis (CF)—inherited disease Exocrine gland function is disrupted Respiratory system affected by Oversecretion of viscous mucus

Disorders of Lower Respiratory Structures Chronic obstructive pulmonary disease (COPD) Airflow into and out of the lungs is difficult Obstructive emphysema 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 Frontonasal elevation Olfactory placode Stomodeum (future mouth) Future mouth Eye Trachea Bronchial buds Pharynx Foregut Olfactory placode Esophagus Liver Laryngotracheal bud (a) 4 weeks: anterior superficial view of the embryo’s head (b) 5 weeks: left lateral view of the developing lower respiratory passageway mucosae Figure 22.20

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