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The Respiratory System Chapter 13 1 Outline • • Functions of the Respiratory System Respiratory System Anatomy – – – – – – • • Microscopic Anatomy of Alveoli Mechanics of Breathing – • • • • The Nose The Pharynx The Larynx The Trachea The Bronchi The Lungs Inspiration and Expiration Lung Volumes & Capacities Exchange of Oxygen & Carbon Dioxide Transport of Oxygen & Carbon Dioxide Control of Respiration 2 Functions of the Respiratory System • • • • • • • Gas exchange: Oxygen is brought into the body and carbon dioxide to eliminated from the body Helps maintain blood pH Cleans, warms, and moistens incoming air Provides ability to smell, protects against noxious compounds Provides ability to produce sounds, hence communicate effectively within the species Assists defense against pathogens Aids venous blood return to the heart and lymphatic fluid return to the cardiovascular system 3 The Respiratory System 4 The Respiratory System • • During inspiration or inhalation, air is conducted toward the lungs. During expiration or exhalation, air is conducted away from the lungs. 5 Figure 13.2 Basic anatomy of the upper respiratory tract, sagittal section. Respiratory System Anatomy Pharynx • Nasopharynx • Oropharynx • Laryngopharynx (a) Regions of the pharynx Cribriform plate of ethmoid bone Sphenoidal sinus Frontal sinus Nasal cavity • Nasal conchae (superior, middle and inferior) • Nasal meatuses (superior, middle, and inferior) • Nasal vestibule • Nostril Posterior nasal aperture Nasopharynx • Pharyngeal tonsil • Opening of pharyngotympanic tube • Uvula Oropharynx • Palatine tonsil • Lingual tonsil Laryngopharynx Esophagus Trachea Hard palate Soft palate Tongue Hyoid bone Larynx • Epiglottis • Thyroid cartilage • Vocal fold • Cricoid cartilage (b) Detailed anatomy of the upper respiratory tract © 2015 Pearson Education, Inc. Respiratory System Anatomy (Cont.) • The Nose – – – – – – – As air moves into the nose it is cleansed (by coarse hairs, cilia, and mucus) warmed, and moistened Special cells in upper part of cavities detect odors; olfactory epithelium Involved with modifying speech sounds; areas act as resonating chambers, e.g. paranasal sinuses Tears drain into the nasal cavities via nasolacrimal ducts Paranasal sinuses drain mucus into nasal cavities; additional mucus flow Auditory tubes (pharyngotympanic; Eustachian) lead from the nasopharynx to the middle ears Respiratory epithelium on bony folds (nasal conchae; increase surface area); produce mucus; cilia move mucus to esophagus for swallowing or spitting 7 Figure 13.2 Basic anatomy of the upper respiratory tract, sagittal section. Respiratory System Anatomy Pharynx • Nasopharynx • Oropharynx • Laryngopharynx (a) Regions of the pharynx Cribriform plate of ethmoid bone Sphenoidal sinus Frontal sinus Nasal cavity • Nasal conchae (superior, middle and inferior) • Nasal meatuses (superior, middle, and inferior) • Nasal vestibule • Nostril Posterior nasal aperture Nasopharynx • Pharyngeal tonsil • Opening of pharyngotympanic tube • Uvula Oropharynx • Palatine tonsil • Lingual tonsil Laryngopharynx Esophagus Trachea Hard palate Soft palate Tongue Hyoid bone Larynx • Epiglottis • Thyroid cartilage • Vocal fold • Cricoid cartilage (b) Detailed anatomy of the upper respiratory tract © 2015 Pearson Education, Inc. Respiratory System Anatomy (Cont.) • The Pharynx – – – – The pharynx is a funnel-shaped passageway that connects the nasal and oral cavities to the larynx. Three sections. Nasopharynx - Nasal cavities open above soft palate. Oropharynx - Oral cavity opens. The tonsils (defensive lymphatic tissue containing lymphocytes) form protective ring at junction of oral cavity with pharynx. Laryngopharynx - Opens into the larynx. In the pharynx, air and food pathways cross. Air cleansed by cilia and mucus. 9 Figure 13.2 Basic anatomy of the upper respiratory tract, sagittal section. Respiratory System Anatomy Pharynx • Nasopharynx • Oropharynx • Laryngopharynx (a) Regions of the pharynx Cribriform plate of ethmoid bone Sphenoidal sinus Frontal sinus Nasal cavity • Nasal conchae (superior, middle and inferior) • Nasal meatuses (superior, middle, and inferior) • Nasal vestibule • Nostril Posterior nasal aperture Nasopharynx • Pharyngeal tonsil • Opening of pharyngotympanic tube • Uvula Oropharynx • Palatine tonsil • Lingual tonsil Laryngopharynx Esophagus Trachea Hard palate Soft palate Tongue Hyoid bone Larynx • Epiglottis • Thyroid cartilage • Vocal fold • Cricoid cartilage (b) Detailed anatomy of the upper respiratory tract © 2015 Pearson Education, Inc. Respiratory System Anatomy (Cont.) • The Larynx (Voice Box) – – – The larynx serves as a passageway for air between the pharynx and the trachea. When food is swallowed, the larynx moves up against the epiglottis preventing food from passing into the larynx. Food moves into the esophagus. The larynx (voice box) houses the vocal cords which are stretched across the glottis. Air cleansed by cilia and mucus. 11 Figure 13.2 Basic anatomy of the upper respiratory tract, sagittal section. Respiratory System Anatomy Pharynx • Nasopharynx • Oropharynx • Laryngopharynx (a) Regions of the pharynx Cribriform plate of ethmoid bone Sphenoidal sinus Frontal sinus Nasal cavity • Nasal conchae (superior, middle and inferior) • Nasal meatuses (superior, middle, and inferior) • Nasal vestibule • Nostril Posterior nasal aperture Nasopharynx • Pharyngeal tonsil • Opening of pharyngotympanic tube • Uvula Oropharynx • Palatine tonsil • Lingual tonsil Laryngopharynx Esophagus Trachea Hard palate Soft palate Tongue Hyoid bone Larynx • Epiglottis • Thyroid cartilage • Vocal fold • Cricoid cartilage (b) Detailed anatomy of the upper respiratory tract © 2015 Pearson Education, Inc. Thyroid cartilage Cricoid cartilage Vocal fold Arytenoid cartilage Superior view of cartilages and muscles Posterior cricoarytenoid muscle View through a laryngoscope (a) Movement of vocal folds apart (abduction) Lateral cricoarytenoid muscle (b) Movement of vocal folds together (adduction) Tongue Epiglottis Glottis: Vocal folds (true vocal cords) Rima glottidis Ventricular folds (false vocal cords) Cuneiform cartilage Corniculate cartilage View Larynx Anterior Epiglottis Vocal folds (true vocal cords) Rima glottidis Cuneiform cartilage Ventricular folds (false vocal cords) Corniculate cartilage (c) Superior view Posterior Respiratory System Anatomy (Cont.) • The Trachea – – – Tube, containing C-shaped cartilage (to maintain patency during breathing), connecting larynx to primary bronchi; spanning open part of the C is fibromuscular membrane containing trachealis muscle- contraction & relaxation can change diameter slightly Pseudostratified ciliated columnar epithelium sweeps mucus up toward the pharynx (Mucus escalator) for swallowing or spitting The trachea divides into left and right primary bronchi which eventually branch into secondary bronchi and then into bronchioles 15 16 Figure 13.3a Structural relationship of the trachea and esophagus. Posterior Mucosa Submucosa Esophagus Trachealis muscle Lumen of trachea Seromucous gland in submucosa Hyaline cartilage Adventitia (a) © 2015 Pearson Education, Inc. Anterior Figure 13.3b Structural relationship of the trachea and esophagus. (b) © 2015 Pearson Education, Inc. The Trachea: Mucus escalator 19 BRANCHING OF BRONCHIAL TREE Larynx Trachea Trachea Primary bronchi Secondary bronchi Left lung Right lung Tertiary bronchi Visceral pleura Bronchioles Parietal pleura Terminal bronchioles Pleural cavity Location of carina Right primary bronchus Left primary bronchus Left secondary bronchus Right secondary bronchus Left tertiary bronchus Left bronchiole Right tertiary bronchus Right bronchiole Right terminal bronchiole Left terminal bronchiole Cardiac notch Anterior view Diaphragm Respiratory System Anatomy (Cont.) • The Lungs – – – – Each bronchiole leads to an elongated space enclosed by alveoli. The alveoli make up the lungs. The lungs lie on either side of the heart within the thoracic cavity. Right lung has three lobes and the left lung has two lobes Each lobe is divided into lobules, further divided into bronchioles serving many alveoli. Contain large quantities of elastic fibers- permit stretching- have a tendency to want to collapse Gas exchange takes place in the alveoli 21 Figure 13.4b Anatomical relationships of organs in the thoracic cavity. Vertebra Posterior Esophagus (in posterior mediastinum) Root of lung at hilum • Left main bronchus • Left pulmonary artery • Left pulmonary vein Right lung Parietal pleura Visceral pleura Left lung Pleural cavity Thoracic wall Pulmonary trunk Pericardial membranes Sternum Heart (in mediastinum) Anterior mediastinum Anterior (b) Transverse section through the thorax, viewed from above. © 2015 Pearson Education, Inc. Respiratory System Anatomy (Cont.) • Lungs (Cont.) – Microscopic anatomy Lobules- wrapped in elastic connective tissue with lymphatic vessel, arteriole, venule, & a terminal bronchiole Terminal bronchiole lead to respiratory bronchioles (have alveoli budding on surface), then to alveolar ducts, then to alveolar sacs, then alveoli All gas exchange occurs in alveoli 23 MICROSCOPIC AIRWAYS Terminal bronchioles Terminal bronchiole Respiratory bronchioles Alveolar ducts Pulmonary Alveolar sacs arteriole Lymphatic Alveoli vessel Respiratory bronchiole Alveoli Pulmonary venule Elastic connective tissue Pulmonary capillary Visceral pleura Alveolar ducts Alveolar sac Alveoli (a) Diagram of portion of lobule of lung Respiratory System Anatomy (Cont.) • Lungs (Cont.) – Microscopic anatomy Alveoli Wall composed of Type I alveolar cells- simple squamous epithelium- main site of gas exchange Type II alveolar cells- produce alveolar fluid containing surfactant- extremely important mixture of phospholipids & lipoproteins- lower surface tension due to hydrogen bonding of water molecules-prevents collapse of the alveoli Alveolar macrophages- remove particular debris Respiratory membrane- type I alveolar cells, their basement membrane; capillary basement membrane, capillary endothelial cells 25 Monocyte Reticular fiber Elastic fiber Type II alveolar (septal) cell Respiratory membrane Alveolus Type I alveolar cell Diffusion of O2 Diffusion of CO2 Alveolar macrophage (dust cell) Alveolus Red blood cell in pulmonary capillary Red blood cell Capillary endothelium Capillary basement membrane Epithelial basement membrane Type I alveolar cell Interstitial space Alveolar fluid with surfactant (a) Section through alveolus showing cellular components (b) Details of respiratory membrane Figure 13.6 Anatomy of the respiratory membrane (air-blood barrier). Red blood cell Capillary Endothelial cell nucleus Alveolar pores Capillary O2 CO2 Macrophage Nucleus of squamous epithelial cell Respiratory membrane Alveolus Alveolar epithelium Fused basement membranes Capillary endothelium Alveoli (gasfilled air spaces) Squamous Red blood Surfactantcell in secreting cell epithelial cell of alveolar wall capillary © 2015 Pearson Education, Inc. Ventilation: Inspiration and Expiration • • • Normally there is a continuous column of air from the pharynx to the alveoli. Lungs lie within sealed thoracic cavity. – Rib cage forms top and side of the cavity, while the diaphragm forms the floor. Thoracic cavity and lungs are enclosed by two membranes, pleura. – Visceral pleura surround the lungs – Parietal pleura sticks to the rib cage and diaphragm. – Fluid separates these two. Pressure in fluid is normally negative due to lungs trying to collapse (elastic recoil). 28 Inspiration • • A respiratory center located in the brain triggers inspiration. Inspiration is the active phase of breathing. – The diaphragm and the rib muscles (intercostals) contract, intrapleural pressure decreases, the lungs expand, and air rushes in. Creation of a partial vacuum in the alveoli causes air to enter the lungs. 29 Inspiration Versus Expiration 30 Figure 13.7 Rib cage and diaphragm positions during breathing. Changes in anterior-posterior and superior-inferior dimensions Changes in lateral dimensions Ribs elevated as external intercostals contract External intercostal muscles Full inspiration (External intercostals contract) Diaphragm moves inferiorly during contraction (a) Inspiration: Air (gases) flows into the lungs Ribs depressed as external intercostals relax External intercostal muscles Diaphragm moves superiorly as it relaxes (b) Expiration: Air (gases) flows out of the lungs © 2015 Pearson Education, Inc. Expiration (External intercostals relax) Pressure relative to atmospheric pressure Figure 13.8 Changes in intrapulmonary pressure and air flow during inspiration and expiration. +2 +1 Inspiration Expiration Intrapulmonary pressure 0 −1 −2 (a) Volume of breath Volume (L) 0.5 0 −0.5 (b) © 2015 Pearson Education, Inc. Expiration • • When the respiratory center stops sending signals to the diaphragm and the rib cage, the diaphragm relaxes. – Abdominal organs press up against the diaphragm, and the rib cage moves down and inward. Expiration is usually passive as the diaphragm and intercostal muscles are relaxed and the lung tissue recoils. 33 Inspiration Versus Expiration 34 Figure 13.7 Rib cage and diaphragm positions during breathing. Changes in anterior-posterior and superior-inferior dimensions Changes in lateral dimensions Ribs elevated as external intercostals contract External intercostal muscles Full inspiration (External intercostals contract) Diaphragm moves inferiorly during contraction (a) Inspiration: Air (gases) flows into the lungs Ribs depressed as external intercostals relax External intercostal muscles Diaphragm moves superiorly as it relaxes (b) Expiration: Air (gases) flows out of the lungs © 2015 Pearson Education, Inc. Expiration (External intercostals relax) Pressure relative to atmospheric pressure Figure 13.8 Changes in intrapulmonary pressure and air flow during inspiration and expiration. +2 +1 Inspiration Expiration Intrapulmonary pressure 0 −1 −2 (a) Volume of breath Volume (L) 0.5 0 −0.5 (b) © 2015 Pearson Education, Inc. Lung Volumes & Capacities • Spirometer- generates spirogram 1. 2. 3. 4. 5. 6. 7. Tidal volume (TV)= mL/breath Anatomic dead space- 30% of TV Inspiratory reserve volume (IRV) Expiratory reserve volume (ERV) Residual volume Vital capacity (VC) Total lung capacity 37 Figure 13.9 Idealized tracing of the various respiratory volumes of a healthy young adult male. 6,000 Milliliters (ml) 5,000 4,000 Inspiratory reserve volume 3,100 ml 3,000 2,000 1,000 0 © 2015 Pearson Education, Inc. Tidal volume 500 ml Expiratory reserve volume 1,200 ml Residual volume 1,200 ml Vital capacity 4,800 ml Total lung capacity 6,000 ml Exchange of Oxygen & Carbon Dioxide • Gas laws: Dalton’s law & Henry’s law – – • Dalton’s law- each gas in a mixture exerts it’s own pressure independent of the other gas- this pressure is called it’s partial pressure (in mmHg) Henry’s law- quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas & to it’s solubility- solubility of CO2 is 24 times greater than the solubility of O2 in water External & internal respiration- exchange of gases between alveolar air & blood – Dependent on 1. Partial pressure difference of the gases- the larger the partial pressure difference of O2 in alveolar air vs. partial pressure in the blood, the greater the rate of diffusion; the larger the partial pressure of CO2 in the blood vs. the partial pressure in the alveolar air, the greater the rate of diffusion 39 Exchange of Oxygen & Carbon Dioxide (Cont.) • External & internal respiration (Cont.) 2. Surface area available for gas exchange- normally 750 ft2 ; any disorder that decreases functional surface area decreases rate of exchange (e.g. emphysema; destruction of alveolar walls 3. Diffusion distance- respiratory membrane very thin (just two cells thick); RBCs moving through capillaries in single file; slow blood flow through capillaries; any disease that builds up interstitial fluid slows rate of exchange (e.g. asthma, pulmonary edema) 4. Molecular weight & solubility of the gases- O2 is smaller but CO2 is 24 times more soluble- net is that CO2 diffusion is ~20 times faster than O2 ; thus in disease states hypoxia comes before hypercapnia 40 CO2 exhaled O2 inhaled Atmospheric air: PO2 = 159 mmHg PCO2 = 0.3 mmHg Alveoli Alveolar air: PO2 = 105 mmHg PCO2 = 40 mmHg CO2 O 2 Pulmonary capillaries To lungs (a) External respiration: pulmonary gas exchange To left atrium Deoxygenated blood: PO2 = 40 mmHg PCO2 = 45 mmHg Oxygenated blood: PO2 = 100 mmHg PCO2 = 40 mmHg To right atrium To tissue cells (b) Internal respiration: systemic gas exchange Systemic capillaries CO2 O2 Systemic tissue cells: PO2 = 40 mmHg PCO2 = 45 mmHg Figure 13.10 Gas exchanges in the body occur according to the laws of diffusion. Inspired air: Alveoli of lungs: CO2 O2 O2 CO2 O2 CO2 External respiration Pulmonary arteries Alveolar capillaries Blood leaving tissues and entering lungs: Pulmonary veins Blood leaving lungs and entering tissue capillaries: Heart O2 CO2 Tissue capillaries Systemic veins Internal respiration Systemic arteries CO2 O2 Tissue cells: O2 CO2 © 2015 Pearson Education, Inc. O2 CO2 Transport of Oxygen & Carbon Dioxide • Oxygen transport- hemoglobin (Hb) – Hb + O2 = Hb-O2 (oxyhemoglobin); reversible Relationship between hemoglobin & oxygen partial pressure As partial pressure of O2 increases have rapid binding to Hb but then binding plateaus & reaches saturation At 100 mmHg, 100% saturation of Hb 43 Transport of Oxygen & Carbon Dioxide (Cont.) • Carbon dioxide transport 1. 2. Dissolved CO2 – 7% is dissolved in plasma Carbamino compounds- 23% bound to Hb; higher the partial pressure of CO2 the greater the binding Hb + CO2 = Hb-CO2 ; reversible Binds to terminal amino acids of globin portions of Hb 3. Bicarbonate ions- 70%- generated by equation belowcarried inside RBCs CA Hydrogen Ion Bicarbonate Ion Carbonic Acid Carbon Dioxide 44 Figure 13.11 Diagrammatic representation of the major means of oxygen (O 2) and carbon dioxide (CO2) loading and unloading in the body. (a) External respiration in the lungs (pulmonary gas exchange) Oxygen is loaded into the blood and carbon dioxide is unloaded. (b) Internal respiration in the body tissues (systemic capillary gas exchange) Oxygen is unloaded and carbon dioxide is loaded into the blood. Alveoli (air sacs) Tissue cells O2 Loading of O2 Hb + O2 HbO2 (Oxyhemoglobin is formed) CO2 CO2 Loading of CO2 Unloading of CO2 HCO3− + H+ H2CO3 CO2 + H2O BicarCarbonic Water bonate acid ion O2 Unloading of O2 CO2 + H2O H2CO3 H++ HCO3− Water Carbonic Bicaracid bonate ion Plasma HbO2 Hb + O2 Plasma Red blood cell Systemic capillary Pulmonary capillary © 2015 Pearson Education, Inc. Red blood cell Control of Respiration • Respiratory Center- control rate & depth of breathing – Three important areas in brain stem 1. 2. 3. 1. Medullary rhythmicity area- medulla oblongata Pneumotaxic area- upper pons Apneustic area- lower pons Medullary rhythmicity area- controls the basic rhythm of respiration 2. Pneumotaxic area- sends inhibitory signals to the inspiratory area of the medulla oblongata; prevents over expansion of lungs 3. Apneustic area- sends stimulatory signals to the inspiratory area of the medulla oblongata; activates it; prolongs inhalation, result is long deep inhalations; overridden by the pneumotaxic area when active 46 Figure 13.12 Breathing control centers, sensory inputs, and effector nerves. Breathing control centers: • Pons centers • Medulla centers Efferent nerve impulses from medulla trigger contraction of inspiratory muscles. • Phrenic nerves • Intercostal nerves Afferent impulses to medulla Breathing control centers stimulated by: CO2 increase in blood (acts directly on medulla centers by causing a drop in pH) Nerve impulse from O2 sensor indicating O2 decrease Intercostal muscles Diaphragm O2 sensor in aortic body of aortic arch © 2015 Pearson Education, Inc. Control of Respiration (Cont.) • Respiratory Center (Cont.) – Regulation of the respiratory center 1. 2. 3. 4. 5. Cortical influence on respiration Chemoreceptor regulation of respiration Proprioceptor stimulation of respiration The inflation reflex Other influence on respiration a) b) c) d) e) f) Limbic system stimulation Temperature Pain Stretching of the anal sphincter Irritation of airways Blood pressure 48 Control of Respiration (Cont.) • Respiratory Center (Cont.) – Regulation of the respiratory center (Cont.) 1. 2. Cortical influence on respiration- cerebral cortex connected to the respiratory center- can voluntarily alter breathing patterns- provides voluntary protect effect; input from hypothalamic & limbic systems- emotional stimuli can alter breathing, e.g. laughing & crying Chemoreceptor regulation of respiration- very sensitive to CO2 & O2 levels Two locations a) Central chemoreceptors- in medulla oblongatarespond to changes H+ & partial pressure of CO2 b) Peripheral chemoreceptors- PCO2 , H+ , PO2 Carotid bodies- most sensitive to PCO2 Aortic bodies- most sensitive to PCO2 49 Figure 13.12 Breathing control centers, sensory inputs, and effector nerves. Breathing control centers: • Pons centers • Medulla centers Efferent nerve impulses from medulla trigger contraction of inspiratory muscles. • Phrenic nerves • Intercostal nerves Afferent impulses to medulla Breathing control centers stimulated by: CO2 increase in blood (acts directly on medulla centers by causing a drop in pH) Nerve impulse from O2 sensor indicating O2 decrease Intercostal muscles Diaphragm O2 sensor in aortic body of aortic arch © 2015 Pearson Education, Inc. Medulla oblongata Sensory axons in glossopharyngeal nerve (cranial nerve IX) Internal carotid artery External carotid artery Carotid body Carotid sinus Sensory axons in vagus nerve (cranial nerve X) Common carotid artery Arch of aorta Aortic bodies Heart Some stimulus disrupts homeostasis by Increasing Arterial blood PCO2 (or decreasing pH or PO2) Receptors Central Chemoreceptors in medulla Peripheral chemoreceptors in aortic and carotid bodies Nerve impulses Input Control center Inspiratory area in medulla oblongata Output Nerve impulses Effectors Muscles of inhalation and exhalation contract more forcefully and more frequently (hyperventilation) Decrease in arterial blood PCO2, increase in pH, and increase in PO2 Return to homeostasis when response brings arterial blood PCO2 , pH, and PO2 back to normal Control of Respiration (Cont.) • Respiratory Center (Cont.) – Regulation of the respiratory center (Cont.) 3. 4. Proprioceptor stimulation of respiration- start exercising get increase in respiration depth & rate before changes in PCO2 , H+ , PO2 , due to input from proprioceptors directly into inspiratory area of medulla oblongata The inflation reflex- stretch receptors in bronchi & bronchioles- overinflation causes signals to inspiratory & apneustic areas, inhibition of both areas, exhalation begins- protects from overinflation (not part normal regulation) 53 Control of Respiration (Cont.) • Respiratory Center (Cont.) – Regulation of the respiratory center (Cont.) 5. Other influence on respiration a) Limbic system stimulation- emotional anxiety resulting in excitatory stimuli- rate & depth of breathing go up b) Temperature- increase temperature increase rate; decrease temperature decrease rate c) d) e) f) Pain- sudden severe pain can stop breathing briefly (apnea); prolonged somatic pain increases rate; visceral pain can slow rate Stretching of the anal sphincter- increases rate Irritation of airways- chemical or physical irritation of pharynx or larynx cause immediate cessation of breathing Blood pressure- carotid & aortic baroreceptors for blood pressure control have small effect on breathing rate; rise in blood pressure decrease rate; drop in pressure increases rate 54 Need to Know Functions of the Respiratory System 1. a) b) c) d) e) Gas exchange: oxygen in, CO2 out Aids venous and lymph return Assists defense Cleans, warms, moistens air Help maintain pH Components of the Respiratory System 2. a) b) c) d) Nose: cleans, warms, moistens air, detects odors Pharynx: connects nose, mouth, larynx; tonsils aid defense; food and air paths cross Auditory tube (Eustachian): tube from middle ear to pharynx; equalizes air pressure on both sides of eardrum (covered in Sensory Mechanisms Chap. 12) Larynx: voice box, allows speech; closes off during swallowing 55 Need to Know (Cont.) Components of the Respiratory System (Cont.) 2. e) f) g) h) Trachea (C-shaped cartilage holds this tube open), bronchi (has smooth muscle), bronchioles (little smooth muscle): tubes conducting air to alveoli; mucus escalator in trachea aids in defense Alveoli: area of gas exchange Capillaries lay right up against the walls of the alveoli; walls of the alveoli are only one cell thick Exchange of gases Oxygen diffuses through the alveoli walls and the walls of the capillaries (which are also only one cell thick) and enters into red blood cells and then binds to hemoglobin Carbon dioxide, carried mostly inside RBC as bicarbonate ion; small amount of CO2 carried on hemoglobin; bicarbonate ion converted to CO2 which then diffuses out of the capillaries and enters into the air in the alveoli to be expelled 56 Need to Know (Cont.) Inspiration and Expiration 3. a) b) c) d) Negative pressure in thoracic cavity due to elastic tissue in lungs tending to collapse the lungs Parietal pleura (membrane; epithelial cell layer) on wall of thoracic cavity Visceral pleura (membrane; epithelial cell layer) on surface of lung tissue Fluid layer between the two pleural membranes; prevents collapse of lung due to hydrogen bonding of the water molecules in the fluid to each membrane surface 57 Need to Know (Cont.) Inspiration and Expiration (Cont.) 3. e) Inspiration: active process; rib cage lifted up and out by intercostal muscles while diaphragm (large muscle that makes up the floor of the thoracic cavity) flattens, pushing the abdominal cavity downward; result is large increase in size of the cavity with the lung stuck to it by hydrogen bonding of water molecules; air is now in larger space thus pressure of the air in the lungs decreases; air from outside then rushes in to equalize the pressure 58 Need to Know (Cont.) Inspiration and Expiration (Cont.) 3. Expiration: mostly passive; intercostal muscles relax, diaphragm relaxes, thus rib cage gets smaller, diaphragm now moves back up into the thoracic cavity; air in lungs is now in smaller space then before thus pressure increases and then it moves out of the lungs Control of Respiration a) Know that the principal mechanism for control of respiration is the chemoreceptors in the carotid & aortic bodies and the amount of CO2 in the blood and the blood pH, which is directly related to the amount of CO2 in the blood f) 4. 59