Bio169 Chapter 23 Respiratory System PDF

Chapter 23 Respiratory System BIO-169  23.1 Anatomy of the Respiratory System Structures used to acquire oxygen and remove carbon dioxide from the blood. Seven structures include: External nose – for air inspiration Nasal cavity – clean, warm, and humidify air Pha...

Chapter 23 Respiratory System BIO-169  23.1 Anatomy of the Respiratory System Structures used to acquire oxygen and remove carbon dioxide from the blood. Seven structures include: External nose – for air inspiration Nasal cavity – clean, warm, and humidify air Pharynx – common passageway for food and air Larynx – voice box; keeps airway patent Trachea – air cleaning tube into the lungs Bronchi – tubes that direct air into the lungs Lungs – network of alveoli and capillaries for gas exchange 2 23.1 Anatomy of the Respiratory System Upper tract: nose, pharynx and associated structures Lower tract: larynx, trachea, bronchi, lungs and the tubing within the lungs 23-3  Nose and Nasal Cavities External nose Pharyngeal tonsil Opening of auditory tube Nasal cavity Cribriform plate – Nares: entrance to Superior concha Nasopharynx Middle concha Soft palate nasal cavity Nasal Inferior Uvula Pharynx cavity (nostrils) concha Vestibule Oropharynx Naris Laryngopharynx – Vestibule: just Hard palate inside nares Oral cavity Tongue – Hard palate: floor Palatine tonsil of nasal cavity Lingual tonsil – Nasal septum: Epiglottis partition dividing cavity. Larynx Vestibular fold Vocal fold – Concha: bony Thyroid cartilage ridges on lateral Cricoid cartilage walls with Esophagus meatuses between. Trachea (b) Medial view 23-4  Pharynx Common opening for Pharyngeal tonsil digestive and respiratory Opening of auditory tube systems Cribriform plate Three regions Superior concha Nasopharynx Middle concha Soft palate – NasopharynxNasal Inferior Uvula Pharynx cavity concha Oropharynx – Oropharynx Vestibule Naris Laryngopharynx – Laryngopharynx Hard palate Oral cavity Tongue Palatine tonsil Lingual tonsil Epiglottis Larynx Vestibular fold Vocal fold Thyroid cartilage Cricoid cartilage Esophagus Trachea (b) Medial view 23-5  Larynx Unpaired cartilages – Thyroid: largest, Adam’s apple – Cricoid: most inferior, base of larynx – Epiglottis: attached to thyroid and has a flap near base of tongue. Elastic rather than hyaline cartilage Paired – Arytenoids: attached to cricoid – Corniculate: attached to arytenoids – Cuneiform: contained in mucous membrane Ligaments extend from arytenoids to thyroid cartilage – Vestibular folds or false vocal folds – True vocal cords or vocal folds: sound production. Opening between the cords is called the glottis 23-6  Larynx Larynx Epiglottis Epiglottis Hyoid bone Hyoid bone Superior Cuneiform Adipose thyroid cartilage tissue notch Thyroid Corniculat Thyroid cartilage e cartilage cartilage Vestibular Cricoid Arytenoid cartilage fold (false cartilage vocal cord) Vocal fold Tracheal Cricoid (true vocal cartilage cartilage Trachea cord) Membranous part of trachea (a) Anterior view (b) Posterior view (c) Medial view of sagittal section 23-7  Vocal Folds Anterior Tongue Epiglottis Vestibular folds (false vocal cords) Glottis Vocal folds (true vocal cords) Cuneiform Larynx cartilage Corniculate cartilage Trachea (b) View through a laryngoscope (a) Superior view Thyroid cartilage Vocal fold Arytenoid cartilage (c) Vocal folds positioned (d) Vocal folds positioned (e) Changing the tension for breathing for speaking of the vocal folds b: © CNRI/Phototake.com 23-8  Trachea Membranous tube of dense regular connective tissue and smooth muscle Supported by 15-20 hyaline cartilage C- shaped rings open posteriorly. Posterior surface is elastic ligamentous membrane and bundles of smooth muscle called the trachealis. Contracts during coughing. Inner lining: pseudostratified ciliated columnar epithelium with goblet cells. – Mucus traps debris, cilia push it superiorly toward larynx and pharynx. 23-9  Trachea Esophagus Lumen Trachea Esophagus Transverse plane through trachea Trachealis and esophagus muscle Lumen of trachea Cartilage Mucous membrane Anterior (a) LM 250x Anterior Mucus layer Movement of mucus Cilia to pharynx Goblet cell Foreign Ciliated particle columnar epithelial cell Lamina propria (b) (c) a: © John Cunningham/Visuals Unlimited; c: © Ed Reschke/Peter Arnold, Inc./Getty 23-10 Images  Tracheobronchial Tree Trachea to terminal bronchioles which is ciliated for removal of debris. – Trachea divides to form the Left and right primary bronchi Carina: cartilage at bifurcation. Membrane of carina especially sensitive to irritation and inhaled objects initiate the cough reflex – Primary bronchi divide into secondary bronchi (one/lobe) which then divide into tertiary bronchi. – Tertiary bronchi further subdivide into smaller and smaller bronchi then into bronchioles (less than 1 mm in diameter), then finally into terminal bronchioles. 23-11  Tracheobronchial Tree Larynx Air passageway decrease in siz Trachea Carina but increase in number. Visceral pleura Parietal pleura Pleural cavity Main (primary) bronchus Main (primary) bronchus Lobar (secondary) Lobar (secondary) bronchus bronchus Segmental (tertiary) bronchu Segmental (tertiary) bronchus Bronchiole Bronchiole To terminal To terminal bronchiole bronchiole ( Diaphragm Anterior view (a)  Respiratory Zone: Respiratory Bronchioles to Alveoli Respiratory zone: site for gas exchange – Respiratory bronchioles branch from terminal Terminal bronchiole bronchioles. Respiratory bronchioles Alveolus – Respiratory Alveolar ducts bronchioles have Alveoli Alveolar sac very few alveoli. Give rise to alveolar Visceral pleura Pulmonary capillaries Pleural cavity ducts which have Parietal pleura more alveoli. (a) – Alveolar ducts end as alveolar sacs that have 2 or 3 alveoli at their terminus. 23-13  Alveolar Structure 300 million alveoli in the two lungs. Two types of cells form alveolar wall: – Type I pneumocytes. Thin squamous epithelial cells, form 90% of surface of alveolus. Gas exchange. – Type II pneumocytes. Round or cube-shaped secretory cells. Produce surfactant that makes it easier for the alveoli to expand during inspiration. 14  The Respiratory Membrane Respiratory membrane: location of pulmonary gas exchange. – Oxygen enters blood, carbon dioxide exits blood. Membrane is very thin; composed of alveolar cell layer, capillary endothelial layer, and interstitial space. Layers of the respiratory membrane. 1. Thin layer of fluid lining the alveolus. 2. Alveolar epithelium (simple squamous epithelium. 3. Basement membrane of the alveolar epithelium. 4. Thin interstitial space. 5. Basement membrane of the capillary endothelium. 6. Capillary endothelium composed of simple squamous epithelium. 15 Alveolus and the Respiratory Membrane Type II pneumocyte Alveolar Macrophage (surfactant- epithelium (wall) Air space within secreting cell) alveolus Type I Nucleus pneumocyte Mitochondrion Pulmonary capillary endothelium (wall) Red blood cell (c) Alveolus Alveolar fluid Diffusion (with surfactant) of O2 Alveolar epithelium Capillary endothelium Respiratory Fused basement membrane membrance of the alveolar epithelium and the capillary endothelium Red blood cell Diffusion of CO2 Capillary (d) 16 Lungs: Principal organs of respiration Base sits on diaphragm Apex is at the top, Hilum on medial surface where bronchi and blood vessels enter the lung. – All the structures in hilus called root of the lung. Right lung: three lobes. Lobes separated by fissures Left lung: Two lobes, and an indentation called the cardiac notch – Divisions Lobes (supplied by secondary bronchi), bronchopulmonary segments (supplied by tertiary bronchi and separated from one another by connective tissue partitions), Lobules (supplied by bronchioles and separated by incomplete partitions). 23-17  Anatomy of the Lungs Superior lobe Pulmonary arteries Hilum Hilum Horizontal fissure Primary bronchi Pulmonary Cardiac impression Middle lobe veins Cardiac notch Oblique fissure Inferior lobe Oblique fissure Right lung Left lung (a) Medial views Apex Apex Apico- Broncho- Apical posterior pulmonary Anterior Broncho- Posterior segments of Superior pulmonary superior lobe Anterior lingular segments of Inferior superior lobe Broncho- lingular Medial pulmonary Superior segments of Lateral middle lobe Superior Lateral Broncho- Posterior basal pulmonary Broncho- basal segments of pulmonary Lateral Posterior segments of basal inferior lobe basal inferior lobe Anterior Anterior basal basal Base Base 23-18 Right lung, lateral view Left lung, lateral view (b)  Pleura Visceral pleura: adherent to lung. Simple squamous epithelium, serous. Parietal pleura: adherent to internal thoracic wall. Pleural cavity surrounds each lung and is formed by the pleural membranes. Filled with pleural fluid. – Pleural fluid: acts as a lubricant and helps hold the two membranes close together (adhesion). 23-19  Pleura Parietal pleura Visceral pleura Pleural cavity containing pleural fluid Lung Diaphragm (a) Vertebra Ribs Esophagus (in posterior Right lung mediastinum) Left lung Right main bronchus Parietal pleura Root of lung Right pulmonary Pleural cavity artery at hilum Right pulmonary Visceral pleura vein Fibrous pericardium Pulmonary trunk Parietal pericardium Heart Pericardial cavity Visceral pericardium Sternum Anterior mediastinum (b) Superior view  23.3 Pulmonary Ventilation Movement of air into and out of lungs Air moves from area of higher pressure to area of lower pressure – Boyle’s Law: P = k/V, where P = gas pressure, V = volume, k = constant at a given temperature. – As volume of a container increases (such as the thoracic cavity during inspiration), pressure inside decreases, and vice versa (inverse proportion). 23-21  Atmospheric pressure = 760 mm Hg Atmospheric pressure = 760 mm Hg End of expiration During inspiration No air Air moves in. movement Ribs Intra-alveolar pressure Intra-alveolar pressure equals atmospheric is less than atmospheric pressure. pressure. Diaphragm (760 mm Hg) Diaphragm (759 mm Hg) contracts. Thorax expands and Intra-alveolar thoracic volume increases. Pressure Changes 1 At the end of expiration, alveolar pressure is 2 During inspiration, increased thoracic equal to atmospheric pressure, and there is volume results in increased alveolar volume no air movement. and decreased alveolar pressure. Atmospheric pressure is greater than alveolar pressure, and air moves into the Atmospheric pressure = 760 mm Hg lungs.Atmospheric pressure = 760 mm Hg End of inspiration During expiration No air Air moves out. movement Intra-alveolar pressure Intra-alveolar pressure equals atmospheric is greater than atmospheric pressure. pressure. (760 mm Hg) Diaphragm (761 mm Hg) relaxes. Thorax recoils and thoracic volume decreases. During expiration, decreased thoracic 3 At the end of inspiration, alveolar pressure is 4 volume results in decreased alveolar equal to atmospheric pressure, and there is no volume and increased alveolar pressure. air movement. Alveolar pressure is greater than atmospheric pressure, and air moves out of the lungs. 23.4 Measurement of Lung Function Inspiration: Inhaling = Breathing in Expiration: Exhaling = Breathing out Spirometry: measures volumes of air that move into and out of respiratory system. Uses a spirometer Tidal volume: amount of air inspired or expired with each breath. At rest: 500 mL Inspiratory reserve volume: amount that can be inspired forcefully after inspiration of the tidal volume (3000 mL at rest) Expiratory reserve volume: amount that can be forcefully expired after expiration of the tidal volume (100 mL at rest) Residual volume: volume still remaining in respiratory passages and lungs after most forceful expiration (1200 mL) 23-23  Volume (mL) 0 1000 2000 3000 4000 5000 6000 Time Maximum expiration Maximum inspiration Expiratory Tidal Residual reserve Lung Volumes volume Inspiratory reserve volume volume volume (500 (3000 mL) (1200 mL) (1100 mL) mL) Volumes 23-24  Pulmonary (LUNG) Capacities Pulmonary Capacities The sum of two or more pulmonary volumes Inspiratory capacity: tidal volume plus inspiratory reserve volume Functional residual capacity: expiratory reserve volume plus residual volume Vital capacity: sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume Total lung capacity: sum of inspiratory and expiratory reserve volumes plus tidal volume and residual volume. 23-25  Volume (mL) 0 1000 2000 3000 4000 5000 6000 Time Maximum expiration Maximum inspiration Expiratory Tidal Residual reserve volume Inspiratory reserve volume volume volume (500 (3000 mL) (1200 mL) (1100 mL) mL) Volumes Functional residual capacity (2300 mL) Inspiratory capacity (3500 mL) Vital capacity (4600 mL) Capacities Lung Volumes and Lung Capacities Total lung capacity (5800 mL) 23-26 Average Values Lung Volumes and Lung Capacities Volume/Capacity Abbreviation Average Value (young adult male) Tidal Volume TV 500 mL Expiratory Reserve Volume ERV 1100 mL Residual Volume RV 1200 mL Inspiratory Reserve Volume IRV 3000 mL Inspiratory Capacity (IRV + TV) IC 3500 mL Vital Capacity (IRV + TV + ERV) VC 4600 mL Functional Residual Capacity (ERV + RV) FRC 2300 mL Total Lung Capacity (IRV + TV + ERV + RV) TLC 5800 mL 23-27  Minute Ventilation and Alveolar Ventilation Minute ventilation: total air moved into and out of respiratory system each minute; tidal volume X respiratory rate Respiratory rate (respiratory frequency): number of breaths taken per minute Anatomic dead space: formed by nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles Physiological dead space: anatomic dead space plus the volume of any alveoli in which gas exchange is less than normal. Alveolar ventilation (VA): volume of air available for gas exchange/minute – VA=(tidal volume − dead space) × 23-28 respiratory rate  Functions of the Respiratory System Respiration: inspiration, expiration, gas exchange Regulation of blood pH: Altered by changing blood carbon dioxide levels. Production of chemical mediators: ACE, an enzyme involved in blood pressure regulation. Voice production: Movement of air past vocal folds makes sound and speech. Olfaction: Smell occurs when airborne molecules are drawn into nasal cavity. Protection: Against microorganisms by preventing entry and removing them from respiratory surfaces. 29  Respiration Pulmonary ventilation (breathing): movement of air into and out of lungs. Inspiration – breathing in Expiration – breathing out Gas exchange (Pulmonary gas exchange): diffusion of gases across plasma membranes; two types of Pulmonary gas exchange: – Pulmonary gas exchange (External): gas exchange between air in lungs and blood. – Tissue gas exchange (Internal): gas exchange between the blood and tissues. 30  Respiration Pulmonary ventilation and gas exchange occur in different locations: Upper respiratory tract: structures from nose to larynx. Lower respiratory tract: structures from trachea through alveoli. Upper and lower respiratory tracts further divided: Conducting zone: nose → small air tubes in lungs strictly for pulmonary ventilation Respiratory zone: specialized, small tubes and alveoli where gas exchange occurs. 31  Tracheobronchial Tree Tracheobronchial tree: trachea and network of air tubes in lungs. Trachea to terminal bronchioles is ciliated for removal of debris. Cartilage: holds tube system open Smooth muscle: controls tube diameter As tubes become smaller, amount of cartilage decreases, amount of smooth muscle increases. 32  Tracheobronchial Tree Classes of passages (larges to smallest): Lobar (secondary) bronchi: arise from main bronchi; each serves a lobe of the lungs; contain cartilage plates and are lined with pseudostratified ciliated columnar epithelium. Three on the right and two on the left. Segmental (tertiary) bronchi: supply bronchopulmonary segments. Bronchioles: less than 1 mm in diameter; larger bronchioles lined with ciliated simple columnar epithelium. Terminal bronchioles: no cartilage in walls, but prominent smooth muscle; lined with ciliated simple cuboidal epithelium. Respiratory bronchioles branch from terminal bronchioles Respiratory bronchioles have very few alveoli. 33 acheobronchial Tree 34  Alveoli Alveoli: sites of pulmonary gas exchange. – Open-up from alveolar ducts which branch from respiratory bronchioles – Alveolar sacs are chambers connected to two or more alveoli at the end of an alveolar duct. In alveoli: no cilia, but debris removed by macrophages. – Macrophages then move into nearby lymphatics or into terminal bronchioles. 35 Bronchioles and Alveoli 36  Alveolar Structure 300 million alveoli in the two lungs. Two types of cells form alveolar wall: – Type I pneumocytes. Thin squamous epithelial cells, form 90% of surface of alveolus. Gas exchange. – Type II pneumocytes. Round or cube-shaped secretory cells. Produce surfactant. – Surfactant makes it easier for the alveoli to expand during inspiration. 37  Alveoli Contain The Respiratory Membrane Respiratory membrane: location of pulmonary gas exchange. – Oxygen enters blood, carbon dioxide exits blood. Membrane is very thin Composed of: – alveolar cell layer – capillary endothelial layer – interstitial space 38  Layers of the Respiratory Membrane 1.Thin layer of fluid lining the alveolus. 2.Alveolar epithelium (simple squamous epithelium. 3.Basement membrane of the alveolar epithelium. 4.Thin interstitial space. 5.Basement membrane of the capillary endothelium. 6.Capillary endothelium composed of simple squamous epithelium. 39  Thoracic cavity Space enclosed by thoracic wall and diaphragm Thoracic wall: Consists of thoracic vertebrae, ribs, costal cartilages, sternum and associated muscles Diaphragm separates thoracic cavity from abdominal cavity Muscles change cavity size during pulmonary ventilation. Diaphragm 23-40  Muscles of Inspiration Quiet Inspiration – active process Diaphragm contracts and flattens downward. External intercostals contract and raise the ribs and sternum. Forced Inspiration – labored breathing The pectoralis minor and scalenes contract to raise the ribs and sternum more to give a greater increase of thoracic volume. 41 Inspiration: Changes in Thoracic Volume Access the text alternative for slide images. 42  Muscles of Expiration Quiet Expiration – passive process Diaphragm relaxes and raises External intercostals relax and ribs rebound down. Forced Expiration - active process, labored breathing Abdominal muscles contract and push the diaphragm up more. Internal intercostals contract to pull the ribs inward to decrease thoracic volume more. 43 Expiration: Changes in Thoracic Volume Access the text alternative for slide images. 44  Pulmonary Ventilation Movement of air into and out of lungs – Inspiration – Expiration Air moves from area of higher pressure to area of lower pressure The relationship between Pressure and Volume: – Boyle’s Law: P = k/V, where P = gas pressure, V = volume, k = constant at a given temperature. – As volume of a container increases (such as the thoracic cavity during inspiration), pressure inside decreases, and vice versa (inverse proportion). 23-45  Physiology of the Respiratory System Barometric air pressure = air pressure outside body. Intra-alveolar pressure = air pressure in alveoli. Alveolar Pulmonary ventilation during quiet resting. – Alveolar pressure equals atmospheric pressure » no air movement. – Alveolar pressure less than atmospheric » due to increase in thoracic volume » air moves into lungs. – Alveolar pressure again equals atmospheric » at the end of inspiration » no air movement. – Alveolar pressure greater than atmospheric » due to decrease in thoracic volume » air moves out of lungs. 46 Intra-alveolar Pressure Changes During Inspiration and Expiration 47 Intra-alveolar Pressure Changes During Inspiration and Expiration 48  Factors Affecting Alveolar Ventilation Lung recoil: tendency for lungs to decrease in size after being stretched; due to elastic recoil and surface tension. – Elastic recoil: elastic fibers in the alveolar walls return to original shape after being stretched. – Surface tension: film of fluid lines the alveoli. Where water interfaces with air, polar water molecules have great attraction for each other (hydrogen bonds) with a net pull in toward other water molecules. Tends to make alveoli collapse. – Surfactant: prevents tendency of lungs to collapse by reducing surface tension. Produced by type II pneumocytes. » Infant respiratory distress syndrome – common in premature babies because of inadequate surfactant. 49  Factors Affecting Alveolar Ventilation Pleural pressure: pressure within pleural cavity (between parietal and visceral pleura). – Negative pressure causes lungs to expand during inspiration; pulls the lung outward like suction. Alveoli expand when pleural pressure is low enough to overcome lung recoil. – Pneumothorax is an opening between pleural cavity and air that causes a loss of pleural pressure and the lungs collapse. 50 Dynamics of a Normal Breathing Cycle 51  Hering-Breuer Reflex Limits the degree of inspiration and prevents over-inflation of the lungs – Infants Reflex plays a role in regulating basic rhythm of breathing and preventing over-inflation of lungs – Adults Reflex important only when tidal volume large as in exercise 23-52  Compliance Measure of the ease with which lungs and thorax expand – The greater the compliance, the easier it is for a change in pressure to cause expansion – A lower-than-normal compliance means the lungs and thorax are harder to expand Conditions that decrease compliance – Pulmonary fibrosis: deposition of inelastic fibers in lung (emphysema) – Pulmonary edema – Respiratory distress syndrome – Increased resistance to airflow caused by airway obstruction (asthma, bronchitis, lung cancer) – Deformities of the thoracic wall (kyphosis, scoliosis) 23-53  Alveoli Contain The Respiratory Membrane Respiratory membrane: location of pulmonary gas exchange. – Oxygen enters blood, carbon dioxide exits blood. Membrane is very thin Composed of: – alveolar cell layer – capillary endothelial layer – interstitial space 54  Factors Affecting Diffusion Through the Respiratory Membrane 1. Partial pressure gradients: Gas moves from area of higher partial pressure to area of lower partial pressure. Normally, partial pressure of oxygen is higher in alveoli than in blood. Opposite is usually true for carbon dioxide. 2. Membrane thickness. The thicker the respiratory membrane, the lower the diffusion rate. Diseases like tuberculosis or pneumonia can increase membrane thickness as inflammatory fluid accumulates. 3. Surface area: Decreased surface area decreases diffusion rate. Diseases like emphysema and lung cancer reduce available surface area. 55 Gas Exchange 56  Behavior of Gases and Gas Exchange Partial pressure: The pressure exerted by each type of gas in a mixture. – Dalton’s law: total pressure is the sum of the individual pressures of each gas. The sum of the pressure for nitrogen + oxygen + carbon dioxide + water vapor = atmospheric pressure. 57  Behavior of Gases and Gas Exchange Diffusion of gases into and out of liquids – Henry’s law: Concentration of a gas in a liquid is determined by its partial pressure and its solubility coefficient at a given temperature – Solubility coefficient: measure of how soluble a gas is in a liquid 58  Diffusion Coefficient Diffusion coefficient: rate at which gas diffuses into an out of a liquid or tissue – Factors involved = solubility coefficient and molecular weight of the gas – For example, the diffusion coefficient for O2 is 1 and the relative diffusion coefficient for CO2 is 20 which means CO2 diffuses about 20 times more readily than O2 does – The diffusion coefficient for CO2 is 20:1 59  23.6 Oxygen and Carbon Dioxide Transport in the Blood Oxygen Carbon dioxide – Moves from alveoli into – Moves from blood. – Blood is almost tissues into tissue completely saturated capillaries with oxygen when it – Moves from leaves the capillary pulmonary – Oxygen moves from tissue capillaries into capillaries into the the tissues alveoli 23-60 Gas Exchange 61  Gas Exchange: Oxygen 1. The PO2 of alveolar air averages approximately 104 mm Hg. The P O2 in the pulmonary capillaries is approximately 40 mm Hg. Thus, because the PO is higher in the alveolar air, O2 diffuses into the pulmonary 2 capillaries, down its partial pressure gradient 62  Gas Exchange: Oxygen 2. Even if a person is exercising, by the time blood reaches the venous ends of the pulmonary capillaries, an equilibrium has been achieved and the PO in the blood is 104 mm Hg 2 63  Gas Exchange: Oxygen 3. There is a slight decrease in the PO2 of blood in the pulmonary veins to about 95 mm Hg. This slight decrease is due to mixing of deoxygenated blood from the bronchial veins with blood leaving the pulmonary capillaries. 64  Gas Exchange: Oxygen 4. The PO2 of arterial blood as it arrives in the tissues is still 95 mm Hg compared to the PO of the interstitial fluid, which is 40 mm Hg. The PO in 2 2 individual tissue cells is around 20 mm Hg. Thus, O2 diffuses out of the capillaries into the interstitial fluid and across the plasma membrane of individual cells. The individual cells then use the O2 to 65  Gas Exchange: Oxygen 5. By the time blood has reached the venous end of a capillary network, it has achieved an equilibrium with the cells and interstitial fluid. 66  Gas Exchange: Carbon Dioxide As cells produce CO2, the intracellular PCO increases to approximately 46 mm Hg 2 and the interstitial fluid PCO2 is approximately 45 mm Hg (see step 5). The PCO2 of arterial blood as it arrives in the tissues is 40 mm Hg. Thus, CO2 diffuses out of the cells, into the interstitial fluid and into the blood, down its partial pressure gradient. By the time blood has reached the venous end of the capillary network, it has achieved an equilibrium with the interstitial fluid and has a P of 45 mm Hg. 67  Gas Exchange: Carbon Dioxide The PCO of the blood when it returns to the arterial end of the pulmonary capillaries is 2 still 45 mm Hg compared to a PCO2 of 40 mm Hg in the alveoli (see steps 1 and 2). Thus, at the alveoli, CO2 diffuses out of the blood down its partial pressure gradient. At the venous end of the pulmonary capillaries,PCO has achieved an 2 equilibrium with the alveoli and has decreased to 40 mm Hg. 68 Gas Exchange 69  23.6 Oxygen and Carbon Dioxide Transport in the Blood Hemoglobin: – Protein synthesized by immature red blood cells; occupies much of red blood cell volume. – Four types: embryonic, fetal, adult, and hemoglobin-S (in those with sickle-cell disease). – Embryonic and fetal hemoglobin have a higher concentration of hemoglobin and a greater affinity for O2 than maternal hemoglobin. – Adult has 4 subunits, each containing one iron- based heme group, so 1 hemoglobin can carry up to 4 O2. 70  Hemoglobin and Oxygen Transport – About 98.5% of O2 transport is by hemoglobin. – About 1.5% is dissolved in plasma. Oxygen-hemoglobin dissociation curve describes the percent saturation of hemoglobin at different PO values. 2 – At PO of 104 mm Hg, hemoglobin is 98% saturated. 2 – At PO of 60 mm Hg, hemoglobin is 90% saturated. 2 – At PO of 40 mm Hg (such as at the tissues), PO is 40 mm Hg and 2 2 so blood leaving tissues is still 75% saturated. Used as a reserve if blood PO levels decrease further, as during 2 exercise. 23-71 Oxygen-Hemoglobin Dissociation Curve Access the text alternative for slide images. 72  Bohr Effect Effect of pH on oxygen-hemoglobin dissociation curve – as pH of blood decreases, amount of oxygen bound to hemoglobin at any given PO2 also declines Occurs because decreased pH yields increase in H+ that combines with hemoglobin changing its shape so oxygen cannot bind to hemoglobin 23-73 Shifting the Oxygen-Hemoglobin Dissociation Curve 74  Effects of CO2 and Temperature Increase in PCO2 causes decrease in pH Increase temperature: decreases tendency for oxygen to remain bound to hemoglobin – as metabolism goes up, more oxygen is released to the tissues. 23-75  Effect of BPG 2,3-bisphosphoglycerate (BPG): released by RBCs as they break down glucose for energy Binds to hemoglobin and increases release of oxygen 23-76  Fetal Hemoglobin Fetal hemoglobin picks up oxygen from maternal hemoglobin Concentration of fetal hemoglobin is 50% greater than concentration of maternal hemoglobin. Fetal hemoglobin can bind oxygen better than maternal BPG has little effect on fetal hemoglobin. – Does not cause it to release oxygen 23-77  Transport of Carbon Dioxide About 7% dissolves in the plasma About 23% binds to the globin of hemoglobin Haldane Effect - as hemoglobin binds to CO2, its affinity for O2 is reduced. The less O2 that is bound to hemoglobin, the more CO2 can bind and vice versa About 70% is transported as bicarbonate ion dissolved either in the cytoplasm of RBCs or in the plasma of the blood – The enzyme carbonic anhydrase catalyzes the reaction that forms bicarbonate ions – Reaction to form bicarbonate CO2  H2 O  H2 CO3  H  HCO3 - 23-78  Systemic Gas Exchange 1. CO2 enters red blood cells 2. Carbonic anhydrase uses water and CO2 to form bicarbonate and hydrogen ions. 3. Chloride ions enter the RBC and bicarbonate ions leave: chloride shift. 4. Hydrogen ions combine with hemoglobin. -Lowering the concentration of bicarbonate and hydrogen ions inside RBCs promotes the conversion of CO2 to bicarbonate ion. 79  Pulmonary Gas Exchange 1. CO2 leaves red blood cells 2. Additional CO2 is formed from carbonic acid 3. The bicarbonate ions are exchanged for chloride ions 4. The hydrogen ions are released from hemoglobin 80 Gas Exchange 81  Neural Control of Ventilation Regulation of pulmonary ventilation can be under voluntary control as when eating or speaking, yet during sleep or when focused on other tasks, is regulated involuntarily. 82  Respiratory Areas in the Brainstem Medullary respiratory center in the medulla oblongata Ventral respiratory group (VRG) – produces the normal, involuntary rhythm of breathing called eupnea. – Has a collection of neurons active during both inspiration and expiration. – Pre-Bötzinger Complex – part of V G R that establishes the basic rhythm of pulmonary ventilation. Dorsal respiratory group (DRG) – receives input from chemoreceptors and mechanoreceptors and other sources to modify the respiratory rhythm. Pontine respiratory group in the pons – Connects to the medullary respiratory center and appears to play a role in switching between inspiration and expiration. 83  Chemical Control of Ventilation Chemoreceptors: specialized neurons that respond to changes in chemicals in solution – Central chemoreceptors: chemosensitive area of the medulla oblongata; connected to respiratory center – Peripheral chemoreceptors: carotid and aortic bodies. Connected to respiratory center by cranial nerves IX and X Effect of pH: Lower pH triggers increase in rate and depth of breathing, reducing carbon dioxide and raising pH to normal. – Chemosensitive areas respond indirectly through changes in carbon dioxide – Carotid and aortic bodies respond directly to pH changes 23-84  Chemical Control of Ventilation Effect of carbon dioxide: small change in carbon dioxide in blood triggers a large increase in rate and depth of respiration – Hypercapnia: greater-than-normal amount of carbon dioxide, increases breathing rate – Hypocapnia: lower-than-normal amount of carbon dioxide, decreases breathing rate – Chemosensitive area in medulla oblongata is more important for regulation of CO2 and pH – Carotid bodies respond rapidly to changes in blood pH because of exercise 23-85 Regulation of Blood CO2 86  Chemical Control of Ventilation Effect of oxygen: carotid and aortic body chemoreceptors respond to decreased O2 by increased stimulation of respiratory center to keep it active despite decreasing oxygen levels – Hypoxia: decrease in oxygen levels below normal values 23-87 Other Major Regulatory Mechanisms of Pulmonary Ventilation 88  Effect of Exercise on Ventilation Ventilation increases abruptly – At onset of exercise – Movement of limbs has strong influence – Learned component Ventilation increases gradually – After immediate increase, gradual increase occurs (4-6 minutes) – Anaerobic threshold: highest level of exercise without causing significant change in blood pH. If exceeded, lactic acid produced by skeletal muscles 23-89