Respiratory System Lecture Notes
Respiratory System Lecture Notes BMS 251-20
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This 12 page Class Notes was uploaded by Claire Neville on Thursday March 10, 2016. The Class Notes belongs to BMS 251-20 at Grand Valley State University taught by Dr. Tara Alger in Winter 2016. Since its upload, it has received 42 views. For similar materials see Anatomy & Physiology II in Biomedical Sciences at Grand Valley State University.
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Date Created: 03/10/16
Chapter 23 Respiratory System The Respiratory System Respiration is gas exchange: O for CO 2 2 o Occurs between atmosphere and body cells ATP production through aerobic respiration requires oxygen, and Carbon dioxide is a biproduct The respiratory system provides the means for gas exchange o Consists of respiratory passageways in head, neck, and trunk The lungs 23.1a General Functions of the Respiratory System Air passageway o Inspiration: movement of air from atmosphere into the lungs o Expiration: Air moves from lungs to atmosphere Site for oxygen and carbon dioxide exchange o Oxygen diffuses from alveoli into blood o Carbon dioxide diffuses from blood into alveoli Odor detection o Olfactory receptors in superior nasal cavity o Sensory input is relayed to the brain Sound production o Air moves across vocal cords of the larynx (voice box) o Vocal cords vibrate, producing sound o Sounds resonate in the upper respiratory structures Rate and depth of breathing influ+nce o Blood levels of O ,2CO ,2H o Venous return of blood; lymphatic return of fluid to blood 23.1b General Organization of the Respiratory System Structural organization o Upper respiratory tract Larynx and above o Lower respiratory tract Trachea and below Functional organization o The conducting zone transports air Nose to terminal bronchioles o The respiratory zone participates in gas exchange Respiratory bronchioles to alveoli 23.1c Respiratory Mucosa Mucosa = mucous membrane: respiratory lining o Epithelium resting on a basement membrane o Lamina Propria: Connective tissue layer beneath Respiratory epithelium o Becomes thinner from the nose to the alveoli pseudostratified ciliated columnar simple ciliated columnar simple cuboidal simple squamous Mucous secretions o Produced from secretions of Goblet cells of epithelial lining Mucous and serous glands of the lamina propria o Contain mucin protein Increases mucus viscosity and serves to trap dust, dirt, pollen, etc. o Contains defenses against microbes Lysozyme (antibacterial enzyme) Defensins (antibacterial proteins) Immunoglobulin A (antibody) 23.2a Nose and Nasal Cavity Nose: external structure including bone, cartilage and skin Choanae: o Floor formed by palate o Nasal septum divides left and right sides Posterior part is bony perpendicular plate of ethmoid plate and vomer bone The Nasal Cavity o Three paired, bony projections on lateral walls of nasal cavity Superior, middle, and inferior conchae o Produce turbulence in inhaled air o Partition the nasal cavity into separate passages Each passage called a Nasal meatus Nasal cavity parts o Nasal vestibule: just inside nostrils Lined by skin and particle-trapping hairs (vibrissae) o Olfactory region Superior part of nasal cavity containing olfactory epithelium Airborne molecules stimulate receptors for odor detection o Respiratory region Lined by pseudostratified ciliated columnar epithelium Has an extensive vascular network Nosebleeds common due to large numbers of superficial vessels Nasal cavity warms, cleanses, and humidifies o Air is warmed by extensive blood vessels o Mucus traps dust, microbes, and foreign material o Cilia sweep mucous toward the pharynx to be swallowed o Moist environment humidifies o Air turbulence created by conchae enhances all three processes 23.2b Paranasal Sinuses Paranasal Sinuses: spaces within skull bones o Named for specific bone in which they are housed o All connected by ducts to nasal cavity 23.2c Pharynx Pharynx (throat) o Funnel-shaped passageway posterior to nasal cavity, oral cavity, and larynx o Lateral walls composed of skeletal muscles o Partitioned into Nasopharynx Oropharynx Laryngopharynx Nasopharynx most superior part of pharynx o Posterior to nasal cavity, superior to soft palate o Lined by pseudostratified ciliated columnar epithelium o An air passage—not for food Soft palate elevates during swallowing, blocking food or drink o Connects to middle ear via auditory tubes Opening tubes allows equalization of pressure on each side of tympanic membrane o Contains tonsils—infection-fighting lymphatic tissue 23.3a Larynx Larynx (voice box) o Cylindrical airway between laryngopharynx and trachea o Several functions Air passageway (usually open) Prevents ingested materials from entering respiratory tract epiglottis covers superior opening during swallowing Produces sound for speech Vocal cords (ligaments) vibrate during expiration Participates in sneeze and cough reflexes Abdominal muscles contract increasing thoracic pressure Vocal cords are forcibly opened by pressure from below Explosive blast of exhaled air is a cough or sneeze 23.3a Larynx anatomy Vocal: o Composed primarily of elastic connective tissue o Covered with mucosa to form the vocal folds (true vocal cords) o Produce sound when air passes between them o rima glottides: space between the vocal ligaments Vestibular folds: superior to vocal folds o Covered with mucosa to form the vestibular folds (false vocal cords) o Play no role in sound production o Protect vocal cords o Extrinsic skeletal muscles Stabilize larynx and help it move during swallowing o Intrinsic skeletal muscles Located within larynx Contraction results in change in size of rima glottidis Involved in voice production and swallowing Sound production: vocal cord vibration Intrinsic laryngeal muscles narrow opening of rima glottidis Air is forced past vocal cords during expiration o Range of voice determined by length, thickness of vocal cords Males have longer and thicker folds, and so deeper voices o Pitch (frequency) determined by tension on vocal cords Increased tension = folds vibrate more = higher pitch Regulated by intrinsic laryngeal muscles o Loudness depends on force of air passing across vocal cords More air = louder sound o Other structures are also necessary for speech Pharynx, nasal and oral cavities, and paranasal sinuses serve as resonating chambers Lips, teeth, and tongue help form speech sounds 23.3b Trachea Gross anatomy of trachea (windpipe) o Flexible, slightly rigid, tubular organ o Goes from larynx to main bronchi o Tracheal cartilages support anterior and lateral walls C-shaped rings of hyaline cartilages Ensure trachea is always open o Carina: internal ridge at inferior end of trachea (where it splits) containing many sensory receptors Initiates cough reflex when irritants are present o Trachealis muscle on trachea’s posterior surface Connects open ends of C-shaped cartilages Allow accommodation for esophagus when bulge of food passes Trachealis contracts during coughing 23.3c Bronchial Tree Bronchial tree: system of highly branched air passages o Originates at main bronchi, branches to more narrow tubes o Ends in small bronchiole passageways Gross anatomy of bronchial tree o Trachea splits into right and left main bronchi (primary bronchi) at level of sternal angle Each bronchus enters a lung on its medial surface Right bronchus shorter, wider, and more vertically oriented Foreign particles more likely to lodge here o Each main bronchus branches into smaller tubes, from primary to secondary, to tertiary bronchi o Eventually leading to bronchioles o Tree continues to divide into smaller passageways Leads to terminal bronchioles (last part of conducting zone) Leads to respiratory bronchioles (first part of respiratory zone) o Bronchioles have no cartilage Have proportionally thicker layer of smooth muscle Muscle contraction narrows bronchiole diameter bronchoconstriction = less air through bronchial tree (less entry of potentially harmful substances) Muscle relaxation increases bronchiole diameter bronchodilation = more air through the bronchial tree 23.3d Respiratory Zone: Respiratory Bronchioles, Alveolar Ducts, and Alveoli Respiratory zone structures are microscopic o Respiratory bronchioles subdivide to alveolar ducts o Alveolar ducts lead to alveolar sacs, clusters of alveoli o Alveoli = spherical organization of squamous cells Epithelium o Respiratory bronchioles lined with simple cuboidal epithelium o Alveoli and alveolar ducts lined by simple squamous o Thinness facilitates gas exchange Cell types of alveolar wall o Simple squamous alveolar type I cells 95% of alveolar surface area Part of thin barrier separating air from blood o Alveolar type II ceIIs Secrete oily pulmonary surfactant Coats inside of alveolus and opposes collapse during expiration o Alveolar macrophages (dust cells) Leukocytes that engulf microorganisms Either fixed in alveolar wall or free to migrate 23.3e Respiratory Membrane The respiratory membrane o Thin barrier between alveoli and pulmonary capillaries o Consists of Alveolar epithelium and its basement membrane Capillary epithelium and its basement membrane o Oxygen diffuses from alveolus into capillaries Erythrocytes become oxygenated o Carbon dioxide diffuses from blood to alveolus Expired to external environment 23.4a Gross Anatomy of the Lung Lungs are in thorax on either side of mediastinum o House bronchial tree and all respiratory portions of respiratory system hilum o Indented region on lung’s mediastinal side o Bronchi, pulmonary vessels, autonomic nerves, lymph vessels pass through here These structures collectively termed the root of the lung Right lung is larger and wider than left lung o Has three lobes divided by two fissures Left lung is smaller than right due to heart’s position o Has two lobes divided by one fissure o surface indentations accommodate heart and aorta Cardiac impression on medial surface Cardiac notch on anterior surface 23.4b Circulation to and Innervation of the Lungs Blood supply Two types of circulation in the lungs o Pulmonary circulation o Bronchial circulation Pulmonary circulation replenishes O , eli2inates CO 2 o Pulmonary arteries carry deoxygenated blood to pulmonary capillaries o Blood is reoxygenated o Blood enters pulmonary venules and veins, returns to left atrium Bronchial ciruclation transports oxygenated blood to tissues of lungs o Bronchial arteries branch off descending aorta o Bronchial veins collect venous blood Lymph drainage o Lymph vessels and nodes located: Within lung’s connective tissue Around bronchi In pleura o Important in removing excess fluid from the lungs Innervation of the respiratory system o Autonomic nervous system innervates smooth muscles and glands of respiratory structures Sympathetic input generally causes bronchodilation Parasympathetic causes bronchoconstriction Sends signals to larynx 23.4c Pleura Membranes and Pleural Cavity Pleura: serous membrane o Outer lining of lung surfaces and adjacent thoracic wall o Composed of simple squamous epithelium o Visceral pleura adheres to lung surface o Parietal Pleura lines Internal thoracic walls Lateral surface of mediastinum Superior surface of diaphragm Pleural Cavity o Located between visceral and parietal serous membranes o When lungs are inflated, considered a potential space Visceral and parietal layers almost touching Serous fluid produced by serous membranes o Covers pleural cavity surface o Lubricates, allowing pleural surfaces to slide by easily 23.4d How Lungs Remain Inflated Intrapleural pressure (between membranes) is low o Chest wall configured to expand outward Lungs cling to chest wall due to serous fluid’s surface tension Because intrapulmonary pressure (in alveoli) is greater than intrapleural pressure, lungs remain inflated Processes of Respiration Respiration (exchange of gases between atmosphere and body’s cells) involves four processes o Pulmonary ventilation: movement of gases between atmosphere and alveoli o Alveolar gas exchange: external respiration): exchange of gases between alveoli and blood o Gas transport: transport of gases in blood between lungs and systemic cells o Systemic gas exchange: internal respiration): exchange of respiratory gases between the blood and the systemic cells 23.5a Introduction to Pulmonary Ventilation Pulmonary ventilation (breathing): air movement o Consists of two cyclic phases Inspiration brings air into the lungs (inhalation) Expiration forces air out of the lungs (exhalation) o Quiet, rhythmic breathing occurs at rest o Forced, vigorous breathing accompanies exercise o Volume changes result in changes in pressure gradient between lungs and atmosphere o Air moves down its pressure gradient 23.5b Mechanics of Breathing Volume changes in the thoracic cavity o Thoracic volume changes vertically, laterally, and anterior-posteriorly o Vertical changes result from diaphragm movement Flattens (by moving inferiorly) when contracted When relaxed, returns to original position, vertical dimensions decrease Boyle’s gas law Relationship of volume and pressure o At constant temperature, pressure (P) of a gas decreases if volume (V) of the container increases, and vice versa o Inverse relationship between gas pressure and volume An air pressure gradient exists when force per unit area is greater in one place than another o If the two places are interconnected, air flows from high to low pressure until pressure is equal Volumes and pressures associated with breathing Atmospheric pressure: pressure of air in environment o Changes with altitude Increased altitude = “thinner air” = lower pressure Sea level value is 760 mm Hg Unchanged in process of breathing Alveolar volume: collective volume of alveoli Intrapulmonary pressure: pressure in alveoli o Fluctuates with breathing Volume changes create pressure changes and air flows down its pressure gradient o During inspiration: thoracic volume increases, thoracic pressure decreases, so air flows in o During expiration: thoracic volume decreases, thoracic pressure increases, so air flows out Forced breathing o Involves steps similar to quiet breathing o Requires contraction of additional muscles o Causes greater changes in thoracic cavity volume and intrapulmonary pressure o More air moves into and out of lungs o Significant chest volume changes are apparent 23.5c Nervous Control of Breathing Autonomic nuclei within the brain coordinate breathing o Respiratory center of the brainstem Medullary respiratory center contains two groups Pontine respiratory center in pons Brainstem neurons influence respiratory muscles + Chemoreceptors monitor changes in concentrations of H , PCO and PO 2 2 o Central chemoreceptors in medulla monitor pH of CSF CSF pH changes are caused by changes in blood PCO 2 carbonic acid is built from CO a2d water o Peripheral chemoreceptors are in aortic and carotid bodies Stimulated by changes in H or respiratory gases in blood Aortic and carotid bodies send signals to respiratory center Other receptors also influence respiration o Proprioceptors of muscles and joints are stimulated by body movements o Baroreceptors in pleurae and bronchioles respond to stretch o Irritant receptors in air passageways stimulated by particulate matter Physiology of quiet breathing o Inspiration begins when medullary group inspiratory neurons fire spontaneously o Signals are sent from VRG to nerve pathways exciting skeletal muscles Diaphragm and external intercostals contract causing air to flow in o Quiet expiration occurs when VRG is inhibited Signals from inspiratory neurons are relayed to VRG expiratory neurons Expiratory neurons send inhibitory signals back (negative feedback) o Signals no longer sent to inspiratory muscles (for about 3 sec) Diaphragm and external intercostals relax causing air to flow out o Respiration rate for normal, quiet breathing is eupnea o Pontine respiratory center facilitates smooth transitions between inspiration and expiration Reflexes that alter breathing rate and depth Rate changes by altering amount of time in inspiration and expiration Depth changes by stimulation of accessory muscles o Ventilation increases in response to Central chemoreceptors detecting increase in H concentration of CSF + Peripheral chemoreceptors detecting increase in blood H or PCO 2 o Increased ventilation expels more CO retu2ning conditions to normal o Ventilation decreases if chemoreceptors detect decreases in H or PCO + 2 o Blood PCO is2most important stimulus affecting breathing CO f2uctuations influence sensitive central chemoreceptors CO 2ombines with water to form carbonic acid in CSF CSF lacks protein buffers and so its pH change triggers reflexes Blood PO i2 not a sensitive regulator of breathing When PO dr2ps it causes peripheral chemoreceptors to be more sensitive to blood PCO 2 o Altering breathing through other receptors Joint and muscle proprioceptors are stimulated by body movement Signal respiratory center to increase breathing depth Baroreceptors within visceral pleura and bronchiole smooth muscle Send signals to respiratory center when overstretched shut off inspiration and protect against overinflation Irritant receptors initiate sneezing and coughing Exaggerated intake of breath followed by closure of larynx Abrupt opening of vocal cords and explosive blast of exhaled air o Action of higher brain centers Hypothalamus increases breathing rate if body is warm Limbic system alters breathing rate in response to emotions Frontal lobe of cerebral cortex controls voluntary changes in breathing patterns 23.5d Airflow, Pressure Gradients, and Resistance Airflow: amount of air moving in and out of lungs with each breath o Depends on The pressure gradient established between atmospheric pressure and intrapulmonary pressure The resistance that occurs due to conditions within the airways, lungs, and chest wall F = ∆P/R o F = flow o ∆P = difference in pressure between atmosphere and intrapulmonary pressure = pressure gradient = P atm– Palv o R = resistance o Flow directly related to pressure gradient and inversely related to resistance If pressure gradient increases, airflow to lungs increases If resistance increases, airflow lessens Resistance: greater difficulty moving air o May be altered by Change in elasticity of chest wall and lungs Change in bronchiole diameter (size of air passageway) Collapse of alveoli o Decreases in chest wall elasticity increase resistance Chest wall elasticity decreases with aging and disease Vertebral malformations (scoliosis) can decrease elasticity Arthritis in thoracic cage Replacement of elastic tissue with scar tissue o Bronchiole diameter varies inversely with resistance Bronchoconstriction or occlusion increase resistance Constriction caused by parasympathetic activity or cold Occlusion by excess mucus or inflammation Bronchodilation decreases resistance Caused by sympathetic stimulation, epinephrine o Collapsed alveoli increase resistance Can occur if alveolar type II cells are not producing surfactant (high surface tension of alveoli is not overcome) An important factor for premature infants ___________________ o Ease with which lungs and chest wall expand o Determined by surface tension and elasticity of chest and lung o The easier the lung expands, the greater the compliance Several conditions can increase resistance to airflow o Decreases in size of bronchiole lumen (asthma) o Decrease in compliance (pulmonary fibrosis) o The result is a need for more forceful inspirations o More forceful inspirations of respiratory disorders require high amount of energy Can cause four-fold to six-fold increase in energy need 23.5e Pulmonary and Alveolar Ventilation Pulmonary ventilation o Process of moving air into and out of the lungs o Amount of air moved between atmosphere and alveoli in 1 minute Tidal volume = amount of air per breath Respiration rate = number of breaths per minute Tidal volume × Respiration rate = Pulmonary ventilation 500 mL × 12 breaths/min = 6 L/ minute (typical amount) 23.6a Chemical Principles of Gas Exchange Partial pressure and Dalton’s law __________________ : pressure exerted by each gas within a mixture of gases, measured in mm Hg o Written with P followed by gas symbol (i.e., PO ) 2 o Each gas moves independently down its partial pressure gradient during gas exchange Atmospheric pressure = 760 mm Hg at sea level o Total pressure all gases collectively exert in the environment o Includes N ,2O ,2CO ,2H O2 and other minor gases Total pressure × % of gas = Partial pressure of that gas o Nitrogen is 78.6% of the gas in air o 760 mm HG × 78.6% = 597 mm Hg = partial pressure of nitrogen Partial pressure __________________ Gradient exists when partial pressure for a gas is higher in one region of the respiratory system than another Gas moves from region of higher partial pressure to region of lower partial pressure until pressures become equal o In lungs: O2 moves from alveoli to the blood CO2 moves from blood to alveoli o In body tissues: O2 moves from blood to tissue CO2 moves from tissue to blood Gas solubility and Henry’s law Henry’s Law at a given temperature, the solubility of a gas in liquid is dependent upon the o Partial pressure of the gas in the air o Solubility coefficient of the gas in the liquid (a constant) volume of gas that dissolves in a specified volume of liquid at a given temperature and pressure Gases vary in their solubility in water o Carbon dioxide about 24 times as soluble as oxygen o Nitrogen about half as soluble as oxygen It does not normally dissolve in blood in significant amounts o Gases with low solubility require larger pressure gradients to “push” the gas into the liquid 23.6b Alveolar Gas Exchange (External Respiration) Efficiency of gas exchange at respiratory membrane Anatomical features of membrane contributing to efficiency o Large surface area o Minimal thickness Physiologic adjustments: ventilation-perfusion coupling o Ability of bronchioles to regulate airflow and arterioles to regulate blood flow Ventilation changes by bronchodilation or bronchoconstriction _______________ changes by pulmonary arteriole dilation or constriction 23.6c Systemic Gas Exchange (Internal Respiration) Oxygen diffuses out of systemic capillaries to enter systemic cells o Partial pressure gradient drives the process PO 2n systemic cells 40 mm Hg PO 2n systemic capillaries is 95 mm Hg o Continues until blood PO is 20 mm Hg o Systemic cell PO st2ys fairly constant Oxygen delivered at same rate it is used unless engaging in strenuous activity Carbon dioxide o Diffuses from systemic cells to blood o Partial pressure gradient driving process PCO in systemic cells 45mm Hg 2 PCO i2 systemic capillaries 40 mm Hg o Diffusion continuing until blood PCO is 25 mm Hg 23.7a Oxygen Transport Blood’s ability to transport oxygen depends on o Solubility coefficient of oxygen This is very low, and so very little oxygen dissolves in plasma o Presence of hemoglobin The iron of hemoglobin attaches oxygen About 98% of O in2blood is bound to hemoglobin HbO is oxyhemoglobin (with oxygen bound) 2 Hb is deoxyhemoglobin (without bound oxygen) 23.7b Carbon Dioxide Transport Carbon dioxide has three means of transport o As CO di2solved in plasma (7%) o As CO at2ached to amine group of globin portion of hemoglobin (23%) HbCO i2 carbaminohemoglobin o As bicarbonate dissolved in plasma (70%) 23.7c Hemoglobin as a Transport Molecule Binding of one substance causes a change in shape of the hemoglobin molecule o Influences the ability of hemoglobin to bind or release the other two substances o Saturation increases as PO inc2eases __________________________: each O th2t binds causes a change in hemoglobin making it easier for next O to 2ind 23.8a Effects of Hyperventilation and Hypoventilation on Cardiovascular Function __________________: breathing rate or depth above body’s demand o Caused by anxiety, ascending to high altitude, or voluntarily o PO r2ses and PCO fall2in the air of alveoli o Additional oxygen does not enter blood because hemoglobin is already saturated o There is greater loss of CO fr2m blood ____________________: breathing too slow or too shallow o Causes include: airway obstruction, pneumonia, brainstem injury, other respiratory conditions o O l2vels down, CO leve2s up in alveoli o Blood PO de2reases and can lead to low oxygen in tissues o Blood PCO increases 2 o Clinical View: Asthma Episodes of bronchoconstriction, wheezing, coughing, shortness of breath, and excess mucus Asthmatic with sensitivity to airborne agent Localized immune reaction occurs in bronchi and bronchioles Walls of the bronchi becoming permanently thickened Clinical View: Measuring Blood Oxygen Levels with a Pulse Oximeter Noninvasive and indirect way to measure oxygen ̶ Applied to finger or earlobe Measure hemoglobin saturation by determining the ratio of oxyhemoglobin to deoxyhemoglobin Normal reading hemoglobin saturation >95%