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This 12 page Class Notes was uploaded by Jess Graff on Monday May 2, 2016. The Class Notes belongs to BMS 508 at University of New Hampshire taught by Mary Katherine Lockwood, PhD in Spring 2016. Since its upload, it has received 6 views. For similar materials see Human Anatomy and Physiology II in Biological Sciences at University of New Hampshire.
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Date Created: 05/02/16
BMS 508.03 3/25/2016 Chapter 23 (cont) Respiration (cont) Pulmonary Ventilation • The Respiratory Cycle • Cyclical changes in intrapleural pressure operate the respiratory pump • Which aids in venous return to heart • Tidal Volume (V ) T • Amount of air moved in and out of lungs in a single respiratory cycle • Injury to the Chest Wall • Pneumothorax allows air into pleural cavity • Atelectasis (also called a collapsed lung) is a result of pneumothorax • The Respiratory Muscles • Most important are: • The diaphragm • External intercostal muscles of the ribs • Accessory respiratory muscles • Activated when respiration increases significantly • The Mechanics of Breathing • Inhalation • Always active • Exhalation • Active or passive • Muscles Used in Inhalation • Diaphragm • Contraction draws air into lungs • 75% of normal air movement • External intercostal muscles • Assist inhalation • 25% of normal air movement • Accessory muscles assist in elevating ribs • Sternocleidomastoid • Serratus anterior • Pectoralis minor • Scalene muscles • Muscles Used in Exhalation • Internal intercostal and transversus thoracis muscles • Depress the ribs • Abdominal muscles • Compress the abdomen • Force diaphragm upward • Modes of Breathing • Respiratory movements are classified • By pattern of muscle activity • Quiet breathing • Forced breathing • Quiet Breathing (Eupnea) • Involves active inhalation and passive exhalation • Diaphragmatic breathing or deep breathing • Is dominated by diaphragm • Costal breathing or shallow breathing • Is dominated by rib cage movements • Elastic Rebound • When inhalation muscles relax • Elastic components of muscles and lungs recoil • Returning lungs and alveoli to original position • Forced Breathing (Hyperpnea) • Involves active inhalation and exhalation • Assisted by accessory muscles • Maximum levels occur in exhaustion • Respiratory Rates and Volumes • Respiratory system adapts to changing oxygen demands by varying: • The number of breaths per minute (respiratory rate) • The volume of air moved per breath (tidal volume) • The Respiratory Minute Volume (V ) E • Amount of air moved per minute • Is calculated by: respiratory rate ´ tidal volume • Measures pulmonary ventilation • Alveolar Ventilation (V ) A • Only a part of respiratory minute volume reaches alveolar exchange surfaces • Volume of air remaining in conducting passages is anatomic dead space • Alveolar ventilation is the amount of air reaching alveoli each minute • Calculated as: (tidal volume anatomic dead space) ´ respiratory rate • Alveolar Gas Content • Alveoli contain less O , more CO than atmospheric air 2 2 • Because air mixes with exhaled air • Relationships among V , V , Tnd E A • Determined by respiratory rate and tidal volume • For a given respiratory rate: • Increasing tidal volume increases alveolar ventilation rate • For a given tidal volume: • Increasing respiratory rate increases alveolar ventilation • Respiratory Performance and Volume Relationships • Total lung volume is divided into a series of volumes and capacities useful in diagnosing problems • Four Pulmonary Volumes • Resting tidal volume (Vt) • Expiratory reserve volume (ERV) • Residual volume • Inspiratory reserve volume (IRV) • Resting Tidal Volume (V ) t • In a normal respiratory cycle • Expiratory Reserve Volume (ERV) • After a normal exhalation • Residual Volume • After maximal exhalation • Minimal volume (in a collapsed lung) • Inspiratory Reserve Volume (IRV) • After a normal inspiration • Four Calculated Respiratory Capacities • Inspiratory capacity • Tidal volume + inspiratory reserve volume • Functional residual capacity (FRC) • Expiratory reserve volume + residual volume • Vital capacity • Expiratory reserve volume + tidal volume + inspiratory reserve volume Total lung capacity • Vital capacity + residual volume • Pulmonary Function Tests • Measure rates and volumes of air movements Gas Exchange • Gas Exchange • Occurs between blood and alveolar air • Across the respiratory membrane • Depends on: • Partial pressures of the gases • Diffusion of molecules between gas and liquid • The Gas Laws • Diffusion occurs in response to concentration gradients • Rate of diffusion depends on physical principles, or gas laws • For example, Boyle’s law • Dalton’s Law and Partial Pressures • Composition of Air • Nitrogen (N ) is about 78.6% 2 • Oxygen (O ) i2 about 20.9% • Water vapor (H O) 2s about 0.5% • Carbon dioxide (CO ) is 2bout 0.04% • Atmospheric pressure (760 mm Hg) • Produced by air molecules bumping into each other • Each gas contributes to the total pressure • In proportion to its number of molecules (Dalton’s law) • Partial Pressure • The pressure contributed by each gas in the atmosphere • All partial pressures together add up to 760 mm Hg • Diffusion between Liquids and Gases • Henry’s Law • When gas under pressure comes in contact with liquid: • Gas dissolves in liquid until equilibrium is reached • At a given temperature: • Amount of a gas in solution is proportional to partial pressure of that gas • The actual amount of a gas in solution (at given partial pressure and temperature): • Depends on the solubility of that gas in that particular liquid • Solubility in Body Fluids • CO 2s very soluble • O2is less soluble • N2has very low solubility • Normal Partial Pressures • In pulmonary vein plasma • P CO2= 40 mm Hg • P O2= 100 mm Hg • P N2= 573 mm Hg • Diffusion and Respiratory Function • Direction and rate of diffusion of gases across the respiratory membrane • Determine different partial pressures and solubilities • Five Reasons for Efficiency of Gas Exchange • Substantial differences in partial pressure across the respiratory membrane • Distances involved in gas exchange are short • O 2nd CO are 2ipid soluble • Total surface area is large • Blood flow and airflow are coordinated • Partial Pressures in Alveolar Air and Alveolar Capillaries • Blood arriving in pulmonary arteries has: • Low P O2 • High P CO2 • The concentration gradient causes: • O 2o enter blood • CO t2 leave blood • Rapid exchange allows blood and alveolar air to reach equilibrium • Partial Pressures in the Systemic Circuit • Oxygenated blood mixes with deoxygenated blood from conducting passageways • Lowers the P O2 of blood entering systemic circuit (drops to about 95 mm Hg) • Interstitial Fluid • P O240 mm Hg • P CO245 mm Hg • Concentration gradient in peripheral capillaries is opposite of lungs • CO d2ffuses into blood • O 2iffuses out of blood Gas Transport • Gas Pickup and Delivery • Blood plasma cannot transport enough O or CO to m2et phys2ological needs • Red Blood Cells (RBCs) • Transport O to2 and CO from,2peripheral tissues • Remove O and 2O from pl2sma, allowing gases to diffuse into blood • Oxygen Transport • O 2inds to iron ions in hemoglobin (Hb) molecules • In a reversible reaction • New molecule is called oxyhemoglobin (HbO ) 2 • Each RBC has about 280 million Hb molecules • Each binds four oxygen molecules • Hemoglobin Saturation • The percentage of heme units in a hemoglobin molecule that contain bound oxygen • Environmental Factors Affecting Hemoglobin • PO2 of blood • Blood pH • Temperature • Metabolic activity within RBCs • Oxygen–Hemoglobin Saturation Curve • A graph relating the saturation of hemoglobin to partial pressure of oxygen • Higher P O2 results in greater Hb saturation • Curve rather than a straight line because Hb changes shape each time a molecule of O is bound 2 • Each O bo2nd makes next O binding e2sier • Allows Hb to bind O when2O levels 2re low • Oxygen Reserves • O diffuses 2 • From peripheral capillaries (high P ) O2 • Into interstitial fluid (low P )O2 • Amount of O rel2ased depends on interstitial P O2 • Up to 3/4 may be reserved by RBCs • Carbon Monoxide • CO from burning fuels • Binds strongly to hemoglobin • Takes the place of O 2 • Can result in carbon monoxide poisoning • The Oxygen–Hemoglobin Saturation Curve • Is standardized for normal blood (pH 7.4, 37C) • When pH drops or temperature rises: • More oxygen is released • Curve shifts to right • When pH rises or temperature drops: • Less oxygen is released • Curve shifts to left • Hemoglobin and pH • Bohr effect is the result of pH on hemoglobin-saturation curve • Caused by CO 2 • CO 2iffuses into RBC • An enzyme, called carbonic anhydrase, catalyzes reaction with H 2 • Produces carbonic acid (H CO ) 2 3 • Dissociates into hydrogen ion (H ) and bicarbonate ion (HCO ) 3 • Hydrogen ions diffuse out of RBC, lowering pH • Hemoglobin and Temperature • Temperature increase = hemoglobin releases more oxygen • Temperature decrease = hemoglobin holds oxygen more tightly • Temperature effects are significant only in active tissues that are generating large amounts of heat • For example, active skeletal muscles • Hemoglobin and BPG • 2,3-bisphosphoglycerate (BPG) • RBCs generate ATP by glycolysis • Forming lactic acid and BPG • BPG directly affects O bin2ing and release • More BPG, more oxygen released • BPG Levels • BPG levels rise: • When pH increases • When stimulated by certain hormones • If BPG levels are too low: • Hemoglobin will not release oxygen • Fetal Hemoglobin • The structure of fetal hemoglobin • Differs from that of adult Hb • At the same P : O2 • Fetal Hb binds more O than 2dult Hb • Which allows fetus to take O from 2aternal blood • Carbon Dioxide Transport (CO ) 2 • Is generated as a by-product of aerobic metabolism (cellular respiration) • CO 2n the bloodstream can be carried three ways • Converted to carbonic acid • Bound to hemoglobin within red blood cells • Dissolved in plasma • Carbonic Acid Formation • 70% is transported as carbonic acid (H CO ) 2 3 + • Which dissociates into H and bicarbonate (HCO ) 3 • Hydrogen ions bind to hemoglobin • Bicarbonate Ions • Move into plasma by an exchange mechanism (the chloride shift) that takes in Cl ions without using ATP • CO Binding to Hemoglobin 2 • 23% is bound to amino groups of globular proteins in Hb molecule • Forming carbaminohemoglobin • Transport in Plasma • 7% is transported as CO dissolved in plasma 2 Control of Respiration • Peripheral and Alveolar Capillaries • Maintain balance during gas diffusion by: 1. Changes in blood flow and oxygen delivery 2. Changes in depth and rate of respiration • Local Regulation of Gas Transport and Alveolar Function • Rising P CO2levels 1. Relax smooth muscle in arterioles and capillaries 2. Increase blood flow • Coordination of lung perfusion and alveolar ventilation 1. Shifting blood flow • P CO2levels 1. Control bronchoconstriction and bronchodilation
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