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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 16 Respiratory Physiology 16-1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 16 Outline Respiratory Structures Physical Aspects of Ventilation Mechanics of Breathing Pulmonary Disorders Factors Affecting Ventilation Control of Ventilation Hemoglobin CO2 Transport & Acid-Base Balance Exercise & Altitude Effects 16-2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiration Encompasses 3 related functions: ventilation, gas exchange, & 02 utilization (cellular respiration) Ventilation moves air in & out of lungs for gas exchange with blood (external respiration) Gas exchange between blood & tissues, & O2 use by tissues is internal respiration Gas exchange is passive via diffusion 16-3 Respiratory Structures 16-4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of Respiratory System Air passes from mouth to trachea to right & left bronchi to bronchioles to terminal bronchioles to respiratory bronchioles to alveoli Fig 16.4 16-5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of Respiratory System continued Gas exchange occurs only in respiratory bronchioles & alveoli (= respiratory zone) All other structures constitute the conducting zone Are polyhedral in shape & clustered at ends of respiratory bronchioles, like units of honeycomb Fig 16.4 16-6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of Respiratory System continued Gas exchange occurs across the 300 million alveoli (60-80 m2 total surface area) Only 2 thin cells are between lung air & blood: 1 alveolar & 1 endothelial cell Insert 16.1 Fig 16.1 16-7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Alveoli Are polyhedral in shape & clustered at ends of respiratory bronchioles, like units of honeycomb Air in 1 cluster can pass to others through pores 16-8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Conducting Zone Warms & humidifies inspired air Mucus lining filters & cleans inspired air Mucus moved by cilia to be expectorated Insert fig. 16.5 Fig 16.5 16-9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thoracic Cavity Is created by the diaphragm, a dome-shaped sheet of skeletal muscle Contains heart, large blood vessels, trachea, esophagus, thymus, & lungs Below diaphragm is abdominopelvic cavity Contains liver, pancreas, GI tract, spleen, & genitourinary tract Intrapleural space is thin fluid layer between visceral pleura covering lungs & parietal pleura lining thoracic cavity walls 16-10 Physical Aspects of Ventilation 16-11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Physical Aspects of Ventilation Ventilation results from pressure differences induced by changes in lung volumes Air moves from higher to lower pressure Compliance, elasticity, & surface tension of lungs influence ease of ventilation 16-12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intrapulmonary & Intrapleural Pressures Visceral & parietal pleurae normally adhere to each other so that lungs remain in contact with chest walls Fig 16.8 & expand & contract with thoracic cavity 16-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intrapulmonary & Intrapleural Pressures During inspiration, intrapulmonary pressure is about -3 mm Hg pressure; during expiration is about +3 mm Hg Positive transmural pressure (intrapulmonary - intrapleural pressure) keeps lungs inflated 16-14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Boyle’s Law (P = 1/V) Implies that changes in intrapulmonary pressure occur as a result of changes in lung volume Pressure of gas is inversely proportional to volume Increase in lung volume decreases intrapulmonary pressure causing inspiration Decrease in lung volume raises intrapulmonary pressure causing expiration 16-15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Compliance Is how easily lung expands with pressure Or change in lung volume per change in transmural pressure (DV/DP) Is reduced by factors that cause resistance to distension 16-16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Elasticity Is tendency to return to initial size after distension Due to high content of elastin proteins Elastic tension increases during inspiration & is reduced by recoil during expiration 16-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Surface Tension (ST) And elasticity are forces that promote alveolar collapse & resist distension Lungs secrete & absorb fluid, normally leaving a thin film of fluid on alveolar surface Fluid absorption occurs by osmosis driven by Na+ active transport Fluid secretion is driven by active transport of Clout of alveolar epithelial cells This film causes ST because H20 molecules are attracted to other H20 molecules Force of ST is directed inward, raising pressure in alveoli 16-18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Surface Tension continued Law of Laplace states that pressure in alveolus is directly proportional to ST; & inversely to radius of alveoli Thus, pressure in smaller alveoli would be greater than in larger alveoli, if ST were same in both Fig 16.11 Insert fig. 16.11 16-19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Surfactant Consists of phospholipids secreted by type II alveolar cells Lowers ST by getting between H20 molecules, reducing their ability to attract each other via hydrogen bonding Fig 16.12 16-20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Surfactant continued Prevents ST from collapsing alveoli Surfactant secretion begins in late fetal life Premies are often born with immature surfactant system (= Respiratory Distress Syndrome or RDS) Have trouble inflating lungs In adults, septic shock may cause acute respiratory distress syndrome (ARDS) which decreases compliance & surfactant secretion 16-21 Mechanics of Breathing 16-22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanics of Breathing Pulmonary ventilation consists of inspiration (= inhalation) & expiration (= exhalation) Accomplished by alternately increasing & decreasing volumes of thorax & lungs Fig 16.13 expiration inspiration 16-23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Quiet Breathing Inspiration occurs mainly because diaphragm contracts, increasing thoracic volume vertically Parasternal & external intercostal contraction contributes a little by raising ribs, increasing thoracic volume laterally Expiration is due to passive recoil Fig 16.14 16-24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Deep Breathing Inspiration involves contraction of extra muscles to elevate ribs: scalenes, pectoralis minor, & sternocleidomastoid muscles Expiration involves contraction of internal intercostals & abdominal muscles Fig 16.14 16-25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanics of Pulmonary Ventilation Insert fig. 16.15 Fig 16.15 16-26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Function Tests Assessed clinically by spirometry, a method that measures volumes of air moved during inspiration & expiration Anatomical dead space is air in conducting zone where no gas exchange occurs 16-27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Function Tests continued Tidal volume is amount of air expired/breath in quiet breathing Vital capacity is amount of air that can be forcefully exhaled after a maximum inhalation = sum of inspiratory reserve, tidal volume, & expiratory reserve Fig 16.16 16-28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-29 Pulmonary Disorders 16-30 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Restrictive Disorders Are characterized by reduced vital capacity but with normal forced vital capacity E.g. pulmonary fibrosis 16-31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Obstructive Disorders Have normal vital capacity but expiration is retarded E.g. asthma Diagnosed by tests, such as forced expiratory volume, that measure rate of expiration Insert fig. 16.17 Fig 16.17 16-32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Disorders Are frequently accompanied by dyspnea, a feeling of shortness of breath Asthma results from episodes of obstruction of air flow thru bronchioles Caused by inflammation, mucus secretion, & broncho constriction Inflammation contributes to increased airway responsiveness to agents that promote bronchial constriction Provoked by allergic reactions that release IgE, by exercise, by breathing cold, dry air, or by aspirin 16-33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Disorders continued Emphysema is a chronic, progressive condition that destroys alveolar tissue, resulting in fewer, larger alveoli Reduces surface area for gas exchange & ability of bronchioles to remain open during expiration Collapse of bronchiole during expiration causes air trapping, decreasing gas exchange Commonly occurs in long-term smokers Cigarette smoking stimulates macrophages & leukocytes to secrete protein-digesting enzymes that destroy tissue 16-34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. emphysema normal lung Fig 16.18 16-35 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Disorders continued Sometimes lung damage leads to pulmonary fibrosis instead of emphysema Characterized by accumulation of fibrous connective tissue Occurs from inhalation of particles <6m in size, such as in black lung disease (anthracosis) from coal dust 16-36 Factors Affecting Gas Exchange 16-37 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Partial Pressure of Gases Partial pressure is pressure that a particular gas in a mixture exerts independently Dalton’s Law states that total pressure of a gas mixture is the sum of partial pressures of each gas in mixture Atmospheric pressure at sea level is 760 mm Hg PATM = PN2 + P02 + PC02 + PH20 = 760 mm Hg 16-38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gas Exchange in Lungs Is driven by differences in partial pressures of gases between alveoli & capillaries Fig 16.20 16-39 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Gas Exchange in Lungs continued Is facilitated by enormous surface area of alveoli, short diffusion distance between alveolar air & capillaries, & tremendous density of capillaries Fig 16.21 16-40 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Partial Pressures of Gases in Blood When blood & alveolar air are at equilibrium the amount of O2 in blood reaches a maximum value Henry’s Law says that this value depends on solubility of O2 in blood (a constant), temperature of blood (a constant), & partial pressure of O2 So the amount of O2 dissolved in blood depends directly on its partial pressure (PO2), which varies with altitude 16-41 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blood PO2 & PCO2 Measurements Provide good index of lung function At normal PO2 arterial blood has about 100 mmHg PO2 PO2 is about 40 mmHg in systemic veins PC02 is 46 mmHg in systemic veins Fig 16.23 16-42 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary Circulation Rate of blood flow through pulmonary circuit equals flow through systemic circulation But is pumped at lower pressure (about 15 mm Hg) Pulmonary vascular resistance is low Low pressure produces less net filtration than in systemic capillaries Avoids pulmonary edema Pulmonary arterioles constrict where alveolar PO2 is low & dilate where high This matches ventilation to perfusion 16-43 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lung Ventilation/Perfusion Ratios Normally, alveoli at apex of lungs are underperfused & overventilated Alveoli at base are overperfused & underventilated Insert fig. 16.24 Fig 16.24 16-44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Disorders Caused by High Partial Pressures of Gases Total atmospheric pressure increases by an atmosphere for every 10m below sea level At depth, increased O2 & N2 can be dangerous to body Breathing 100% O2 at < 2 atmospheres can be tolerated for few hrs O2 toxicity can develop rapidly at > 2 atmospheres Probably because of oxidation damage 16-45 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Disorders Caused by High Partial Pressures of Gases At sea level, nitrogen is physiologically inert It dissolves slowly in blood Under hyperbaric conditions takes more than hour for dangerous amounts to accumulate Nitrogen narcosis resembles alcohol intoxication Amount of nitrogen dissolved in blood as diver ascends decreases due to decrease in PN2 If ascent is too rapid, decompression sickness occurs as bubbles of nitrogen gas form in tissues & enter blood, blocking small blood vessels & producing “bends” 16-46 Control of Ventilation 16-47 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brain Stem Respiratory Centers Automatic breathing is generated by a rhythmicity center in medulla oblongata Fig 16.25 Consists of inspiratory neurons that drive Insert fig. 16.25 inspiration & expiratory neurons that inhibit inspiratory neurons Their activity varies in a reciprocal way & may be due to pacemaker neurons 16-48 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Brain Stem Respiratory Centers continued Inspiratory neurons stimulate spinal motor neurons that innervate respiratory muscles Expiration is passive & occurs when inspiratories are inhibited 16-49 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pons Respiratory Centers Activities of medullary rhythmicity center is influenced by centers in pons Apneustic center promotes inspiration by stimulating inspiratories in medulla Pneumotaxic center antagonizes apneustic center, inhibiting inspiration 16-50 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemoreceptors Automatic breathing is influenced by activity of chemoreceptors that monitor blood PC02, P02, & pH Central chemoreceptors are in medulla Peripheral chemoreceptors are in large arteries near heart (aortic bodies) & in carotids (carotid bodies) Fig 16.26 16-51 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CNS Control of Breathing Fig 16.27 16-52 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Effects of Blood PC02 & pH on Ventilation Chemoreceptors modify ventilation to maintain normal CO2, O2, & pH levels PCO2 is most crucial because of its effects on blood pH H20 + C02 H2C03 H+ + HC03- Hyperventilation causes low C02 (hypocapnia) Hypoventilation causes high C02 (hypercapnia) 16-53 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Effects of Blood PC02 & pH on Ventilation continued Brain chemoreceptors are responsible for greatest effects on ventilation H+ can't cross BBB but C02 can, which is why it is monitored & has greatest effects Rate and depth of ventilation adjusted to maintain arterial PC02 of 40 mm Hg Peripheral chemoreceptors do not respond to PC02, only to H+ levels 16-54 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig 16.30 16-55 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chemoreceptor Control of Breathing Fig 16.29 16-56 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Effects of Blood P02 on Ventilation Low blood P02 (hypoxemia) has little affect on ventilation Does influence chemoreceptor sensitivity to PC02 P02 has to fall to about half normal before ventilation is significantly affected Emphysema blunts chemoreceptor response to PC02 Oftentimes ventilation is stimulated by hypoxic drive rather than PC02 16-57 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Effects of Pulmonary Receptors on Ventilation Lungs have receptors that influence brain respiratory control centers via sensory fibers in vagus Unmyelinated C fibers are stimulated by noxious substances such as capsaicin Causes apnea followed by rapid, shallow breathing Irritant receptors are rapidly adapting; respond to smoke, smog, & particulates Causes cough Hering-Breuer reflex is mediated by stretch receptors activated during inspiration Inhibits respiratory centers to prevent overinflation of lungs 16-58 Hemoglobin 16-59 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hemoglobin (Hb) & 02 Transport Loading of Hb with O2 occurs in lungs; unloading in tissues Affinity of Hb for O2 changes with a number of physiological variables 16-60 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hemoglobin (Hb) & 02 Transport Each Hb has 4 globin polypeptide chains & 4 heme groups that bind 02 Each heme has a ferrous ion that can bind 1 02 So each Hb can carry 4 02s Fig 16.33 16-61 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hemoglobin (Hb) & 02 Transport continued Most 02 in blood is bound to Hb inside RBCs as oxyhemoglobin Each RBC has about 280 million molecules of Hb Hb greatly increases 02 carrying capacity of blood Insert fig. 16.32 Fig 16.32 16-62 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hemoglobin (Hb) & 02 Transport continued Methemoglobin contains ferric iron (Fe3+) -- the oxidized form Lacks electron to bind with 02 Blood normally contains a small amount Carboxyhemoglobin is heme combined with carbon monoxide Bond with carbon monoxide is 210 times stronger than bond with oxygen So heme can't bind 02 16-63 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hemoglobin (Hb) & 02 Transport continued 02-carrying capacity of blood depends on its Hb levels In anemia, Hb levels are below normal In polycythemia, Hb levels are above normal Hb production controlled by erythropoietin (EPO) Production stimulated by low P02 in kidneys Hb levels in men are higher because androgens promote RBC production 16-64 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hemoglobin (Hb) & 02 Transport continued High P02 of lungs favors loading; low P02 in tissues favors unloading Ideally, Hb-02 affinity should allow maximum loading in lungs & unloading in tissues 16-65 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oxyhemoglobin Dissociation Curve Gives % of Hb sites that have bound 02 at different P02s Reflects loading & unloading of 02 Differences in % saturation in lungs & tissues are shown at right In steep part of curve, small changes in P02 cause big changes in % saturation Fig 16.34 16-66 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oxyhemoglobin Dissociation Curve Fig 16.35 Is affected by changes in Hb-02 affinity caused by pH & temperature Affinity decreases when pH decreases (Bohr Effect) or temp increases Occurs in tissues where temp, C02 & acidity are high Causes Hb-02 curve to shift right & more unloading of 02 16-67 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Effect of 2,3 DPG on 02 Transport RBCs have no mitochondria; can’t perform aerobic respiration 2,3-DPG is a byproduct of glycolysis in RBCs Its production is increased by low 02 levels Causes Hb to have lower 02 affinity, shifting curve to right In anemia, total blood Hb levels fall, causing each RBC to produce more DPG Fetal hemoglobin (HbF) has 2 g-chains in place of b-chains of HbA HbF can’t bind DPG, causing it to have higher 02 affinity Facilitates 02 transfer from mom to baby 16-68 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sickle-cell Anemia Sickle-cell anemia affects 8-11% of African Americans HbS has valine substituted for glutamic acid at 1 site on b chains At low P02, HbS crosslinks to form a “paracrystalline gel” inside RBCs Makes RBCs less flexible & more fragile Fig 16.36 16-69 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thalassemia Thalassemia affects primarily people of Mediterranean descent Has decreased synthesis of a or b chains; increased synthesis of g chains 16-70 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Myoglobin Is a red pigment found exclusively in striated muscle Slow-twitch skeletal & cardiac muscle fibers are rich in myoglobin 16-71 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Myoglobin Has only 1 globin; binds only 1 02 Has higher affinity for 02 than Hb; is shifted to extreme left Releases 02 only at low P02 Serves in 02 storage, particularly in heart during systole Insert fig. 13.37 Fig 16.37 16-72 CO2 Transport & Acid-Base Balance 16-73 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. C02 Transport C02 transported in blood as dissolved C02 (10%), carbaminohemoglobin (20%), & bicarbonate ion, HC03-, (70%) In RBCs carbonic anhydrase catalyzes formation of H2CO3 from C02 + H2O 16-74 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chloride Shift High C02 levels in tissues causes the reaction C02 + H2O H2C03 H+ + HC03- to shift right in RBCs Results in high H+ & HC03- levels in RBCs H+ is buffered by proteins HC03- diffuses down concentration & charge gradient into blood causing RBC to become more + So Cl- moves into RBC (chloride shift) 16-75 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chloride Shift Fig 16.38 16-76 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Reverse Chloride Shift lungs, C02 + H2O H2C03 H+ + HC03-, moves to left as C02 is breathed out Binding of 02 to Hb decreases its affinity for H+ H+ combines with HC03& more C02 is formed Cl- diffuses down concentration & charge gradient out of RBC (reverse chloride shift) In Fig 16.39 16-77 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acid-Base Balance in Blood Blood pH is maintained within narrow pH range by lungs & kidneys (normal = 7.4) Most important buffer in blood is bicarbonate H20 + C02 H2C03 H+ + HC03Excess H+ is buffered by HC03Kidney's role is to excrete H+ into urine 16-78 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Effect of Bicarbonate on Blood pH Fig 16.40 Insert fig. 16.40 16-79 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acid-Base Balance in Blood continued 2 major classes of acids in body: A volatile acid can be converted to a gas E.g. C02 in bicarbonate buffer system can be breathed out H20 + C02 H2C03 H+ + HC03All other acids are nonvolatile & cannot leave blood E.g. lactic acid, fatty acids, ketone bodies 16-80 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acid-Base Balance in Blood continued Acidosis is when pH < 7.35; alkalosis is pH > 7.45 Respiratory acidosis caused by hypoventilation Causes rise in blood C02 & thus carbonic acid Respiratory alkalosis caused by hyperventilation Results in too little C02 16-81 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acid-Base Balance in Blood continued Metabolic acidosis results from excess of nonvolatile acids E.g. excess ketone bodies in diabetes or loss of HC03- (for buffering) in diarrhea Metabolic alkalosis caused by too much HC03- or too little nonvolatile acids (e.g. from vomiting out stomach acid) 16-82 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acid-Base Balance in Blood continued Normal pH is obtained when ratio of HCO3- to C02 is 20 : 1 Henderson-Hasselbalch equation uses C02 & HCO3levels to calculate pH: pH = 6.1 + log = [HCO3-] [0.03PC02] 16-83 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiratory Acid-Base Balance Ventilation usually adjusted to metabolic rate to maintain normal CO2 levels With hypoventilation not enough CO2 is breathed out in lungs Acidity builds, causing respiratory acidosis With hyperventilation too much CO2 is breathed out in lungs Acidity drops, causing respiratory alkalosis 16-84 Exercise & Altitude Effects 16-85 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ventilation During Exercise During exercise, arterial PO2, PCO2, & pH remain fairly constant Fig 16.41 16-86 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ventilation During Exercise During exercise, breathing becomes deeper & more rapid, delivering much more air to lungs (hyperpnea) 2 mechanisms have been proposed to underlie this increase: With neurogenic mechanism, sensory activity from exercising muscles stimulates ventilation; and/or motor activity from cerebral cortex stimulates CNS respiratory centers With humoral mechanism, either PC02 & pH may be different at chemoreceptors than in arteries Or there may be cyclic variations in their values that cannot be detected by blood samples 16-87 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lactate Threshold Is maximum rate of oxygen consumption before blood lactic acid levels rise as a result of anaerobic respiration Occurs when 50-70% maximum 02 uptake has been reached Endurance-trained athletes have higher lactate threshold, because of higher cardiac output Have higher rate of oxygen delivery to muscles & greater numbers of mitochondria & aerobic enzymes 16-88 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acclimatization to High Altitude Involves increased ventilation, increased DPG, & increased Hb levels Hypoxic ventilatory response initiates hyperventilation which decreases PC02 which slows ventilation Chronic hypoxia increases NO production in lungs which dilates capillaries there NO binds to Hb & is unloaded in tissues where may also increase dilation & blood flow NO may also stimulate CNS respiratory centers Altitude increases DPG, causing Hb-02 curve to shift to right Hypoxia causes kidneys to secrete EPO which increases RBCs 16-89