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Respiratory Systems Chapter 9; 29.10.-01.11.2010 Overview Respiration Sequence of events that result in the exchange of oxygen and carbon dioxide between the external environment and the mitochondria Mitochondrial respiration Production of ATP by oxidation of carbohydrates, amino acids, or fatty acids; oxygen is consumed and carbon dioxide is produced Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview External respiration Gas exchange at the respiratory surface Internal respiration Gas exchange at the tissue Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Unicellular and small multicellular organisms rely on diffusion for gas exchange Larger organisms must rely on a combination of bulk flow and diffusion for gas exchange Bulk flow Ventilation Moving medium (air or water) over respiratory surface (lung or gill) Circulation Transport of gases in the circulatory system Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview Respiratory strategies of animals: Diffusion alone is too slow to maintain the rates of gas exchange needed to support the metabolism of larger animals. Larger organisms rely on a combination of bulk flow and diffusion for gas exchange. Figure 9.1 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Physics of Respiratory Systems Diffusion of gases Fick equation dQ/dt = D A (dC/dx) dQ/dt = Rate of diffusion D = diffusion coefficient (D) A = area of the membrane (A) dC/dx = gradient Difference in pressure (not concentration) To maximize diffusion respiratory surfaces are typically thin, with a large surface area Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Dalton’s Law of Partial Pressure The pressure exerted by a gas is related to the number of moles of the gas and the volume of the chamber Ideal gas law pV = nRT The ideal gas law is the equation of state of a hypothetical ideal gas. where p is the absolute pressure of the gas; V is the volume; n is the amoun of substance; R is the universal gas constant; and T is the absolute temperature. In SI units, p is measured in pascals; V in cubic metres; n in moles; and T in kelvin. R has the value 8.314472 J·K−1·mol−1 in SI units. Air is a mixture of gases Nitrogen (78%), oxygen (21%), argon (0.9%), and carbon dioxide (0.03%) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Dalton’s Law of Partial Pressure In a gas mixture each gas exerts its own partial pressure The sum of all partial pressures is equal to the total pressure of the mixture PressureTotal = Pressure1 + Pressure2 ... Pressuren Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Henry’s Law Gas molecules in the air must first dissolve in liquid in order to diffuse into a cell The concentration of gas in a liquid is proportional to its partial pressure Henry’s law [G] = Pgas Sgas [G] = concentration of the gas Pgas = partial pressure of the gas Sgas = solubility of the gas Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Henry’s Law Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.2b Diffusion Rates Graham’s law Diffusion rate is proportional to solubility/MW Combining the Fick equation with Henry’s law and Graham’s law Diffusion rate of a gas molecule is proportional to D A DPgas Sgas / X MW D - diffusion coefficient A - cross-sectional area DPgas - partial pressure gradient Sgas - solubility of the gas in the fluid X - diffusion distance MW - molecular weight of the gas Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings CO2 vs O2 O2 diffuses almost 300,000 times more slowly in water than in air Gases in Air and Water Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 9.1 Bulk Flow of Gases Fluids flow from areas of high pressure to areas of low pressure Boyle’s law P1V1 = P2V2 P1V1 = initial pressure and volume of the gas P2V2 = final pressure and volume of the gas For example, if you increase the volume of a chamber of gas, the pressure of the gas will decrease The rate of flow (Q) determined by the difference in pressure (DP) and the resistance to flow (R) Q = DP/R Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bulk Flow of Gases Liquids are incompressible Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.3 Surface Area to Volume Ratio As radius increases, volume increases faster than surface area As organisms grow larger, the ratio of surface area to volume decreases Larger size limits the surface area available for diffusion and increases the diffusion distance Only very small organisms can rely solely on the diffusion oxygen to support metabolism Larger animals must transport oxygen by bulk flow Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Surface Area to Volume Ratio As radius increases, volume increases faster than surface area Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.4 Respiratory Strategies Animals more than a few millimeters thick use one of three respiratory strategies Circulating the external medium through the body Sponges, cnidarians, and insects Diffusion of gases across the body surface accompanied by circulatory transport Cutaneous respiration Skin must be thin and moist Most aquatic invertebrates, some amphibians, eggs of birds Diffusion of gases across a specialized respiratory surface accompanied by circulatory transport Gills (evaginations) or lungs (invaginations) Vertebrates Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ventilation Ventilation of respiratory surfaces reduces the formation of static boundary layers (oxygen depletion in the immediate area) Types of ventilation Nondirectional Medium flows past the respiratory surface in an unpredictable pattern Tidal Medium moves in and out of the chamber Unidirectional Medium enters the chamber at one point and exits at another Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ventilation The pattern, but not the direction, of ventilation can change with environmental or metabolic conditions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Patterns of Ventilation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 9.2 Orientation of Medium and Blood Flow Gases enter the blood at the respiratory surface Movement of blood through the respiratory surface can affect efficiency of gas exchange Both the mode of ventilation and the orientation of the flow of the respiratory medium and the blood affect the efficiency of gas exchange Comparison of Po2 in medium and blood as they enter and leave the respiratory surface Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Orientation of Medium and Blood Flow Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.6a–c Orientation of Medium and Blood Flow With unidirectional ventilation, the blood can flow in three ways relative to the flow of the medium Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.6d–f Ventilation of Water and Air Because of the different physical properties of air and water, animals use different strategies depending on the medium in which they live Differences [Oair] is 30 times greater than [Owater] 30 times more water than air must be ventilated to get the same amount of oxygen Water is more dense and viscous than air It is more difficult to ventilate water Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Ventilation of Water vs. Air Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Table 9.1 Ventilation of Water vs. Air Ventilation strategies Unidirectional Most water breathers Allows for countercurrent exchange Tidal Air-breathers Air flows easily; it would require too much work for tidal ventilation of water Air-filled tubes Insects High diffusion rates of gases in air Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Sponges and Cnidarians Circulate external medium through an internal cavity Sponges Flagella move water in through ostia and out through the osculum Cnidarians Muscle contractions move water in and out through the mouth Gases diffuse directly in and out of cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.7 Molluscs Two strategies for ventilating gills (ctenidia) Snails and clams Cilia on gills move water across the gills unidirectionally Flow is countercurrent Cephalopods Muscular contractions of mantle propel water unidirectionally past the gills in the mantle cavity Flow is countercurrent Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Molluscs Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.8 Crustaceans Filter feeding (barnacles) or small species (copepods) lack gills and rely on diffusion Shrimp, crabs, and lobsters have gills derived from modified appendages within a branchial cavity Movements of gill bailer propels water out of branchial chamber; negative pressure sucks water across gills Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.9 Echinoderms Most sea stars and sea urchins use their tube feet for gas exchange Water is sucked in, and exits through, the madreporite External gill-like structures (respiratory papulae) can absorb oxygen from water Cilia move water over the surface Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.10a Echinoderms Brittle stars and sea cucumbers have internal invaginations Brittle stars use cilia to move water into saclike cavity (bursae) Sea cucumbers use muscular contractions of the cloaca and the respiratory tree to pump water tidally via the anus Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.10b Jawless Fishes Lamprey and hagfish have multiple pairs of gill sacs Hagfish Muscular pump (velum) propels water through respiratory cavity Water enters the mouth and leaves through the gill opening Flow is unidirectional Blood flow is countercurrent Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.11a Jawless Fishes Lamprey When not feeding, ventilation is similar to hagfish When feeding, the mouth is attached to a prey Ventilation is tidal through gill openings Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.11b Elasmobranchs Steps in ventilation Expand buccal cavity Increased volume sucks water into buccal cavity via mouth and spiracles Mouth and spiracles close Muscles around the buccal cavity contract, forcing water past gills and out the gill slits Blood flow is countercurrent Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.12 Teleost Fishes Gills are located in the opercular cavity protected by the flaplike operculum Steps in ventilation With the mouth open and the opercular valve closed, the buccal and opercular cavities expand Pressure decreases and sucks water in through mouth Mouth closes Floor of buccal cavity raises and operculum expands Pressure pushes water into opercular cavity Opercular valve opens and water leaves through the opercular slit Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Teleost Fishes Active fish can also use ram ventilation Swimming with mouth and opercular valve open Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Teleost Fishes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.13 Countercurrent Flow in Fish Gills Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.14 Ventilation and Gas Exchange in Air Two major animal lineages have colonized terrestrial habitats Vertebrates Amphibians Reptiles Birds Mammals Arthropods Crustaceans Chelicerates Insects Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Crustaceans Terrestrial crabs Respiratory structures and ventilation are similar to marine relatives, but Gills are stiff so they do not collapse in air Branchial cavity itself is highly vascularized and acts as the primary site of gas exchange Terrestrial isopods (woodlice and sowbugs) Have a thick layer of chitin on one side of the gill for support Anterior gills contain air-filled tubules (pseudotrachea) Gases diffuse from pseudotrachea into blood Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Chelicerates (Spiders and Scorpions) Have four book lungs 10–100 lamellae project into air-filled cavity Cavity opens to outside via spiracle Gases diffuse in and out Some spiders also have a tracheal system Series of air-filled tubes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.15 Insects Have an extensive tracheal system Air-filled tubes called tracheae Open to outside via spiracle Tracheae branch to form tracheoles Ends of tracheoles are filled with hemolymph Gases diffuse in and out Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.16 Insect Ventilation Mechanisms Contraction of abdominal muscles or movements of the thorax Tidal Air flows in and out of the same spiracles Unidirectional Air enters anterior spiracles, flows through tracheae, and exits abdominal spiracles Ram ventilation (draft ventilation) in some flying insects Expansion and contraction of tracheae Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Discontinuous Gas Exchange in Insects Phase 1 (closed phase) Spiracles are closed; no gas exchange with environment O2 used and CO2 converted to HCO3– Decrease in total pressure in tracheae Phase 2 (flutter phase) Spiracles open and close in rapid succession (“flutter”) Air enters tracheae Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Discontinuous Gas Exchange in Insects Phase 3 Excess CO2 can no longer be stored as HCO3– Total pressure in tracheae increases Spiracles open and CO2 is released Adaptive value of discontinuous gas exchange is unknown Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Air Breathing in Fish Air breathing has evolved multiple times in fishes Types of respiratory structures Reinforced gills that do not collapse in air Highly vascularized mouth or pharyngeal cavity Highly vascularized stomach Specialized pockets of the gut Lungs Ventilation is tidal using buccal force similar to other fish Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Air Breathing in Fish Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.19 Amphibians Types of respiratory structures Cutaneous respiration External gills Simple bilobed lungs More complex lungs in terrestrial frogs and toads Ventilation is tidal using a buccal force pump Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Amphibians Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.20 Reptiles Most have two lungs In snakes, one lung is reduced or absent Can be simple sacs with honeycombed walls or highly divided chambers in more active species More divisions create more surface area Tidal ventilation Generally rely on suction pumps May supplement this with buccal pump Separation of feeding and respiratory muscles Two phases Inspiration and expiration Several mechanisms change volume of the chest cavity Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Reptiles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.21 Birds Lungs are stiff and change little in volume Lungs are between a series of air sacs that act as bellows Posterior and anterior air sacs Gas exchange occurs as air flows through parabronchi in lungs Air flow through parabronchi is unidirectional Blood flow is crosscurrent Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.22a Bird Ventilation Requires two cycles of inhalation and exhalation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.23 Mammals Two main parts to respiratory system Upper respiratory tract Mouth, nasal cavity, pharynx, trachea Lower respiratory tract Bronchi and gas exchange surfaces (alveoli) Alveoli are the site of gas exchange Thin wall of type I alveolar cells Type II surfactant cells secrete fluid Outer surface of alveoli are covered in capillaries Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mammals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.24 Pleural Sac Each lung is surrounded by a pleural sac Two layers of cells with small space between them Pleural cavity Pleural cavity contains a small volume of pleural fluid Intrapleural pressure is subatmospheric Keeps lung expanded Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.25 Mammalian Tidal Ventilation: Inspiration Inhalation Motor neuron stimulates inspiratory muscles Contraction of the external intercostals and diaphragm Ribs move outwards and the diaphragm moves downward Volume of thorax ; intrathoracic pressure Transpulmonary pressure gradient Lungs expand and air is pulled in Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mammalian Tidal Ventilation: Exhalation Exhalation Nerve stimulation of inspiratory muscles stops Muscles relax Ribs and diaphragm return to their original positions Volume of thorax ; intrathoracic pressure Passive recoil of the lungs pushes air out During rapid, heavy breathing, forced exhalation is by contraction of the internal intercostal muscles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mammalian Ventilation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.26 Lung Compliance and Surfactants Lung compliance How easily the lungs stretch during inhalation Surface tension in alveolar fluid lowers compliance Surfactants Reduces surface tension by disrupting the cohesive forces between water molecules In humans, surfactant synthesis does not begin until late gestation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Airway Resistance Airway diameter affects resistance to air flow As diameter , resistance Higher resistance requires a large transpulmonary pressure gradient Parasympathetic nerve stimulation causes bronchoconstriction Sympathetic nerve stimulation causes bronchodilation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Dead Space Tidal volume (VT) Volume of air moved in one ventilatory cycle Dead space (VD) Air that does not participate in gas exchange Two components Anatomical dead space Volume of trachea and bronchi Alveolar dead space Volume of alveoli that are not perfused Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Dead Space Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.27 Alveolar Ventilation Alveolar ventilation volume (VA) Volume of fresh air that enters alveoli with each respiratory cycle VA = VT – VD Alveolar minute ventilation Volume of fresh air that enters alveoli each minute VA = f(VT – VD) f = breathing rate in breaths per minute Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Lung Volumes and Capacities Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.28 Ventilation–Perfusion Matching Efficient gas exchange at respiratory surface requires matching of ventilation and blood flow Arterioles dilate or constrict to distribute blood to well-ventilated alveoli For example, low Po2 in alveolus causes constriction of arteriole Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Gas Transport Sponges, cnidarians, and insects circulate external medium (water or air) past almost every body cell and can rely on diffusion Larger animals use circulatory systems Transport of gases in blood Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Oxygen Transport in the Blood Solubility of oxygen in aqueous fluids is low Metalloproteins (respiratory pigments) Proteins containing metal ions which reversibly bind to oxygen and Increase oxygen carrying capacity by 50-fold Three major types of respiratory pigments Hemoglobins Hemocyanins Hemerythrins Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Hemoglobins Vertebrates, nematodes, some annelids, crustaceans, and insects Globin protein bound to a heme molecule containing iron Usually within blood cells Appears red when oxygenated Myoglobin is a type of hemoglobin found in muscles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.29 Fetal hemoglobin (human) Fetal Hemoglobin 2 a chains 2 g chains 37 a.a. different High hematocrit in fetus Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Adult Hemoglobin 2 a chains 2 b chains Hemocyanins and Hemerythrins Hemocyanins Arthropods and molluscs Contain copper Usually dissolved in the hemolymph Appears blue when oxygenated Hemerythrins Sipunculids, priapulids, brachiopods, some annelids Contains iron directly bound to protein Usually found inside coelomic cells Appears violet-pink when oxygenated Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Oxygen Equilibrium Curves Relationship between Po2 in plasma and the percent of oxygenated respiratory pigment in blood As Po2 increases more pigment molecules will bind oxygen, until 100% saturation P50 Po2 at which pigment is 50% saturated Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.30 Shapes of Oxygen Equilibrium Curves Can be hyperbolic or sigmoidal Myoglobin has a hyperbolic curve because each oxygen binds independently Hemoglobin has a sigmoidal curve because of cooperativity Hemoglobin has a higher affinity for oxygen as more of its heme groups bind to oxygen Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Shapes of Oxygen Equilibrium Curves Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.31 Conditions That Affect Oxygen Affinity pH and PCO2 Bohr effect or shift Decrease in pH or increase in PCO2 reduces oxygen affinity; “right shift” P50 is increased Facilitates oxygen transport to active tissues and facilitates oxygen binding at the respiratory surfaces Root effect A Bohr effect with a reduction in the oxygen carrying capacity Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Bohr Affect and Root Affect Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.32 and Figure 9.33 Conditions That Affect Oxygen Affinity Temperature Increases in temperature decrease oxygen affinity; “right shift” P50 is increased Promotes oxygen delivery to warm muscles during exercise Organic modulators (e.g., DPG) Increases in these modulators decrease oxygen affinity; “right shift” Helps oxygen unloading at tissues Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Temperature and Organic Modulators Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.34 and Figure 9.35 •Carbon monoxide (carboxyhemoglobin HbCO) - colorless, tasteless, odourless, non-irritant (not detectable in inhaled air) - CO binds to Fe2+ in heme, competes with O2 CO 200x greater affinity for Hb than O2 (in mixture 0.1% CO & 21% O2, half Hb will carry CO) - reduces HbO2 capacity - air breathers more sensitive to CO2 than O2 decreased HbO2 due to increased HbCO does not activate a physiological warning response homeostasis fails hypoxia Carbon Dioxide Transport in the Blood CO2 is transported in three ways Small amounts of CO2 gas are transported in the plasma CO2 is more soluble in body fluids than O2 Some CO2 binds to proteins For example, carbaminohemoglobin Most CO2 is transported as bicarbonate (HCO3–) carbonic acid bicarbonate Carbonic anhydrase catalyzes the formation of HCO3– Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Transport of CO2 and H+ by Hb •Carbamino hemoglobin CO2 binds to amine-terminal end of each of the 4 globin chains •Protonated hemoglobin H+ binds to a.a residue in b chain and in a chain HbO2 + H+ ↔ O2 + HbH+ Deoxyhemoglobin acts as a proton acceptor and minimizes changes in pH Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Carbon Dioxide Transport in the Blood At respiratory surface, CO2 diffuses out of blood Carbaminohemoglobin releases CO2 Bicarbonate reaction goes “to the left” Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Carbon Dioxide Equilibrium Curve Relationship between PCO2 and total CO2 content of the blood Shape of the curve depends on the kinetics of HCO3– formation Deoxygenated blood can carry more CO2 than oxygenated blood (Haldane effect) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.36 Vertebrate Red Blood Cells (RBC) and CO2 Transport Carbonic anhydrase is located within RBCs Reactions to synthesize HCO3– occur in the RBCs HCO3– is exchanged for Cl– in the plasma Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.37 Dissolved CO2 in plasma 5% in RBC 3% Carbamino Pr in plasma <1% Carbamino Hb in RBC 12% HCO3- in RBC 23% in plasma 57% Fig. 10.37 Carbonic anhydrase (CA) H2O + CO2 H2CO3 Reversible reaction CO2 Excretion and Body Fluid pH Pco2 affects the [HCO3–] and pH of body fluids As Pco2 , [HCO3–] and pH (i.e., [H+] ) Reaction goes “to the right” As Pco2 , [HCO3–] and pH (i.e., [H+] ) Reaction goes “to the left” Changes in ventilation affect body fluid pH Hyperventilation causes Pco2 Hypoventilation causes Pco2 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fate of H+ in the body •production through metabolism of ingested foods (production of CO2) •shifts of H+ between compartments alkaline/acid tide following ingestion of heavy meal (stomach acid/alkaline pancreatic juices) muscle storage vs protection of the brain •buffering capacity of Hb, plasma proteins •excretion through lungs (CO2)/gills and kidneys (H+, HCO3- ) Respiratory acidosis (if lung ventilation is reduced and body CO2 ) Respiratory alkalosis (lung ventilation increased and body CO2 ) Metabolic acidosis (e.g. anaerobic metabolism) Metabolic alkalosis (e.g. vomiting) CO2 Excretion and Body Fluid pH Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.38 summary LIGANDS OF HEMOGLOBIN •OXYGEN (oxyhemoglobin), attaches to Fe2+ in heme units (4O2/Hb) Hb + O2 ↔ HbO2 when 1 or 2 of the heme subunits bind O2, small conformational changes occur and quaternary structure of entire molecule changes increased affinity for O2 and reduced affinity for H+ and for CO2 •CARBON DIOXIDE (carbamino hemoglobin) attaches to NH2-terminal end of globin chains (4CO2/Hb) Hb + CO2 ↔ HbCO2 Decreases Hb affinity for O2 •HYDROGEN ION (protonated hemoglobin) attaches to a.a. residue in globin chains (4H+/Hb) HHb+ + O2 ↔ HbO2 + H+ Decreases Hb affinity for O2 •2-3-DIPHOSPHOGLYCERATE attaches as bridge between b chains (1DPG/Hb) HbO2 + DPG ↔ HbDPG + O2 Decreases Hb affinity for O2 Regulation of Respiratory Systems Vertebrate respiratory and circulatory systems work together to regulate gas delivery by Regulating ventilation depth and rate Altering oxygen carrying capacity and affinity Altering perfusion Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Regulation of Ventilation Rhythmic firing of central pattern generators in the medulla initiate ventilatory movements via nerve signal Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.39 Regulation of Ventilation Chemoreceptors detect changes in CO2, H+, and O2 O2 is the primary regulator in waterbreathers CO2 is the primary regulator in air-breathers Chemosensory input modulates output of central pattern generators Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.40 REGULATION OF BREATHING - Medullary Respiratory Centre Inspiratory neurons respiratory muscles phasic (active ~2 sec, inactive ~3 sec) generate rhythmic breathing impose rhythm inhibit E neurons Expiratory neurons - not active during normal quiet breathing function during forced expiration continuously active if no I activity (i.e. not phasic) Rhythm influenced by neuronal inputs from: pulmonary stretch receptors pulmonary irritant receptors peripheral chemoreceptors central chemoreceptors Environmental Hypoxia Hypoxia Lower than normal Po2 in environment or blood Causes Environmental hypoxia For example, high altitude Inadequate ventilation (hypoventilation) Reduced blood hemoglobin content (anemia) Hypercapnia Higher than normal Po2 in environment or blood Hypocapnia Lower than normal Po2 in environment or blood Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Diving by air-breathing vertebrates Females Time underwater (%) 91% Avg dive duration (min) 22 min Max dive duration (min) 80 min Avge dive depth (m) 522 m Max dive depth (m) 1567 m e.g. Northern Elephant Seals Males 90% 22 min 89 min 366 m 1581 m Source: Stewart & DeLong, 1995, J. Mammalogy Problems: infrequent opportunities to air breath CNS must receive O2 fetus must receive O2 submerge to great depths lung compression “bends” lung re-inflation Solutions? Oxygen stores large blood volume high hematocrit high myoglobin large spleen 14% of body mass 60% (vs. 7%) (vs. 45%) Diving responses in seals •Exhale before diving lungs collapse (at 40 m depth) non-respiratory air ducts do not collapse (cartilage rings) residual volume forced into non-respiratory ducts •Inhibition of breathing receptors detect water on face inhibit inspiratory neurons •Selective perfusion of tissues blood flow to CNS, eye, heart, placenta increase RBC count by release of RBC from spleen stop blood flow to most other tissues O2 unloads from myoglobin anaerobic metabolism & lactic acid storage reduced metabolism on prolonged dives, pH stable BREATHING AT HIGH ALTITUDE Problems: Po2 declines with altitude Sea level 3000 m 6000 m Po2 kPa 21.2 14.5 9.7 PAo2 kPa 13.8 8.9 5.3 9000 m 6.3 2.8 hypoxia = insufficient O2 to tissues breathlessness, dizziness, nausea, headache Solutions ?: PAo2 (systemic vasodilation & New problems? hyperventilation ?? pulmonary vasoconstriction) hypocapnia hypoventilation uneven breathing, conflict between peripheral & central chemoreceptors reduced blood flow to alveoli Acclimation to Altitude Polycythemia - increased RBC production by bone marrow - increased Hb content - increased blood volume Vascular responses - increased heart rate & cardiac output - capillary proliferation Regular hyperventilation -central chemoreceptors not stimulated by low PACO2 -peripheral chemoreceptors adjust respiration to PAO2 Renal compensation (1-2 weeks) -increased HCO3- excretion, stabilize pH at 7.5 Increased 2,3-DPG decreased O2 affinity of Hb enhances unloading of O2 at tissues High-Altitude Hypoxia Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 9.41