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Chapter 42: Gas Exchange

Chapter 42: Gas Exchange. Why is gas exchange important? Aerobic organisms need O 2 for oxidative phosphorylation (making ATP) CO 2 from citric acid cycle must be removed . Respiratory medium (air or water). Respiratory surface. CO 2. O 2. Organismal level. Circulatory system.

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Chapter 42: Gas Exchange

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  1. Chapter 42: Gas Exchange • Why is gas exchange important? • Aerobic organisms need O2 for oxidative phosphorylation (making ATP) • CO2 from citric acid cycle must be removed

  2. Respiratorymedium(air or water) Respiratorysurface CO2 O2 Organismal level Circulatory system Cellular level Energy-richmoleculesfrom food ATP Cellular respiration Figure 42.19 The role of gas exchange in bioenergetics

  3. Chapter 42: Gas Exchange • Why is gas exchange important? • Aerobic organisms need O2 for oxidative phosphorylation (making ATP) • CO2 from citric acid cycle must be removed • How have gas exchange systems changed as animals evolved? • Small, thin organisms – diffusion directly across skin • Larger organisms need a larger surface area (gills, trachea or lungs)

  4. Figure 42.20 Diversity in the structure of gills, external body surfaces functioning in gas exchange (a) Sea star. The gills of a sea star are simple tubular projections of the skin. The hollow core of each gillis an extension of the coelom(body cavity). Gas exchangeoccurs by diffusion across thegill surfaces, and fluid in thecoelom circulates in and out ofthe gills, aiding gas transport. The surfaces of a sea star’s tube feet also function in gas exchange. (b) Marine worm. Many polychaetes (marine worms of the phylum Annelida) have a pair of flattened appendages called parapodia on each body segment. The parapodia serve as gillsand also function incrawling and swimming. Gills Coelom Parapodia Gill Tube foot (c) Scallop. The gills of a scallop are long, flattened plates that project from the main body mass inside the hard shell. Cilia on the gills circulate water around the gill surfaces. (d) Crayfish. Crayfish and other crustaceans have long, feathery gills covered by the exoskeleton. Specialized body appendages drive water over the gill surfaces. Gills Gills

  5. Chapter 42: Gas Exchange • Why is gas exchange important? • Aerobic organisms need O2 for oxidative phosphorylation (making ATP) • CO2 from citric acid cycle must be removed • How have gas exchange systems changed as animals evolved? • Small, thin organisms – diffusion directly across skin • Larger organisms need a larger surface area (gills, trachea or lungs) • 3. How have fish gills evolved for maximal gas exchange?

  6. Oxygen-poorblood Gill arch Oxygen-richblood Lamella Blood vessel Gill arch 15% 40% 70% 5% 30% Water flow 60% 100% Operculum 90% Water flowover lamellaeshowing % O2 Blood flowthrough capillariesin lamellaeshowing % O2 Gillfilaments Countercurrent exchange Figure 42.21 The structure and function of fish gills At best, concurrent exchange would give blood O2 of 50%. Fish expend lots of energy ventilating – forcing water across gills to get O2.

  7. Chapter 42: Gas Exchange • Why is gas exchange important? • Aerobic organisms need O2 for oxidative phosphorylation (making ATP) • CO2 from citric acid cycle must be removed • How have gas exchange systems changed as animals evolved? • Small, thin organisms – diffusion directly across skin • Larger organisms need a larger surface area (gills, trachea or lungs) • How have fish gills evolved for maximal gas exchange? • Why don’t gills work on land? • Too dry for gills large surface area • External gas exchange will not occur • What adaptations do land animals have? • Internal exchange • Tracheal systems with many openings (spiracles)

  8. Body cell Air sacs Airsac Tracheole Tracheae Trachea Spiracle Body wall Air Myofibrils (a) The respiratory system of an insect consists of branched internal tubes that deliver air directly to body cells. Rings of chitin reinforce the largest tubes, called tracheae, keeping them from collapsing. Enlarged portions of tracheae form air sacs near organs that require a large supply of oxygen. Air enters the tracheae through openings called spiracles on the insect’s body surface and passes into smaller tubes called tracheoles. The tracheoles are closed and contain fluid (blue-gray). When the animal is active and is using more O2, most of the fluid is withdrawn into the body. This increases the surface area of air in contact with cells. Mitochondria Tracheoles (b) This micrograph shows cross sections of tracheoles in a tiny piece of insect flight muscle (TEM). Each of the numerous mitochondria in the muscle cells lies within about 5 µm of a tracheole. 2.5 µm Figure 42.22 Tracheal systems

  9. Chapter 42: Gas Exchange • Why is gas exchange important? • How have gas exchange systems changed as animals evolved? • How have fish gills evolved for maximal gas exchange? • Why don’t gills work on land? • What adaptations do land animals have? • Internal exchange • Tracheal systems with many openings (spiracles) • Lungs in spiders, terrestrial snails & vertebrates • 1 location for opening • Dense net of capillaries • What is the flow of air in our respiratory system? • Nostrils  nasal cavity  pharynx  larynx  trachea • Bronchi  bronchioles  alveoli

  10. Branch from the pulmonary vein (oxygen-rich blood) Branch from thepulmonaryartery(oxygen-poor blood) Terminal bronchiole Nasalcavity Pharynx Left lung Alveoli Larynx Esophagus 50 µm Trachea Right lung 50 µm Bronchus Bronchiole Diaphragm Heart Colorized SEM SEM Figure 42.23 The mammalian respiratory system • Mostly lined with cilia & thin layer of mucus

  11. Chapter 42: Gas Exchange • Why is gas exchange important? • How have gas exchange systems changed as animals evolved? • How have fish gills evolved for maximal gas exchange? • Why don’t gills work on land? • What adaptations do land animals have? • What is the flow of air in our respiratory system? • What is the difference between positive & negative breathing? • Positive – tongue pushes air down into lungs – frogs • Negative – air pulled down into lungs - us

  12. Rib cage expands asrib muscles contract Rib cage gets smaller asrib muscles relax Air inhaled Air exhaled Lung Diaphragm INHALATIONDiaphragm contracts(moves down) EXHALATIONDiaphragm relaxes(moves up) Figure 42.24 Negative pressure breathing Thoracic cavity expands & air is forced into nose. Muscles relax & thoracic cavity gets smaller and air is forced out of nose.

  13. Chapter 42: Gas Exchange • Why is gas exchange important? • How have gas exchange systems changed as animals evolved? • How have fish gills evolved for maximal gas exchange? • Why don’t gills work on land? • What adaptations do land animals have? • What is the flow of air in our respiratory system? • What is the difference between positive & negative breathing? • How is breathing controlled? (oxygen homeostasis) • Medulla oblongata & pons • O2 sensors in aorta & carotids & CO2 sensors in carotids

  14. Cerebrospinalfluid The control center in the medulla sets the basicrhythm, and a control centerin the pons moderates it,smoothing out thetransitions between inhalations and exhalations. 4 1 5 2 Carotidarteries Aorta 3 6 Figure 42.26 Automatic control of breathing The medulla’s control center alsohelps regulate blood CO2 level. Sensorsin the medulla detect changes in the pH (reflecting CO2 concentration) of the blood and cerebrospinal fluid bathing the surface of the brain. Nerve impulses relay changes in CO2 and O2 concentrations. Other sensors in the walls of the aortaand carotid arteries in the neck detect changes in blood pH andsend nerve impulses to the medulla. In response, the medulla’s breathingcontrol center alters the rate anddepth of breathing, increasing bothto dispose of excess CO2 or decreasingboth if CO2 levels are depressed. Pons Nerve impulses trigger muscle contraction. Nervesfrom a breathing control centerin the medulla oblongata of the brain send impulses to thediaphragm and rib muscles, stimulating them to contractand causing inhalation. Breathing control centers Medullaoblongata In a person at rest, these nerve impulses result in about 10 to 14 inhalationsper minute. Between inhalations, the musclesrelax and the person exhales. The sensors in the aorta andcarotid arteries also detect changesin O2 levels in the blood and signal the medulla to increase the breathing rate when levels become very low. Diaphragm Rib muscles

  15. Chapter 42: Gas Exchange • Why is gas exchange important? • How have gas exchange systems changed as animals evolved? • How have fish gills evolved for maximal gas exchange? • Why don’t gills work on land? • What adaptations do land animals have? • What is the flow of air in our respiratory system? • What is the difference between positive & negative breathing? • How is breathing controlled? (oxygen homeostasis) • How are gases exchanged across selectively permeable membranes? • - Simple diffusion

  16. Inhaled air Exhaled air 120 27 160 0.2 Alveolar spaces O2 CO2 O2 CO2 Alveolarepithelialcells 104 40 O2 CO2 O2 CO2 Blood leaving alveolar capillaries Blood enteringalveolarcapillaries O2 CO2 3 1 2 4 Alveolar capillariesof lung 40 45 104 40 O2 O2 CO2 CO2 Pulmonaryveins Pulmonaryarteries Systemic arteries Systemicveins Heart Tissue capillaries O2 CO2 Blood enteringtissuecapillaries Blood leavingtissuecapillaries O2 CO2 100 40 40 45 O2 O2 CO2 CO2 Tissue cells <40 >45 O2 CO2 Figure 42.27 Loading and unloading of respiratory gases

  17. Chapter 42: Gas Exchange • Why is gas exchange important? • How have gas exchange systems changed as animals evolved? • How have fish gills evolved for maximal gas exchange? • Why don’t gills work on land? • What adaptations do land animals have? • What is the flow of air in our respiratory system? • What is the difference between positive & negative breathing? • How is breathing controlled? (oxygen homeostasis) • How are gases exchanged? • How is the O2 carried in the blood? • - By hemoglobin in RBCs

  18. Heme group Iron atom O2 loaded in lungs O2 O2 unloaded In tissues O2 Polypeptide chain Figure 42.28 Hemoglobin loading and unloading O2 Cooperativity works in loading & unloading of O2. RBC do not have a nucleus so more room for Hb. 1 RBC has 250 million Hb molecules X 4 O2 molecules = 1 billion O2 per RBC X 25 trillion RBC per person = 1 billion O2 per RBC 2.5 x 1022 O2 total

  19. Chapter 42: Gas Exchange • Why is gas exchange important? • How have gas exchange systems changed as animals evolved? • How have fish gills evolved for maximal gas exchange? • Why don’t gills work on land? • What adaptations do land animals have? • What is the flow of air in our respiratory system? • What is the difference between positive & negative breathing? • How is breathing controlled? (oxygen homeostasis) • How are gases exchanged? • How is the O2 carried in the blood? • How is O2 dumped from hemoglobin?

  20. O2 unloaded from hemoglobin during normal metabolism (a) PO2 and Hemoglobin Dissociation at 37°C and ph 7.4 100 80 O2 reserve that can be unloaded from hemoglobin to tissues with high metabolism 60 O2 saturation of hemoglobin (%) 40 20 0 60 100 40 80 0 20 Tissues at rest Lungs Tissues during exercise PO2 (mm Hg) (b) pH and Hemoglobin Dissociation 100 pH 7.4 80 Bohr shift:Additional O2released from hemoglobin at lower pH(higher CO2concentration) 60 O2 saturation of hemoglobin (%) pH 7.2 40 20 0 60 100 40 80 0 20 PO2 (mm Hg) Figure 42.29 Dissociation curves for hemoglobin

  21. Chapter 42: Gas Exchange • Why is gas exchange important? • How have gas exchange systems changed as animals evolved? • How have fish gills evolved for maximal gas exchange? • Why don’t gills work on land? • What adaptations do land animals have? • What is the flow of air in our respiratory system? • What is the difference between positive & negative breathing? • How is breathing controlled? (oxygen homeostasis) • How are gases exchanged? • How is the O2 carried in the blood? • How is O2 dumped from hemoglobin? • How does CO2 travel from tissues to lungs? • - Most dissolved in plasma as bicarbonate ion

  22. Tissue cell Carbon dioxide produced bybody tissues diffuses into the interstitial fluid and the plasma. Most of the HCO3– diffuseinto the plasma where it is carried in the bloodstream to the lungs. CO2 transportfrom tissues 11 10 7 6 5 4 3 2 1 8 9 CO2 produced Interstitialfluid CO2 Over 90% of the CO2 diffuses into red blood cells, leaving only 7%in the plasma as dissolved CO2. Blood plasmawithin capillary CO2 Capillarywall In the HCO3– diffusefrom the plasma red blood cells, combining with H+ released from hemoglobin and forming H2CO3. CO2 H2O Some CO2 is picked up and transported by hemoglobin. Redbloodcell Hemoglobinpicks upCO2 and H+ H2CO3 Hb Carbonic acid Carbonic acid is converted back into CO2 and water. HCO3– + H+ Bicarbonate However, most CO2 reacts with water in red blood cells, forming carbonic acid (H2CO3), a reaction catalyzed bycarbonic anhydrase contained. Withinred blood cells. HCO3– To lungs CO2 formed from H2CO3 is unloadedfrom hemoglobin and diffuses into the interstitial fluid. CO2 transportto lungs HCO3– 9 6 2 7 5 4 3 1 8 + H+ HCO3– CO2 diffuses into the alveolarspace, from which it is expelledduring exhalation. The reductionof CO2 concentration in the plasmadrives the breakdown of H2CO3 Into CO2 and water in the red bloodcells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4). Carbonic acid dissociates into a biocarbonate ion (HCO3–) and a hydrogen ion (H+). HemoglobinreleasesCO2 and H+ Hb H2CO3 H2O CO2 Hemoglobin binds most of the H+ from H2CO3 preventing the H+from acidifying the blood and thuspreventing the Bohr shift. CO2 11 10 CO2 CO2 Alveolar space in lung Figure 42.30 Carbon dioxide transport in the blood

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