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Chapter 22

Chapter 22. Gas Exchange. Surviving in Thin Air The air at the height of Mt. Everest is so low in oxygen that most people would pass out instantly if exposed to it Geese that migrate over high mountains have adaptations for using and storing oxygen efficiently

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Chapter 22

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  1. Chapter 22 Gas Exchange

  2. Surviving in Thin Air • The air at the height of Mt. Everest is so low in oxygen that most people would pass out instantly if exposed to it • Geese that migrate over high mountains have adaptations for using and storing oxygen efficiently • Humans living at extremely high altitudes have adapted to function with relatively little oxygen • Gas exchange is the interchange of O2 and the waste product CO2 between an animal and its environment

  3. MECHANISMS OF GAS EXCHANGE • 22.1 Overview: Gas exchange involves breathing, transport of gases, and exchange of gases with tissue cells • Gas exchange provides O2 for cellular respiration and removes its waste product, CO2 • Involves respiratory and circulatory systems • Gas exchange has three phases 1. Breathing • O2 is taken into lungs and blood vessels • CO2 diffuses out and leaves body

  4. 2. Transport of gases by the circulatory system • O2 attaches to hemoglobin and is carried in blood to body tissues • CO2 is transported from tissues back to lungs 3. Body cells take up O2 from blood and release CO2 back to the blood

  5. LE 22-1 O2 Breathing CO2 Lung Circulatory system Transport of gases by the circulatory system Mitochondria O2 Exchange of gases with body cells CO2 Capillary Cell

  6. 22.2 Animals exchange O2 and CO2 across moist body surfaces • For diffusion of O2 and CO2 to occur in both aquatic and terrestrial animals • Respiratory surfaces must be thin and moist • Gases must be dissolved in water

  7. Gas exchange occurs in four types of respiratory organs • Entire outer skin: animals living in moist environments • Gills: most aquatic animals • Tracheal system: insects • Lungs: most terrestrial vertebrates

  8. LE 22-2a Cut Cross section of respiratory surface (the skin covering the body) CO2 Capillaries O2

  9. LE 22-2b Body surface Respiratory surface (gill) Capillary CO2 O2

  10. LE 22-2c Body surface Respiratory surface (air tubes) Body cells (no capillaries) O2 CO2

  11. LE 22-2d Body surface Respiratory surface (within lung) O2 CO2 CO2 O2 Capillary

  12. 22.3 Gills are adapted for gas exchange in aquatic environments • Gills are extensions of the body that absorb O2 dissolved in water • Found in fishes and many invertebrates • Are among the most efficient gas exchange organs in the aquatic world • Ventilation increases the flow of the surrounding water over the respiratory surface • Requires considerable energy from fish

  13. Arrangement of capillaries in a fish gill enhances gas exchange • Blood flows in a direction opposite to water flow • Countercurrent exchange • Transfers something from a fluid moving in one direction to another fluid moving in the opposite direction • Enables gills to remove more than 80% of the O2 in the water flowing past them

  14. LE 22-3 Gill arch Oxygen-poor blood Direction of water flow Lamella Oxygen-rich blood Gill arch 15% 40% 70% O2 30% 5% 60% 100% Blood vessels 80% % O2 in water flowing over lamellae % O2 in blood flowing through capillaries in lamellae Gill filaments Countercurrent exchange

  15. 22.4 The tracheal system of insects provides direct exchange between the air and body cells • Advantages to exchanging gases by breathing air • Air contains a high concentration of O2 • Air is lighter and easier to move than water • Main problem with breathing air: loss of water to air by evaporation

  16. Tracheal systems in insects • Transport O2 directly to cells through a network of finely branched tubes throughout the body • In small insects, diffusion is sufficient to exchange gases • Large insects may ventilate the tracheal system with rhythmic body movements • In many insects, contraction and relaxation of flight muscles pumps air through the tracheal system

  17. LE 22-4a Air sacs Tracheae Opening for air Body cell Air sac Tracheole LM 250 Trachea Body wall CO2 O2

  18. 22.5 Terrestrial vertebrates have lungs • Amphibians have small lungs and rely heavily on diffusion of gases across body surfaces • Most reptiles (including birds) and mammals rely exclusively on lungs • Size and complexity of lungs are correlated with metabolic rate • Lungs are restricted to one location in the body • Circulatory system must transport gases between lungs and rest of body

  19. Pathway of air in mammals • Inhaled through the nostrils • Passes through the pharynx and larynx (including vocal cords) • Into the trachea, bronchi, and bronchioles • Bronchioles end in clusters of tiny alveoli,where gas exchange occurs • Cilia and mucus are the respiratory system's cleaning elements

  20. LE 22-5b Oxygen-poor blood Oxygen-rich blood Bronchiole Alveoli Blood capillaries

  21. CONNECTION • 22.6 Smoking is a deadly assault on our respiratory system • Tobacco smoke irritates cells lining the bronchi • Inhibits or destroys cilia • Kills defensive macrophages • Smoking causes lung cancer, emphysema, and cardiovascular disease • Choosing not to smoke is the most important lifestyle choice for health

  22. LE 22-6 Lung Heart

  23. 22.7 Breathing ventilates the lungs • Breathing is the alternation of inhalation and exhalation • Maintains high O2 and low CO2 at the respiratory surface • Negative pressure breathing • During inhalation, changes in lungs, diaphragm, and rib cage reduce air pressure in alveoli • Air rushes in due to higher pressure outside

  24. During exhalation, decreased volume of chest cavity forces air out • Vital capacity is the maximum volume of air we can inhale and exhale during forced breathing • A residual volume of air ("dead air") remains in lungs even after exhalation

  25. LE 22-7a Rib cage gets smaller as rib muscles relax Rib cage expands as rib muscles contract Air inhaled Air exhaled Lung Diaphragm Diaphragm contracts (moves down) Diaphragm relaxes (moves up) Inhalation Exhalation

  26. Birds have a one-way flow of air through the lungs • Several large sacs act as bellows to keep air flowing • Tiny parallel tubes, not alveoli, function in gas exchange • No residual volume, so lung oxygen concentrations are higher in birds than in humans

  27. LE 22-7b Air Air Anterior air sacs Trachea Posterior air sacs Lungs Air tubes in lung SEM 9 Inhalation: Air sacs fill Exhalation: Air sacs empty; lungs fill

  28. 22.8 Breathing is automatically controlled • Breathing control centers in the brain signal diaphragm and rib muscles to contract about 10-14 times a minute • Control centers adjust breathing rate to respond to body's needs by monitoring CO2 level in the blood • High CO2 results in a drop in blood pH • Low pH triggers an increase in the rate and depth of breathing, bringing in more O2 • Response to O2 level is thus indirect

  29. Hyperventilation purges blood of so much CO2 that control centers cease to send signals and breathing stops • Secondary control over breathing is exerted by sensors in the aorta and carotid arteries • Monitor concentrations of O2 and CO2 • Signal control centers in brain to increase rate of breathing when O2 is low • Breathing rate must be coordinated with activity of the circulatory system

  30. LE 22-8-2 Brain Cerebrospinal fluid Pons Breathing control centers stimulated by: Medulla CO2 increase/pH decrease in blood Nerve signals indicating CO2 and O2 levels Nerve signals trigger contraction of muscles CO2 and O2 sensors in aorta Diaphragm Rib muscles

  31. TRANSPORT OF GASES IN THE BODY • 22.9 Blood transports respiratory gases • One side of the heart pumps O2-poor, CO2-rich blood from the body to the lungs • The other side of the heart pumps O2-rich, CO2-poor blood from the lungs to the rest of the body • Gases are exchanged between capillaries and cells • Each kind of gas accounts for a partial pressure of the air mixture • Molecules of each kind of gas diffuse down a gradient of the gas's partial pressure, independent of other gases

  32. LE 22-9 Exhaled air Inhaled air Alveolar epithelial cells Air spaces O2 CO2 Alveolar capillaries of lung O2-rich, CO2-poor blood CO2-rich, O2-poor blood Heart Tissue capillaries CO2 O2 Interstitial fluid O2 CO2 Tissue cells throughout body

  33. 22.10 Hemoglobin carries O2 and helps transport CO2 and buffer the blood • Most of the O2 in blood is carried by hemoglobin in red blood cells • Each hemoglobin molecule can carry up to four oxygen molecules • Loads up with O2 in lungs, transports it to tissues, unloads some or all depending on needs of cells • Hemoglobin also helps blood transport CO2 and assists in preventing harmful changes in pH

  34. LE 22-10 Iron atom O2 loaded in lungs O2 O2 unloaded in tissues O2 Heme group Polypeptide chain

  35. Animation: O2 From Blood to Tissues Animation: CO2 From Tissues to Blood Animation: CO2 From Blood to Lungs Animation: O2 From Lungs to Blood

  36. CONNECTION • 22.11 The human fetus exchanges gases with the mother's bloodstream • A human fetus exchanges gases with the outside world through the placenta • Fetal capillaries exchange gases with maternal blood that circulates in the placenta • Maternal circulatory system carries the gases to and from the mother's lungs • O2 uptake is aided by fetal hemoglobin, which attracts O2 strongly

  37. When a baby is born, CO2 stops diffusing from the fetus into the placenta • Increased blood CO2 stimulates the infant's breathing control centers to initiate breathing

  38. LE 22-11 Placenta, containing maternal blood vessels and fetal capillaries Umbilical cord, containing fetal blood vessels Amniotic fluid Uterus

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