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MECHANISMS OF GAS EXCHANGE Copyright © 2009 Pearson Education, Inc. Introduction: Surviving in Thin Air The process of gas exchange is called respiration, the interchange of – O2 and the waste product CO2 – Between an organism and its environment Copyright © 2009 Pearson Education, Inc. 22.1 Overview: Gas exchange in an animal with lungs involves breathing, transport of gases, and exchange of gases with tissue cells Three phases of gas exchange – Breathing – Transport of oxygen and carbon dioxide in blood – Body tissues take up oxygen and release carbon dioxide Cellular respiration requires a continuous supply of oxygen and the disposal of carbon dioxide Copyright © 2009 Pearson Education, Inc. O2 1 Breathing CO2 Lung Circulatory system 2 Transport of gases by the circulatory system Mitochondria 3 Exchange of gases with body cells O2 CO2 Capillary Cell 22.2 Animals exchange O2 and CO2 across moist body surfaces Respiratory surfaces must be thin and moist for diffusion of O2 and CO2 Earthworms and other animals use their skin for gas exchange Copyright © 2009 Pearson Education, Inc. Cut Cross section of respiratory surface (the outer skin) CO2 O2 Capillaries 22.2 Animals exchange O2 and CO2 across moist body surfaces Most animals have specialized body parts that promote gas exchange – Gills in fish and amphibians – Tracheal systems in arthropods – Lungs in tetrapods that live on land – Amphibians – Reptiles – Birds – Mammals Copyright © 2009 Pearson Education, Inc. Body surface Respiratory surface (gill) CO2 O2 Capillary Body surface Respiratory surface (air tubes) O2 CO2 Body cells (no capillaries) Body surface CO2 CO2 O2 Respiratory surface (within lung) O2 Capillary 22.3 Gills are adapted for gas exchange in aquatic environments Gills – Are extensions of the body – Increase the surface to volume ratio – Increase the surface area for gas exchange – Oxygen absorbed – Carbon dioxide released Copyright © 2009 Pearson Education, Inc. 22.3 Gills are adapted for gas exchange in aquatic environments In a fish, gas exchange is enhanced by – Ventilation of the gills (moving water past the gills) – Countercurrent flow of water and blood Copyright © 2009 Pearson Education, Inc. 22.3 Gills are adapted for gas exchange in aquatic environments Cold water holds more oxygen than warm water Fresh water holds more oxygen than salt water Turbulent water holds more oxygen than still water Copyright © 2009 Pearson Education, Inc. Gill arch Gill Oxygen-poor blood Direction arch of water Direction flow Lamella Oxygen-rich blood of water flow Gill arch Gill Blood vessels arch Blood vessels Operculum Operculum (gill cover) Water flow between lamellae (gill cover) Gill filaments Blood flow through capillaries in lamella Countercurrent exchange Water flow, showing % O2 Diffusion of O2 from water to blood Gill 15 filaments 100 70 40 80 30 60 5 Blood flow in simplified capillary, showing % O2 Oxygen-poor blood Lamella Oxygen-rich blood Gill arch Blood vessels Water flow between lamellae Gill filaments Blood flow through capillaries in lamella Countercurrent exchange Water flow, showing % O2 100 70 Diffusion of O2 from water to blood 80 40 15 60 30 5 Blood flow in simplified capillary, showing % O2 22.4 The tracheal system of insects provides direct exchange between the air and body cells Compared to water, using air to breathe has two big advantages – Air contains higher concentrations of O2 – Air is lighter and easier to move Copyright © 2009 Pearson Education, Inc. Air sacs Tracheae Opening for air Body cell Tracheole Air sac Trachea O2 CO2 Body wall 22.5 EVOLUTION CONNECTION: The evolution of lungs facilitated the movement of tetrapods onto land Tetrapods seem to have evolved in shallow water – Fossil fish with legs had lungs and gills – Legs may have helped them lift up to gulp air – The fossil fish Tiktaalik illustrates these air-breathing adaptations Copyright © 2009 Pearson Education, Inc. 22.5 EVOLUTION CONNECTION: The evolution of lungs facilitated the movement of tetrapods onto land The first tetrapods on land diverged into three major lineages – Amphibians use small lungs and their body surfaces – Nonbird reptiles have lower metabolic rates and simpler lungs – Birds and mammals have higher metabolic rates and more complex lungs Copyright © 2009 Pearson Education, Inc. 22.6 In the human respiratory system, branching tubes convey air to lungs located in the chest cavity In mammals, air is inhaled through the nostrils into the nasal cavity – Air is filtered by hairs and mucus surfaces – Air is warmed and moisturized – Air is sampled for odors Copyright © 2009 Pearson Education, Inc. 22.6 In the human respiratory system, branching tubes convey air to lungs located in the chest cavity From the nasal cavity, air next passes – To the pharynx – Then larynx, past the vocal cords – Into the trachea, held open by cartilage rings – Into the paired bronchi – Into bronchioles – And finally to the alveoli, grapelike clusters of air sacs, where gas exchange occurs Copyright © 2009 Pearson Education, Inc. Oxygen-rich blood Nasal cavity Pharynx Larynx (Esophagus) Oxygen-poor blood Bronchiole Alveoli Left lung Trachea Right lung Bronchus Blood capillaries Bronchiole Diaphragm (Heart) 22.6 In the human respiratory system, branching tubes convey air to lungs located in the chest cavity Alveoli are well adapted for gas exchange – High surface area of capillaries – High surface area of alveoli In alveoli – O2 diffuses into the blood – CO2 diffuses out of the blood Copyright © 2009 Pearson Education, Inc. 22.7 CONNECTION: Smoking is a serious assault on the respiratory system Mucus and cilia in the respiratory passages – Protect the lungs – Can be damaged by smoking Without healthy cilia, smokers must cough to clear dirty mucus from the trachea Copyright © 2009 Pearson Education, Inc. 22.7 CONNECTION: Smoking is a serious assault on the respiratory system Smoking can cause – Lung cancer – Heart disease – Emphysema Smoking accounts for 90% of all lung cancer cases Smoking increases the risk of other types of cancer Copyright © 2009 Pearson Education, Inc. 22.7 CONNECTION: Smoking is a serious assault on the respiratory system Smoking also – Increases the risk of heart attacks and strokes – Raises blood pressure – Increases harmful types of cholesterol Every year in the United States, smoking kills about 440,000 people – This is more than all the deaths from accidents, alcohol, drug abuse, HIV, and murders combined Adults who smoke cut 13–14 years from their lifespan Copyright © 2009 Pearson Education, Inc. Lung Heart 22.8 Negative pressure breathing ventilates our lungs Breathing is the alternate inhalation and exhalation of air (ventilation) Inhalation occurs when – The rib cage expands – The diaphragm moves downward – The pressure around the lungs decreases – And air is drawn into the respiratory tract Copyright © 2009 Pearson Education, Inc. 22.8 Negative pressure breathing ventilates our lungs Exhalation occurs when – The rib cage contracts – The diaphragm moves upward – The pressure around the lungs increases – And air is forced out of the respiratory tract Copyright © 2009 Pearson Education, Inc. Rib cage gets Rib cage expands as rib muscles contract Air inhaled smaller as rib muscles relax Air exhaled Lung Diaphragm Diaphragm contracts (moves down) Diaphragm relaxes (moves up) Inhalation Exhalation 22.8 Negative pressure breathing ventilates our lungs Not all air is expelled during exhalation – Some air still remains in the trachea, bronchi, bronchioles, and alveoli – This remaining air is “dead air” – Thus, inhalation mixes fresh air with dead air One-way flow of air in birds reduces dead air and increases their ability to obtain oxygen Copyright © 2009 Pearson Education, Inc. 22.9 Breathing is automatically controlled Breathing is usually under automatic control Breathing control centers in the brain sense and respond to CO2 levels in the blood A drop in blood pH increases the rate and depth of breathing Copyright © 2009 Pearson Education, Inc. Cerebrospinal fluid Brain Pons 1 Nerve signals trigger contraction of muscles Diaphragm Rib muscles Medulla Cerebrospinal fluid Brain Pons 2 Breathing control 1 Nerve signals trigger contraction of muscles Diaphragm Rib muscles Medulla centers respond to pH of blood Cerebrospinal fluid Brain Pons 2 Breathing control 1 Nerve signals trigger contraction of muscles Medulla centers respond to pH of blood 3 Nerve signals indicating CO2 and O2 levels CO2 and O2 sensors in aorta Diaphragm Rib muscles TRANSPORT OF GASES IN THE HUMAN BODY Copyright © 2009 Pearson Education, Inc. 22.10 Blood transports respiratory gases The heart pumps blood to two regions – The right side pumps oxygen-poor blood to the lungs – The left side pumps oxygen-rich blood to the body In the lungs, blood picks up O2 and drops off CO2 In the body tissues, blood drops off O2 and picks up CO2 Copyright © 2009 Pearson Education, Inc. 22.10 Blood transports respiratory gases Gases move from areas of higher concentration to areas of lower concentration – Gases in the alveoli of the lungs have more O2 and less CO2 than gases the blood – O2 moves from the alveoli of the lungs into the blood – CO2 moves from the blood into the alveoli of the lungs – The tissues have more CO2 and less O2 than in the blood – CO2 moves from the tissues into the blood – O2 moves from the blood into the tissues Copyright © 2009 Pearson Education, Inc. 22.10 Blood transports respiratory gases Animation: CO2 from Blood to Lungs Animation: CO2 from Tissues to Blood Animation: O2 from Blood to Tissues Animation: O2 from Lungs to Blood Copyright © 2009 Pearson Education, Inc. Inhaled air Exhaled air Alveolar epithelial cells Air spaces CO2 O2 Alveolar capillaries CO2-rich, O2-poor blood O2-rich, CO2-poor blood Heart Tissue capillaries CO2 Tissue cells throughout body O2 Interstitial fluid 22.11 Hemoglobin carries O2, helps transport CO2, and buffers the blood Most animals transport O2 bound to proteins called respiratory pigments – Copper-containing pigment is used by – Molluscs – Arthropods – Iron-containing hemoglobin – Is used by almost all vertebrates and many invertebrates – Transports oxygen, buffers blood, and transports CO2 Copyright © 2009 Pearson Education, Inc. Iron atom O2 loaded in lungs O2 unloaded in tissues Heme group Polypeptide chain O2 O2 22.11 Hemoglobin carries O2, helps transport CO2, and buffers the blood Most CO2 in the blood is transported as bicarbonate ions in the plasma Copyright © 2009 Pearson Education, Inc. 22.11 Hemoglobin carries O2, helps transport CO2, and buffers the blood CO2 + H2O Carbon Dioxide Water Copyright © 2009 Pearson Education, Inc. H2CO3 Carbonic Acid H+ + HCO3Hydrogen Ions Bicarbonate 22.12 CONNECTION: The human fetus exchanges gases with the mother’s bloodstream A human fetus – Does not breathe with its lungs – Instead, it exchanges gases with maternal blood in the placenta In the placenta, capillaries of maternal blood and fetal blood run next to each other – The fetus and mother do not share the same blood Copyright © 2009 Pearson Education, Inc. 22.12 CONNECTION: The human fetus exchanges gases with the mother’s bloodstream Fetal hemoglobin – Attracts O2 more strongly than adult hemoglobin – Thus, fetal blood takes oxygen from maternal blood At birth – CO2 in fetal blood increases – Breathing control centers initiate breathing Copyright © 2009 Pearson Education, Inc. Placenta, containing maternal blood vessels and fetal capillaries Umbilical cord, containing fetal blood vessels Amniotic fluid Uterus Introduction: Surviving in Thin Air People cannot survive in the air at the world’s highest peaks in the Himalayan Mountains Twice a year, flocks of geese migrate over the Himalayas How can geese fly where people cannot breathe? – Geese have more efficient lungs than humans – Geese hemoglobin has a very high affinity for oxygen Copyright © 2009 Pearson Education, Inc. 100 Llama 80 Human 60 40 20 0 0 20 40 60 PO (mm Hg) 2 80 100 You should now be able to 1. Explain how geese can fly at altitudes higher than Mount Everest 2. Describe the three main phases of gas exchange in a human 3. Describe four types of respiratory surfaces and the types of animals that use them 4. Explain how breathing air compares to using water for gas exchange Copyright © 2009 Pearson Education, Inc. You should now be able to 5. Describe the parts and functions of the human respiratory system 6. Describe the impact of smoking on human health 7. Explain how blood transports gases between the lungs and tissues of the body 8. Describe the functions of hemoglobin 9. Explain how a fetus obtains oxygen before and after birth Copyright © 2009 Pearson Education, Inc. Lamella Water flow Blood flow Gas exchange requires moist, thin often relies on (b) (a) for exchange of O2 to transport gases between red blood cells contain CO2 (c) (d) needed waste for product of mammals ventilate by (e) binds and transports and helps to (f) tissue cells regulated by breathing control centers transport CO2 and buffer the blood (g) a. b. c. d. e. f. g. h.