Copyright © 2009 Pearson Education, Inc. MECHANISMS OF GAS EXCHANGE

Copyright © 2009 Pearson Education, Inc.  The process of gas exchange is called respiration, the interchange of –O 2 and the waste product CO 2 –Between an organism and its environment Introduction: Surviving in Thin Air

Copyright © 2009 Pearson Education, Inc 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

Lung Exchange of gases with body cells Cell Capillary Mitochondria Breathing Circulatory system Transport of gases by the circulatory system CO 2 O2O2 O2O

Copyright © 2009 Pearson Education, Inc Animals exchange O 2 and CO 2 across moist body surfaces  Respiratory surfaces must be thin and moist for diffusion of O 2 and CO 2  Earthworms and other animals use their skin for gas exchange

Cut CO 2 O2O2 Cross section of respiratory surface (the outer skin) Capillaries

Copyright © 2009 Pearson Education, Inc Animals exchange O 2 and CO 2 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

CO 2 O2O2 Capillary Body surface Respiratory surface (gill)

CO 2 O2O2 Body surface Body cells (no capillaries) Respiratory surface (air tubes)

CO 2 O2O2 Body surface Capillary Respiratory surface (within lung) O2O2 CO 2

Copyright © 2009 Pearson Education, Inc 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 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 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

Gill arch Direction of water flow Operculum (gill cover) Gill arch Blood vessels Oxygen-rich blood Oxygen-poor blood Lamella Gill filaments Water flow between lamellae Blood flow through capillaries in lamella Countercurrent exchange Blood flow in simplified capillary, showing % O 2 Diffusion of O 2 from water to blood Water flow, showing % O Gill arch Direction of water flow Operculum (gill cover) Gill arch Blood vessels Gill filaments

Gill arch Blood vessels Oxygen-rich blood Oxygen-poor blood Lamella Gill filaments Water flow between lamellae Blood flow through capillaries in lamella Countercurrent exchange Blood flow in simplified capillary, showing % O 2 Diffusion of O 2 from water to blood Water flow, showing % O

Copyright © 2009 Pearson Education, Inc 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 O 2 –Air is lighter and easier to move

Tracheae Air sacs Opening for air Body cell Tracheole Air sac Trachea Body wall CO 2 O2O2

Copyright © 2009 Pearson Education, Inc 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 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 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 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

Oxygen-rich blood Bronchiole Alveoli Oxygen-poor blood Blood capillaries Nasal cavity Left lung Pharynx Larynx Trachea Right lung Bronchus Bronchiole Diaphragm (Heart) (Esophagus)

Copyright © 2009 Pearson Education, Inc 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 – O 2 diffuses into the blood – CO 2 diffuses out of the blood

Copyright © 2009 Pearson Education, Inc 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 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 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

Lung Heart

Copyright © 2009 Pearson Education, Inc 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 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

Lung Diaphragm contracts (moves down) Diaphragm relaxes (moves up) Diaphragm InhalationExhalation Air inhaled Air exhaled Rib cage expands as rib muscles contract Rib cage gets smaller as rib muscles relax

Copyright © 2009 Pearson Education, Inc 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 Breathing is automatically controlled  Breathing is usually under automatic control  Breathing control centers in the brain sense and respond to CO 2 levels in the blood  A drop in blood pH increases the rate and depth of breathing

Cerebrospinal fluid Pons Medulla Brain Nerve signals trigger contraction of muscles Diaphragm Rib muscles 1

Cerebrospinal fluid Pons Medulla Brain Nerve signals trigger contraction of muscles Diaphragm Rib muscles 1 Breathing control centers respond to pH of blood 2

Cerebrospinal fluid Pons Medulla Brain Nerve signals trigger contraction of muscles Diaphragm Rib muscles 1 Breathing control centers respond to pH of blood 2 Nerve signals indicating CO 2 and O 2 levels 3 CO 2 and O 2 sensors in aorta

Copyright © 2009 Pearson Education, Inc. TRANSPORT OF GASES IN THE HUMAN BODY

Copyright © 2009 Pearson Education, Inc 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 O 2 and drops off CO 2  In the body tissues, blood drops off O 2 and picks up CO 2

Copyright © 2009 Pearson Education, Inc 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 O 2 and less CO 2 than gases the blood –O 2 moves from the alveoli of the lungs into the blood –CO 2 moves from the blood into the alveoli of the lungs –The tissues have more CO 2 and less O 2 than in the blood –CO 2 moves from the tissues into the blood –O 2 moves from the blood into the tissues

Copyright © 2009 Pearson Education, Inc Blood transports respiratory gases Animation: CO 2 from Blood to Lungs Animation: CO 2 from Tissues to Blood Animation: O 2 from Blood to Tissues Animation: O 2 from Lungs to Blood

Alveolar epithelial cells CO 2 O2O2 CO 2 -rich, O 2 -poor blood O 2 -rich, CO 2 -poor blood Exhaled air Inhaled air Air spaces Alveolar capillaries Tissue capillaries Tissue cells throughout body Interstitial fluid Heart CO 2 O2O2 O2O2 O2O2

Copyright © 2009 Pearson Education, Inc Hemoglobin carries O 2, helps transport CO 2, and buffers the blood  Most animals transport O 2 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 CO 2

O 2 loaded in lungs O 2 unloaded in tissues Iron atom Polypeptide chain Heme group O2O2 O2O2

Copyright © 2009 Pearson Education, Inc Hemoglobin carries O 2, helps transport CO 2, and buffers the blood  Most CO 2 in the blood is transported as bicarbonate ions in the plasma

Copyright © 2009 Pearson Education, Inc Hemoglobin carries O 2, helps transport CO 2, and buffers the blood

Copyright © 2009 Pearson Education, Inc 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 CONNECTION: The human fetus exchanges gases with the mother’s bloodstream  Fetal hemoglobin –Attracts O 2 more strongly than adult hemoglobin –Thus, fetal blood takes oxygen from maternal blood  At birth –CO 2 in fetal blood increases –Breathing control centers initiate breathing

Amniotic fluid Uterus Umbilical cord, containing fetal blood vessels Placenta, containing maternal blood vessels and fetal capillaries

Copyright © 2009 Pearson Education, Inc. 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

P Llama Human O2O2 (mm Hg) O 2 saturation of hemoglobin (%)

Copyright © 2009 Pearson Education, Inc. 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

Blood flow Water flow Lamella

transport CO 2 and buffer the blood tissue cells regulated by breathing control centers mammals ventilate by helps to and binds and transports to transport gases between red blood cells contain Gas exchange requires moist, thin often relies on for exchange of needed for waste product of CO 2 O2O2 (e) (d) (c) (b) (a) (g)(f)

a. b. c. d. e. g. f. h.