Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Chapter 22 Gas Exchange

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 O 2 and the waste product CO 2 between an animal and its environment

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings MECHANISMS OF GAS EXCHANGE 22.1 Overview: Gas exchange involves breathing, transport of gases, and exchange of gases with tissue cells Gas exchange provides O 2 for cellular respiration and removes its waste product, CO 2 – Involves respiratory and circulatory systems Gas exchange has three phases 1. Breathing O 2 is taken into lungs and blood vessels CO 2 diffuses out and leaves body

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2. Transport of gases by the circulatory system O 2 attaches to hemoglobin and is carried in blood to body tissues CO 2 is transported from tissues back to lungs 3. Body cells take up O 2 from blood and release CO 2 back to the blood

LE 22-1 Lung Breathing O2O2 CO 2 Circulatory system Transport of gases by the circulatory system Mitochondria CO 2 O2O2 Capillary Cell Exchange of gases with body cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 22.2 Animals exchange O 2 and CO 2 across moist body surfaces For diffusion of O 2 and CO 2 to occur in both aquatic and terrestrial animals – Respiratory surfaces must be thin and moist – Gases must be dissolved in water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

LE 22-2a Cut Cross section of respiratory surface (the skin covering the body) Capillaries CO 2 O2O2

LE 22-2b Body surface Respiratory surface (gill) Capillary CO 2 O2O2

LE 22-2c Body surface Respiratory surface (air tubes) Body cells (no capillaries) O2O2 CO 2

LE 22-2d Body surface Capillary O2O2 CO 2 Respiratory surface (within lung) CO 2 O2O2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 22.3 Gills are adapted for gas exchange in aquatic environments Gills are extensions of the body that absorb O 2 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 O 2 in the water flowing past them

LE 22-3 Direction of water flow Blood vessels Oxygen-rich blood Gill filaments Gill arch Oxygen-poor blood Lamella Countercurrent exchange % O 2 in blood flowing through capillaries in lamellae % O 2 in water flowing over lamellae 40% 15% 70% 100% 30% 5% 60% 80% O2O2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 O 2 – Air is lighter and easier to move than water Main problem with breathing air: loss of water to air by evaporation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tracheal systems in insects – Transport O 2 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

LE 22-4a Air sacs Opening for air Tracheae Body cell LM 250  Tracheole Air sac Trachea Body wall O2O2 CO 2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

LE 22-6 Lung Heart

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 22.7 Breathing ventilates the lungs Breathing is the alternation of inhalation and exhalation – Maintains high O 2 and low CO 2 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – 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

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 22.8 Breathing is automatically controlled Breathing control centers in the brain signal diaphragm and rib muscles to contract about times a minute Control centers adjust breathing rate to respond to body's needs by monitoring CO 2 level in the blood – High CO 2 results in a drop in blood pH – Low pH triggers an increase in the rate and depth of breathing, bringing in more O 2 – Response to O 2 level is thus indirect

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hyperventilation purges blood of so much CO 2 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 O 2 and CO 2 – Signal control centers in brain to increase rate of breathing when O 2 is low Breathing rate must be coordinated with activity of the circulatory system

LE Pons Medulla Brain Cerebrospinal fluid Breathing control centers stimulated by: CO 2 increase/pH decrease in blood Nerve signals indicating CO 2 and O 2 levels CO 2 and O 2 sensors in aorta Nerve signals trigger contraction of muscles Diaphragm Rib muscles

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings TRANSPORT OF GASES IN THE BODY 22.9 Blood transports respiratory gases One side of the heart pumps O 2 -poor, CO 2 -rich blood from the body to the lungs The other side of the heart pumps O 2 -rich, CO 2 -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

LE 22-9 Alveolar epithelial cells Air spaces CO 2 O2O2 Alveolar capillaries of lung CO 2 -rich, O 2 -poor blood O 2 -rich, CO 2 -poor blood Heart Tissue capillaries CO 2 O2O2 O2O2 Interstitial fluid Inhaled airExhaled air Tissue cells throughout body

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hemoglobin carries O 2 and helps transport CO 2 and buffer the blood Most of the O 2 in blood is carried by hemoglobin in red blood cells Each hemoglobin molecule can carry up to four oxygen molecules – Loads up with O 2 in lungs, transports it to tissues, unloads some or all depending on needs of cells Hemoglobin also helps blood transport CO 2 and assists in preventing harmful changes in pH

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: O2 From Blood to Tissues Animation: O2 From Blood to Tissues Animation: CO2 From Tissues to Blood Animation: CO2 From Tissues to Blood Animation: CO2 From Blood to Lungs Animation: CO2 From Blood to Lungs Animation: O2 From Lungs to Blood Animation: O2 From Lungs to Blood

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 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 – O 2 uptake is aided by fetal hemoglobin, which attracts O 2 strongly

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings When a baby is born, CO 2 stops diffusing from the fetus into the placenta – Increased blood CO 2 stimulates the infant's breathing control centers to initiate breathing

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