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BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 22 Respiration: The Exchange of Gases From PowerPoint® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Surviving in Thin Air • The air at the height of the world’s highest peak, Mt. Everest, is very low in oxygen – Even expert mountain climbers do not always survive the journey – Thin air can weaken muscles, damage the digestive system, cloud the mind, and sometimes fill the lungs with blood Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Geese have adaptations that allow them to fly over the Himalayas – Their efficient lungs draw more oxygen from the atmosphere – Their hemoglobin has a high affinity for oxygen – They have a large number of capillaries to deliver this oxygenrich blood to tissues and muscles Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings MECHANISMS OF GAS EXCHANGE • Gas exchange is the interchange of O2 and CO2 between an organism and its environment – It is also called respiration Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 22.1 Overview: Gas exchange involves breathing, the transport of gases, and the servicing of tissue cells • Gas exchange is essential because energy metabolism requires O2 and produces CO2 • There are three phases of gas exchange Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings O2 Lung CO2 1 Breathing Circulatory system 2 Transport of gases by the circulatory system Mitochondria 3 Servicing of O2 cells within the body tissues CO2 Capillary Cell Figure 22.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 22.2 Animals exchange O2 and CO2 through moist body surfaces • O2 enters an animal and CO2 leaves by diffusion through a respiratory surface – Respiratory surfaces are made up of living cells Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Some animals use their entire skin as a gasexchange organ – Example: earthworms Cut Cross section of respiratory surface (the skin covering the body) CO2 O2 Capillaries Figure 22.2A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • In most animals, specialized body parts carry out gas exchange – Gills in fish Body surface Respiratory surface (gill) CO2 Capillaries O2 Figure 22.2B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – Lungs in land vertebrates – Tracheae in insects Body surface Body surface Respiratory surface (tracheae) O2 Body cells (no capillaries) Respiratory surface (within lung) CO2 O2 Capillary CO2 Figure 22.2C, D Copyright © 2003 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 O2 dissolved in water • In fish, gill filaments bear numerous platelike lamellae – Lamellae are packed with blood vessels – They are the respiratory surfaces Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The structure of fish gills Gill arch Direction of water flow Gill arch Blood vessels Oxygen-poor blood Gill filaments Oxygen-rich blood Lamella Water flow Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 22.3 22.4 Countercurrent flow in the gills enhances O2 transfer • Blood flows through the lamellae in a direction opposite to water flow – This countercurrent maintains a diffusion gradient that maximizes the uptake of O2 Water flow over lamellae Blood flow through lamellae Figure 22.4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 22.5 The tracheal system of insects provides direct exchange between the air and body cells • Land animals exchange gases by breathing air – Air contains more O2 and is easier to move than water – But water loss from the respiratory surfaces can be a problem Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • In insects, a network of tracheal tubes carries out gas exchange – O2 diffuses from the finely branched tubes directly into cells Figure 22.5B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Air sacs Tracheae Opening for air Body cell Tracheole Air sac Trachea Air Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Body wall Figure 22.5A, C 22.6 Terrestrial vertebrates have lungs • In humans and other mammals, air enters through the nasal cavity – It passes through the pharynx and larynx into the trachea – The trachea forks to form two bronchi – Each bronchus branches into numerous bronchioles Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The human respiratory system Nasal cavity Pharynx (Esophagus) Left lung Larynx Trachea Right lung Bronchus Bronchiole Diaphragm (Heart) Figure 22.6A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The bronchioles end in clusters of tiny sacs called alveoli – Alveoli form the respiratory surface of the lungs – Oxygen diffuses through the thin walls of the alveoli into the blood Figure 22.6C Oxygen-rich blood Oxygen-poor blood Bronchiole Alveoli Blood capillaries Figure 22.6B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 22.7 Connection: Smoking is one of the deadliest assaults on our respiratory system • Mucus and cilia in the respiratory passages protect the lungs – Pollutants, including tobacco smoke, can destroy these protections • Smoking kills about 430,000 Americans each year Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Smoking causes lung cancer and contributes to heart disease • Smoking also causes emphysema – Cigarette smoke makes alveoli brittle, causing them to rupture – This reduces the lungs’ capacity for gas exchange Figure 22.7A, B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 22.8 Breathing ventilates the lungs • Breathing is the alternation of inhalation and exhalation Rib cage expands as rib muscles contract Air inhaled Rib cage gets smaller as rib muscles relax Air exhaled Lung Diaphragm INHALATION Diaphragm contracts (moves down) EXHALATION Diaphragm relaxes (moves up) Figure 22.8A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Vital capacity is the maximum volume of air we can inhale and exhale – But our lungs hold more than this amount – The alveoli do not completely collapse – A residual volume of “dead” air remains in the lungs after exhalation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Other organisms, such as birds, have air sacs – These structures act as bellows that keep air flowing through the lungs – However, they do not function directly in gas exchange Air Air Anterior air sacs Trachea Posterior air sacs Lungs Lungs Air tubes in lung INHALATION: Air sacs fill Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings EXHALATION: Air sacs empty; lungs fill 1 mn Figure 22.8B 22.9 Breathing is automatically controlled • Breathing control centers are located in the pons and medulla of the brain – These automatic controls keep breathing in tune with body needs Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • During exercise, the CO2 level in the blood rises, lowering the blood pH – This triggers a cascade of events Brain Cerebrospinal fluid BREATHING CONTROL CENTERS—stimulated by: Pons Medulla CO2 increase / pH decrease in blood Nerve signal indicating low O2 level Nerve signals trigger contraction of muscles O2 sensor in artery Diaphragm Figure 22.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Rib muscles TRANSPORT OF GASES IN THE BODY 22.10 Blood transports the respiratory gases, with hemoglobin carrying the oxygen • The heart pumps oxygen-poor blood to the lungs – In the lungs it picks up O2 and drops off CO2 – In the tissues, cells pick up CO2 and drop off O2 – Gases diffuse down pressure gradients in the lungs and the tissues Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Gas exchange in the body Figure 22.10A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Hemoglobin is a protein in red blood cells – It carries most of the oxygen in the blood Heme group Iron atom O2 loaded in lungs O2 unloaded in tissues O2 O2 Polypeptide chain Figure 22.10B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 22.11 Hemoglobin helps transport CO2 and buffer the blood • Hemoglobin helps buffer the pH of blood and carries some CO2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Most CO2 in the blood combines with water to form carbonic acid – The carbonic acid breaks down to form H+ ions and bicarbonate ions – These help buffer the blood TISSUE CELL CO2 produced INTERSTITIAL CO 2 FLUID BLOOD PLASMA WITHIN CAPILLARY CO2 CO2 H2O RED BLOOD CELL H2CO3 Carbonic acid HCO3– + Bicarbonate HCO3– Figure 22.11A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Capillary wall H+ Hemoglobin picks up CO2 and H+ ALVEOLAR SPACE IN LUNG • Most CO2 is transported to the lungs in the form of bicarbonate ions CO2 CO2 CO2 CO2 H2O Hemoglobin releases CO2 and H+ H2CO3 HCO3– HCO3– Figure 22.11B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings + H+ 22.12 Connection: The human fetus exchanges gases with the mother’s bloodstream • A human fetus depends on the placenta for gas exchange Placenta, containing maternal blood vessels and fetal capillaries Umbilical cord, containing fetal blood vessels Amniotic fluid Uterus Figure 22.12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • A network of capillaries exchanges O2 and CO2 with maternal blood that carries gases to and from the mother’s lungs • At birth, increasing CO2 in the fetal blood stimulates the fetus’s breathing control centers to initiate breathing Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings