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Chapter 42 Circulation and Gas Exchange Concept 42.5: Gas exchange occurs across specialized respiratory surfaces • Gas exchange supplies oxygen for cellular respiration and disposes of carbon dioxide • Animals require large, moist respiratory surfaces for adequate diffusion of gases between their cells and the respiratory medium, either air or water LE 42-19 Respiratory medium (air or water) O2 CO2 Respiratory surface Organismal level Circulatory system Cellular level Energy-rich fuel molecules from food Cellular respiration ATP LE 42-14 Tissue cell Capillary Red blood cell Net fluid movement out Net fluid movement in 15 µm Direction of blood flow Blood pressure Osmotic pressure Inward flow Pressure Capillary INTERSTITIAL or EXTRACELLULAR FLUID Outward flow Arterial end of capillary Venous end Surface-to-Volume Ratio • The rate at which an organism can absorb O2 or give off CO2 depends on its surface area – Need determined by volume Surface-to-Volume Ratio • The bigger the organism gets, its need for oxygen grows faster than its ability to supply that need. – SOLUTION: CREATE MORE SURFACE AREA! Proportional to SURFACE • Rate of gas exchange Proportional to VOLUME • O2 use; CO2 produced – Big = more O2 use • Rate of heat exchange (or heat loss) • Strength of limb • Heat production – Big = more heat production • Weight of an organism – More muscle, greater strength • Friction on an organism Different adaptations accommodate different needs Surface-to-Volume Ratio • Homeothermic Animals – Maintain body temp slightly higher than environment – Constantly lose heat – Heat produced depends on volume • Smaller = greater S/V ratio – More surface area to lose heat – So… smaller organism means it loses more heat – Must make it up by metabolizing more eat more • Consider this graph… metabolic rate metabolic rate Volume O2 needed Body mass unit time Heat loss elephant mouse Surface to volume ratio Respiratory Surfaces Body Surface • Gastrovascular cavities • Used by very small, cold-blooded animals – Planaria, protozoa, sponges, cnidaria Gills in Aquatic Animals • Gills are outfoldings of the body surface specialized for gas exchange • In some invertebrates, gills have a simple shape and are distributed over much of the body Gills Coelom Tube foot • Many segmented worms have flaplike gills that extend from each segment of their body Parapodia Gill The gills of clams, crayfish, and many other animals are restricted to a local body region Gills LE 42-20d Gills Crayfish • Problem: water is too dense and can take a lot of energy to move • Solution: Effectiveness of gas exchange in some gills, including those of fishes, is increased by ventilation and the countercurrent flow of blood and water – LE 42-21 Oxygen-poor blood Gill arch Gill arch Water flow Lamella Oxygen-rich blood Blood vessel Operculum Water flow over lamellae showing % O2 Gill filaments O2 Blood flow through capillaries in lamellae showing % O2 Countercurrent exchange Oxygen-poor blood Lamella Oxygen-rich blood Water flow over lamellae showing % O2 Countercurrent exchange O2 Blood flow through capillaries in lamellae showing % O2 Tracheal Systems in Insects • The tracheal system of insects consists of tiny branching tubes that penetrate the body Tracheae Air sacs Spiracle LE 42-22b Body cell Air sac Tracheole Trachea Air Tracheoles Body wall Mitochondria Myofibrils 2.5 µm Lungs • Spiders, land snails, and most terrestrial vertebrates have internal lungs Mammalian Respiratory Systems: A Closer Look • A system of branching ducts conveys air to the lungs • Pathway of air – Air inhaled through the nostrils passes through the pharynx into the trachea, bronchi, bronchioles, and deadend alveoli, where gas exchange occurs Branch from pulmonary vein (oxygen-rich blood) Branch from Pulmonary artery (oxygen-poor blood) Terminal bronchiole Nasal cavity Pharynx Larynx Trachea Right lung Bronchus Alveoli Left lung Bronchiole SEM Colorized SEM Epiglottis Esophagus Pleural membranes (pleurae) Diaphragm Concept 42.6: Breathing ventilates the lungs • The process that ventilates the lungs is breathing, the alternate inhalation (inspiration) and exhalation (expiration) of air How an Amphibian Breathes • An amphibian such as a frog ventilates its lungs by positive pressure breathing, which forces air down the trachea How a Mammal Breathes • Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs • Lung volume increases as the rib muscles and diaphragm contract 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)
