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3/18/15 Chapter 21: Principles of gas exchange Principles of gas exchange 1.  Respiratory gases and movement through the body –  Diffusion –  Bulk flow (convecIon) –  CombinaIon 2.  Principles of transport –  Oxygen cascade –  Physical properIes of air and water Respiratory gases 3 mechanisms of gas exchange •  What are the main gases in respiraIon? –  CO2 and O2 1.  Diffusion: Movement from high à low concentraIon 2.  Bulk flow (convecIon): Gas molecules carried in a soluIon (gas or liquid) 3.  CombinaIon of both •  CONSTANT gas exchange across membranes –  All physiological processes require energy • 
RespiraIon, metabolism, neural impulses, muscles, .... –  CO2 accumulaIon acidifies internal environment Diffusion Diffusion Movement from high à low concentraIon HIGH EQUILIBRIUM Movement from high à low concentraIon Movement from low à high concentraIon?? 1.  Liquid and gas soluIons have different parIal pressures Movement: High pressure à low pressure LOW 1 3/18/15 Diffusion during diving •  Pressure of N2 in water increases with depth –  As pressure increases in water, N diffuses INTO lungs FROM water unIl at equilibrium with water –  Ascending => N2 diffuses out of blood into bubbles Diffusion during diving •  Pressure of N2 in water > lungs –  At depth => N2 in lungs at equilibrium with water –  Ascending => N2 diffuses out of blood into bubbles • 
Ascend too fast, diffusion can’t keep up! 33 meters Surface Diffusion •  Gases diffuse faster in gas than liquid –  Slow diffusion in body Issues •  Developing Sea Turtle embryos buried in sand need O2 •  Dry, porous soil à fast diffusion •  Wet, saturated soil à slow diffusion à embryos die Transport via Bulk flow 1.  UnidirecIonal –  Blood flow through blood vessels 2.  Tidal (bidirecIonal): back and forth –  Air flow through lungs 3 mechanisms of gas exchange 1.  Diffusion 2.  Bulk flow (convec8on): –  Gas molecules carried in a solu8on (gas or liquid) •  Transport is faster than diffusion BUT requires Energy to transport Circulatory system carries O2 in blood Transport via Bulk flow •  Want bulk flow to be FAST •  Faster bulk flow by: 1.  Greater concentraIon of gas in medium being transported “send more stuff” 2.  Faster flow rate “get it there faster” 2 3/18/15 Diffusion and Bulk flow •  Transport via bulk flow: –  Diffusion only useful –  PRO: faster than diffusion –  CON: requires energy for short distances –  Organisms use a combinaIon Principles of gas exchange 1.  Respiratory gases and movement through the body –  Diffusion –  Bulk flow (convecIon) –  CombinaIon 2.  Principles of transport –  Oxygen cascade –  Physical properIes of air and water Oxygen Cascade Physical properIes of air and water •  As O2 transported over membrane, p pressure ê –  Diffusion rate across these areas? –  Where does diffusion occur? Bulk flow? –  Mitochondria are ulImate desInaIon. WHY? AIR WATER Density -­‐ ++ Viscosity -­‐ ++ •  Greater density and viscosity à gases (in water) are harder to move through body •  Water breathing animals expend more E to move O2 Physical properIes of air and water AIR WATER Density -­‐ ++ Viscosity -­‐ ++ O2 concentraIon ++ -­‐ •  Air contains more O2 per unit volume •  Air breathing is easier and more efficient => EVOLUTIONARY ADVANCEMENT 3