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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