Circulation and Gas Exchange

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Simon Fraser University
Biological Sciences
BISC 101
Tony Williams

Chapter 42 Circulation and Gas Exchange Gas exchange occurs by diffusion only works if y It occurs over short distances 12 cells y With large surface areas for exchange Large multicellular animals circulatory systems link gas exchange surfaces with cells throughout the body y Circulatory systems minimize the distance substances must diffuse to enterleave cell y O2 from inhaled air diffuses across only 2 cell layers in lungs y At tissues O2 again diffuses only short distance from blood in capillaries to cells Open Circulatory System anthropods most mollusks y Circulatory fluid hemolymph y Bathes organs directly interstitial fluid y Multiple tubular hearts y Low hydrostatic pressure low cost Closed Circulatory System annelids cephalopods all vertebrates y Circulatory fluid blood y Confined to vessels to separate from interstitial fluid y High BP increases effectiveness of O2 delivery in large active animals Vertebrate closed circulatory system cardiovascular system Single Circulation fish y Blood passes through heart once atriumventricle y Heart only sees oxygenpoor blood Double Circulation amphibians reptiles mammalsbirds y Double circuit pulmocutaneous circuit systemic circuit Pulmonary circuitsystemic circuit Amphibians o 3chambered heart o oxygenpoor blood skin and lungs o permits shutting off blood flow to temporarily ineffective lungs Reptiles o 3chambered heart o incomplete septum partially splits ventricle o rightsystemic artery oxygen poor blood mixes with oxygenated blood later o allows to shunt blood away from lungs temporarily when underwater Mammals o 4chambered heart o complete septum o oxygenpoor blood and oxygenrich blood are separated Coordinated cycles of heart contraction drive double circulation y but all components of the CVS function together to meet O2 demand o heart arteriesveins capillaries
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