Aspects of Vertebrate RespirationCountercurrent exchange in fish gills the most efficient respiratory systemFour gill arches on each side of head - each with two rows of gill filaments - divided into thin lamellae that project into flow of waterMovement of water across lamellae occurs in only one directionDirection of blood circulation runs opposite that of water flowCountercurrent flow maximizes difference in oxygen concentration between water and bloodCountercurrent exchange results in blood always being exposed to water with a higher oxygen concentration a diffusion gradient is maintained across surface of gillallows blood to become up to 85% saturated with oxygenA concurrent exchange system would allow nogreater than 50% saturationHow Hemoglobin WorksOxygen concentration of blood depends on oxygen concentration ofthe air or water from which it comesBlood plasma can contain only 3 ml O2/literWhole blood contains nearly 200 ml O2/literMost oxygen bound to hemoglobin inside red blood cellsHemoglobin - an O2 carrier protein - found in most animalsHas 4 polypeptidesubunitsEach subunit hasan iron containing heme groupO2 can be carriedby each subunitHemoglobin picks up O2 in lungs - becomes oxyhemoglobinbright red colorHemoglobin releases O2 at tissues - becomes deoxyhemoglobindark red color - looks blue under skinHb has asymptotic loading curve- completely deoxygenated Hb will take up the first and secondO2 molecules easily but picksup the third and fourth less easily- completely oxygenated Hb dumpsthe fourth and third O2 moleculereservedly but dumps the second and first more readily- allows low amounts of O2 to bedelivered to resting tissue andlarge amounts to active tissueHb is sensitive to pH and temperaturelow pH or high temperature results in a change in the loading curve - the curve shifts to the rightallows greater O2 delivery to tissue that have low pH or high temperatureLow pH in tissues is associated with active metabolism - throughproduction of CO2 and lactic acidH2O + CO2 H2CO3 H+ +
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