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BIOL 273
Katherine Wood

Unit 5Respiratory System Chapter 18 Gas Exchange and TransportAir movement from alveoli to cells o Exchange of gases between two compartmentsdiffusion across cell membranes o Transport of gases in blood DIFFUSION AND SOLUBILITY OF GASESDiffusion between alveoli and pulmonary capillariesFicks law of diffusion o Diffusion ratesurface area x gradient x membrane permeabilitymembrane thicknessMembrane permeability is constantFour factors affect thisSurface areadirectly proportional o Usually constantgradientdirectly proportional o Most important factorMembrane thicknessinversely proportional o Usually constantDiffusion distancefaster over short distances o Usually constantRespiratory physiologygradientpartial pressure to express gas concentrations o Compare partial pressures of gases o Establishes gradient between alveoli and blood Dissolved Gas Depends on Pressure Solubility and TemperatureWater in contact with gaspressure gradient o Higher gas pressure in watergas molecules leave water o Higher gas pressure in gasgas dissolves into waterMovement of gas molecules from air to liquiddirectly proportional to o Pressure gradient of gasAt equilibriumex 100 mmHg of oxygen in both liquid and gasDoes not mean is the samedepends on solubility or oxygen in liquid o Solubility of gas in liquidhow easy the gas dissolves into liquidVery solublelarge number of gas molecules go into solution at low gas partial pressureLess solubleat high partial pressure only a few molecules go into solutionof oxygen dissolved in waterpartial pressure of gas dissolved in solution o TemperatureConstant in mammalsOxygen solubility vs carbon dioxide solubility o Carbon dioxide more soluble in water than oxygen o When pressure reaches equilibriumcarbon dioxide would have a higher concentration in liquid than oxygenmore soluble GAS EXCHANGE IN THE LUNGS AND TISSUESGas flows from higher partial pressure to lower partial pressureNormal alveolar partial pressure of oxygen100 mmHg o Partial pressure of oxygen arriving from venous circulation to lungs40 mmHg o Oxygen moves from alveoli to capillaries o Goes to equilibrium o Arterial blood leaving lungsalveoli partial pressure of oxygen100 mmHg o Arterial blood reaches capillaries Intracellular partial pressure of oxygen40 mmHgArterial blood partial pressure of oxygen100 mmHgOxygen moves from plasma into cellsDiffusion goes to equilibriumVenous blood has same partial pressure of oxygen as the cells it passedPartial pressure of carbon dioxide higher in tissue than systemic capillariesproduction during metabolism o Cellular partial pressure of carbon dioxide46 mmHgArterial40 mmHg
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