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CP Phys Chap 3

Diffusion of Gases

QuestionAnswer
Respiration Exchange of gases at the capillary level, primarily O2 & CO2.
External Respiration Occurs in the pulmonary capillaries, between the Alveolar Air and Blood.
Internal Respiration Occurs in the systemis system, between the Blood & Tissues.
Diffusion The movement of gas molecules from an area of higher partial pressure to an area of lower partial pressure.. Gas moves according to their 'individual' partial pressures and continues until gas reaches equilibrium.
Boyle's Law P1V1=P2V2 - Temperature is constant & pressure varies inversly to volume.
Charle's Law V1/T1=V2/T2 - Pressure is constant & volume changes directly with temperature.
Gay-Lussac's Law P1/T1=V2/T2 - Volume is constant & temperature changes directly with pressure.
Combined Gas Law P1V1/T1=P2V2/T2 - No constant!
Dalton's Law of Partial Pressure In a mixture of gases, the total pressure is equal to the sum of the partial pressures of each separate gas.
Increased altitude = Decrease in barometric pressure, in gas density and the partial pressure of the gases. BUT fractional concentrations of gases do NOT change.
Water vapor pressure Must be subtracted from total pressure before calculations are made.
Ideal Alveolar Gas Equation PAO2 = (PB - Ph2o) Fio2 - Paco2 (1.25)
PAO2 = (PB - Ph2o) Fio2 - Paco2 (1.25) Partial pressure of O2 in the alveoli = (barometric pressure - partial pressure of H2O (47mmHg)) fractional concentration of inspired O2 - partial pressure of arterial CO2 (1.25)
Alveolar capillary membrane Composed of 8 layers. Its thickness is between 0.36 & 2.5 microns.
One micron = 1/25,000 of an inch
Oxygen Norms PvO2 = 40 TORR PAO2 = 100 TORR Pressure gradient = 60 TORR
Carbon Dioxide Norms PVCO2 = 46 TORR PACO2 = 40 TORR Pressure gradient = 6 TORR
O2 & CO2 Diffusion Diffuse until gas pressure in the alveoli and pulmonary capillaries are in equilibrium. Normally occurs in 0.25 sec & transit time for blood in pulmonary capillary system is 0.75 sec.
Diseased Lungs Gases may not reach equilibrium; due to pulmonary consolidation, fibrosis, edema or interstitial edema.
Flick's Law v (gas flow) = (P1-P2)AD/T - flow inversly related to thickness and directly related to the rest!
v (gas flow) = (P1-P2)AD/T gas flow = (pp 1 - pp 2)(area)(diffusion constant)/thickness
Henry's Law The amount of gas that dissolves in a liquid at a given temperature is proportional to the partial pressure of the gas.
> partial pressure = the more gas will dissolve
< pt temp = less gas will dissolve
Solubility Coefficient The amount of gas that can be dissolved in 1mL of a liquid at 760 TORR and a specified temperature. Each gas has its OWN!
At 37 degress & 760 TORR Solubility coefficient of: oxygen = 0.0244 mL/torr/H2O carbon dioxide = 0.592 mL/torr/H2O (24x faster that O2)
For every 10% > in O2 above room air = Your PAO2 should go up 50 TORR, i.e. 21% = 100 TORR 30% = 150 TORR 40% = 200 TORR 50% = 250 TORR
Created by: mfredenburg