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# A&P chap 3

### Jardins Diffusion of Pulmonary Gases

QuestionAnswer
Mechanics of ventilation moves bulk amounts of air in and out of lungs.
Diffusion gradients Individual gas partial pressure differences
Dalton's Law Total pressure exerted by mixture of gases is equal to sum of pressures exerted independently by each gas in mixture.
Earth's atmospheric gases Nitrogen N2, oxygen O2, carbon dioxide CO2, and others
Determining partial pressure of each gas. multiplying PB by percentage of gas in atmosphere.
Percentage and partial pressure of Nitrogen PN2 592.8mm Hg, 78.08%
Percentage and partial pressure of Oxygen PO2 159.6mm Hg, 20.95%
Percentage and partial pressure of Carbon dioxide PCO2 0.2mm Hg, 0.03%
Percentage and partial pressure of other gases. 7mm Hg, 0.93%
What does atmospheric pressure do when altitude increases. decreases
What does partial pressure exerted by each gas do when density of atmospheric gases decrease. Decreases, e.g. PO2
Atmospheric pressure increases by 1 atmosphere (760mm Hg) for each 33 ft of descent (in water) below sea level. Partial pressure exerted by each gas in atmosphere is increased four times.
Pressure gradient movement of gas from high to low pressure areas. Primary mechanism responsible for moving air in and out of lungs during ventilation. Each individual gas moves in same direction, either in or out of lungs.
Gas diffusion movement of individual gas molecules from high to low pressure areas. Each individual gas can continue to move independently. Directly proportional to the difference in partial pressure of the gas between the two sides.
Kinetic energy driving force responsible for diffusion. "things bouncing against each other"
Two different gases can move (diffuse)in opposite directions based on individual diffusion gradients. normal circumstances O2 diffuses from alveoli into pulmonary capillaries while CO2 diffuses from pulmonary capillaries into alveoli.
Why is PO2 in the atmosphere so much higher than the PO2 in the alveoli other gases come into play, venous admixture.
Water Vapor pressure water can exist as liquid, gas or solid. Water vapor or molecular water - water in gaseous. Alveolar gas is assumed to have absolute humidity of 44mg/L and water vapor pressure of 47torr.
Ideal alveolar gas equation PAO2=[PB-PH2O]FIO2-PaCO2
Clinical ideal alveolar gas equation when PaCO2 is less than 60 drop off the 1.25
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. Solubility and temp are inversely related. CO2 is more soluble than O2, dissolves quicker and better in blood.
Graham's Law The rate (speed) of diffusion of gas through a liquid is directly proportional to solubility of gas. Inversely proportional to square root of gram-molecular weight (GMW) of gas.
Combining Grahams and Henrys law, rates of diffusion of 2 gases are directly proportional to ratio of their solubility. inversely proportional to ratio of their GMWs.
When Grahams and Henrys law are used to determine the relative rates of diffusion of O2 and CO2 CO2 diffuses about 20 times faster than O2.
Area (A) component of Ficks law verified when Decreased alveolar surface area. Alveolar collapse or fluid which decreases ability of O2 to enter pulmonary capillary blood.
P1-P2 portion of Fick's law confirmed when Decreased alveolar oxygen pressure (PAO2 or P1). Caused by high altitude or alveolar hypoventilation, which reduces diffusion of O2 into pulmonary capillary blood.
Thickness (T) factor is confirmed when increased alveolar tissue thickness reduces the movement of O2 across alveolar capillary membranes. Caused by alveolar fibrosis or alveolar edema.
Perfusion limited Transfer of gas across alveolar wall is a function of the amount of blood that flows past alveoli. Amount=volume, speed=blood flow.
Diffusion of Nitrous oxide. N2O quickly equilibriates with pulmonary blood. When equilibrium occurs, diffusion of N2O stops
Diffusion Limited movement of gas across the alveolar wall is a function of the integrity of the alveolar capillary membrane itself. Factor of Fick's Law. "whats going on in the membrane"
Clinical conditions that cause diffusion problems. Decrease the rate of gas diffusion - diffusion limited problems. Atelectasis, Pneumonia, Emphysema, Intersitial Edema, Pulmonary Edema, Alveolar Fibrosis.
Diffusion of O2 is perfusion limited under normal resting conditions diffusion of o2 perfusion limited. diffusion - diseased, perfusion - rest and healthy.
The normal transit time for blood through the alveolar capillary system is about .75 seconds
Under normal resting conditions, the diffusion of oxygen and carbon dioxide is usually completed in about 0.25 seconds, one-third of the time available.
Created by: hkirkendall75