A and P II - Anatomy Exam III essays Short Essays Factors...

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Anatomy Exam III essays Short Essays Factors that effect the rate of pulmonary and systemic gas exchange Partial Pressure difference of the gases- alveolar PO2 must be higher than blood PO2 for oxygen to diffuse from alveolar air into the blood. The rate of diffusion is faster when the difference between PO2 in alveolar air and pulmonary capillary blood is larger, diffusion is slower when the difference is smaller. The differences between PO2 and PCO2 in alveolar air versus pulmonary blood increase during exercise. The larger partial pressure differences accelerate the rates of gas diffusion. The partial pressure of O2 and CO2 in alveolar air also depend on the rate of airflow in and out of the lungs. Certain drugs [morphine] slow ventilation, thereby decreasing the amount of O2 and CO2 that can be exchanged between alveolar air and blood. With increasing altitude, the total atmospheric pressure decreases, as does the partial pressure of O2—from 159 mmHg at sea level, to 110 mmHg at 10,000 ft, to 73 mmHg at 20,000 ft. Although O2 still is 20.9% of the total, the PO2 of inhaled air decreases with increasing altitude. Alveolar PO2 decreases correspondingly, and O2 diffuses into the blood more slowly. Surface area available for gas exchange- the surface area of alveoli is huge. Many capillaries surround each alveolus, so that as much as 900mL of blood is able to participate in gas exchange at any instant. Any pulmonary disorder that decreases the functional surface area of the respiratory membranes decreases the rate of external respiration. For example, in emphysema alveolar walls disintegrate, so surface area is smaller than normal and pulmonary gas exchange is slowed Diffusion distance- the respiratory membrane is very thin, so diffusion occurs quickly. Also, the capillaries are so narrow that red blood cells must pass through them in single file, which minimizes the diffusion distance from an alveolar air space to hemoglobin inside red blood cells. Buildup of interstitial fluid between alveoli, as occurs in pulmonary edema, slows the rate of gas exchange because it increases diffusion distance. Molecular weight and solubility of gas- Because O2 has a lower molecular weight than CO2, it could be expected to diffuse across the respiratory membrance about 1.2 times faster. However, the solubility of CO2 in the fluid portions of the respiratory membrane is about 24 times greater than that of O2; taking bother of these factors into account, net outward CO2 diffusion occurs 20 times faster than net inward diffusion. Consequently, when diffusion is slower than normal, or example in emphysema or pulmonary edema, O2 insufficiency [hypoxia] typically occurs before there is significant retention of CO2 [hypercapnia]. Factors that effect percent saturation of hemoglobin
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This note was uploaded on 04/18/2008 for the course BIO 3040 taught by Professor Carr during the Spring '08 term at Palm Beach Atlantic University.

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A and P II - Anatomy Exam III essays Short Essays Factors...

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