Question
The partial pressure of oxygen in the lungs is about $150 \mathrm{mm}$ of Hg. (The partial pressure is the pressure of the oxygen alone, if all other gases were removed.) This corresponds to a concentration of $5.3 \times 10^{24}$ molecules per $\mathrm{m}^{3}$. In the oxygen-depleted blood entering the pulmonary capillaries, the concentration is $1.4 \times 10^{24}$ molecules per $\mathrm{m}^{3} .$ The blood is separated from air in the alveoli of the lungs by a $1-\mu \mathrm{m}$ -thick membrane. What is the rate of transfer of oxygen to the blood through the $5 \times 10^{-9} \mathrm{m}^{2}$ surface area of one alveolus? Give your answer in both molecules/s and $\mu \mathrm{mol} / \mathrm{s}$. Assume The diffusion coefficient for oxygen in tissue is $2 \times 10^{-11} \mathrm{m}^{2} / \mathrm{s}$. Give your answer to 1 significant figure.
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This can be calculated as follows: \[\Delta C = C_{\text{lungs}} - C_{\text{blood}} = 5.3 \times 10^{24} \, \text{molecules/m}^3 - 1.4 \times 10^{24} \, \text{molecules/m}^3 = 3.9 \times 10^{24} \, \text{molecules/m}^3\] Show more…
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II The small capillaries in the lungs are in close contact with the alveoli. A red blood cell takes up oxygen during the $0.5 \mathrm{s}$ that it squeezes through a capillary at the surface of an alveolus. What is the diffusion time for oxygen across the $1-\mu \mathrm{m}$ -thick membrane separating air from blood? Assume that the diffusion coefficient for oxygen in tissue is $2 \times 10^{-11} \mathrm{m}^{2} / \mathrm{s}$. Give your answer to 1 significant figure.
When air is inhaled, it enters the alveoli of the lungs, and varying amounts of the component gases exchange with dissolved gases in the blood. The resulting alveolar gas mixture is quite different from the atmospheric mixture. The following table presents selected data on the composition and partial pressure of four gases in the atmosphere and in the alveoli: If the total pressure of each gas mixture is 1.00 atm, calculate: (a) The partial pressure (in torr) of each gas in the atmosphere (b) The mole $\%$ of each gas in the alveoli (c) The number of $\mathrm{O}_{2}$ molecules in 0.50 $\mathrm{L}$ of alveolar air (volume of an average breath of a person at rest) at $37^{\circ} \mathrm{C}$
Calculating Lung Volume in Humans. In humans, oxygen and carbon dioxide are exchanged in the blood within many small sacs called alveoli in the lungs. Alveoli provide a large surface area for gas exchange. Recent careful measurements show that the total number of alveoli in a typical pair of lungs is about $480 \times 10^{6}$ and that the average volume of a single alveolus is $4.2 \times 10^{6} \mu \mathrm{m}^{3} .$ (The volume of a sphere is $V=\frac{4}{3} \pi r^{3},$ and the area of a sphere is $\left.A=4 \pi r^{2} .\right)$ If we assume that alveoli are spherical, what is the diameter of a typical alveolus? (a) $0.20 \mathrm{~mm} ;$ (b) $2 \mathrm{~mm} ;$ (c) $20 \mathrm{~mm} ;$ (d) $200 \mathrm{~mm}$.
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