One of the most important factors affecting the diffusion of gases into and out

Question

One of the most important factors affecting the diffusion of gases into and out of the bloodstream is the concept of partial pressure. Partial pressure is the pressure exerted by a specific gas as part of a mixture of gases (in other words, the part of the overall pressure due to that specific gas). For example, 21% of Earth's atmosphere is oxygen (O2). At sea level, which has an atmospheric pressure of 760 mm Hg, the P_O2 is 21% of 760, or 0.21 x 760, which gives us 160 mm Hg.

For another example, consider the following: So-called oxygen bars are a fad that has waxed and waned over the last couple of decades. Oxygen bars provide patrons with nasal tubes of scented, concentrated O_2, claiming that inhaling the extra oxygen provided health benefits. O_2 concentrations can vary, but the average is about 40%. Assuming that the air pressure is the same as at sea level, what is the P_O2 in these breathing tubes? ---------- mm Hg

Question #2: Which of the following methods describe ways one could change the P_O2 in this environment? Check all that apply.

a. Increase or decrease the concentration of other gases in this atmosphere

b. Increase or decrease the concentration of oxygen in this atmosphere

c. Increase or decrease the air pressure in this atmosphere

Recall that molecules tend to diffuse down their concentration gradients, from areas of high concentration to areas of low concentration. In the case of gas exchange in the body, dissolved gases move from areas of high partial pressure to areas of low partial pressure.

The adjacent image illustrates a capillary blood vessel passing by bodily tissues. The blood is flowing from the top of the image to the bottom. Complete the diagram by identifying the relative partial pressure of CO_2 in the blood and in the tissue cells when the blood first enters the capillary, which direction the CO-2 diffuses, and what the relative partial pressure in the blood and in the tissue cells are when the blood exits the capillary.

P_CO2 relatively (equal, high, or low) top left

P_CO2 relatively (equal, high, or low) bottom left

CO_2 diffuses (equal, high, or low)

P_CO_2 relatively (equal, high, or low) top right

P_CO_2 relatively (equal, high, or low) bottom right

Question #3

Many different variables contribute to the overall efficiency of gas exchange across a respiratory membrane. The following table lists four of these factors. For each, identify whether the listed change will result in an increase or decrease in the rate of gas transfer.

Respiratory Factor Influence on Gas Exchange Increase in diffusion constant Increase in rate of gas transfer or decrease in rate of gas transfer Decrease in thickness of respiratory membrane Increase in rate of gas transfer or decrease in rate of gas transfer Decrease in surface area Increase in rate of gas transfer or decrease in rate of gas transfer Increase in partial pressure gradient Increase in rate of gas transfer or decrease in rate of gas transfer en le of sthe

Explanation / Answer

1) 40% x 760mm of Hg

= 0.40x 760mm of Hg

=304mm of Hg

2)partial pressure of oxygen in atmospheric air= 159

Partial pressure of carbon dioxide in atmospheric air= 0.3

Partial pressure of oxygen and carbon dioxide in alveoli are 104 and 40 respectively

Partial pressure of oxygen and carbon dioxide in deoxygenated blood are 40 and 45 respectively.

Partial pressure of oxygen and carbon dioxide in oxygenated blood are 95 and 40 respectively.

Partial pressure of oxygen and carbon dioxide in tissues are 40 and 45 respectively.

Note- above mentioned values are in mm of Hg

3) (a) diffusivity or diffusion constant is a proportionality constant between molar flux due to molecular diffusion and the gradient in concentration of species. The higher the diffusivity of one substance with respect to another, the faster they diffuse into each other.

(b)thickness of respiratory membrane is inversely proportional to gas exchange so decrease in thickness of respiratory membrane increases the rate of gas transfer.

(c)surface area is directly proportional to gas exchange so decrease in surface area will decrease the rate of gas transfer.

(d)partial pressure gradient is directly proportional to gas transfer so increase in partial pressure gradient increase the rate of gas transfer.

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