# BIO-0014 Lecture Notes - Lecture 20: Circulatory System, Vascular Resistance, Partial Pressure

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25 Apr 2017
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1. Respiration
a. Gases in the atmosphere:
i. Nitrogen = 78%
ii. Oxygen = 21%
iii. Carbon Dioxide = 0.03%
iv. Partial Pressure Definition and Units
1. At sea level atmospheric pressure = 760 mm(millimeter)
Hg(mercury)
a. Therefore partial pressure of oxygen would be 21% times
760 mm Hg =160 mm Hg
2. Nitrogen partial pressure = 760 X 78% = 593 mm Hg
3. Carbon Dioxide partial pressure = 760 = 0.03% = 0.23 mm Hg
b. Kilopascal units (N/M2)
i. At sea level there is 101.3 kPa (sometimes rounded off to 100 kPa) of
pressure of 1 bar or 1000 millibars ( used in meteorology).
ii. Therefore oxygen is 21 kPa or 0.21 bars
iii. Nitrogen = 78 kPa or 0.78 bars
iv. Carbon dioxide = 0.03 kPa or 0.0003 kPa
1. Percentage of oxygen/carbon dioxide/ nitrogen stays the same as
you go higher( to like Mt. Everest). The total amount decreases
due to less atmosphere
v. The total pressure is equal to one atmosphere
c. Air versus Water
i. Air has 209 mL oxygen/liter
ii. Water has 6.6 mL oxygen/liter
iii. Water is 1000 times more dense than air
d. Henry’s Law (calculating how much gas can dissolve in a solution)
i. C = k x P
ii. C = concentration of dissolved gas (mmoles /liter or mg/L)
iii. P = partial pressure of gas (mm Hg)
iv. K = solubility constant of gas in solvent (mmoles/liter mm Hg or mg/L mm
Hg)
e. Diffusion versus Bulk Flow
i. Diffusion
1. relies on thermal energy; efficient over short distances
2. Requires no ATP
3. Only needs a partial pressure gradient
4. For example:
a.
5. J (rate of diffusion in mL or cm3 of gas/sec) = K x A(p2-p1)/D
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