Physiology 2130 Lecture Notes - Lecture 49: Blood Gas Test, Gas Exchange, Partial Pressure
1 May 2018
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Lecture 049: Structure and Function of the Lung
Function of the Lung
Gas Exchange
● The exchange of O2 from the air (external environment) into the blood, and CO2 from the
blood (internal environment) into the air
● O2 dissolves into the blood at the capillary of the lungs and is pumped to the rest of the
body by the heart
● We say “arterial blood” we are usually talking about the systemic arteries
○ We get the blood gas values there
○ This is because this is an easier spot to get blood to measure
● Gas exchange within the lung occurs by diffusion
○ Diffusion occurs according to Fick’s Law of Diffusion
■ Vgas = Constant * (P1-P2) * A / T
Vgas
Volume of gas transferred per unit of time
Constant
Diffusion constant
● Is a property of the gas
● Directly proportional to the gas solubility
○ More soluble, larger constant
● Inversely proportional to the molecular weight of the molecule
○ Smaller molecule, larger constant
P1-P2
Difference in partial pressure (pressure gradient) in the two locations
● The larger the difference, the faster the diffusion
A
Area of tissue sheet
● The larger the area, the faster the gas can diffuse
T
Thickness of tissue sheet
● The thicker the sheet, the slower the gas can diffuse
● In the lung, there is:
○ A large area and thin interface
■ The blood-gas barrier in the capillaries are only 1 cell thick
○ Large pressure gradient
■ Due to the blood flow
○ Large constant
■ Property of the gas and the barrier
What is the Partial Pressure of a Gas? How does it apply to gas within a liquid?
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Document Summary
Lecture 049: structure and function of the lung. The exchange of o2 from the air (external environment) into the blood, and co2 from the blood (internal environment) into the air. O2 dissolves into the blood at the capillary of the lungs and is pumped to the rest of the body by the heart. We say arterial blood we are usually talking about the systemic arteries. We get the blood gas values there. This is because this is an easier spot to get blood to measure. Gas exchange within the lung occurs by diffusion. Diffusion occurs according to fick"s law of diffusion. Vgas = constant * (p1-p2) * a / t. Volume of gas transferred per unit of time. Inversely proportional to the molecular weight of the molecule. Difference in partial pressure (pressure gradient) in the two locations. The larger the difference, the faster the diffusion. The larger the area, the faster the gas can diffuse.
