Gas Exchange
Graphics are used with permission of:
Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com)
Page 1. Introduction
• Oxygen and carbon dioxide diffuse between the alveoli and pulmonary capillaries in the lungs, and
between the systemic capillaries and cells throughout the body.
• The diffusion of these gases, moving in opposite directions, is called gas exchange.
Page 2. Goals
• To apply gas law relationships - between partial pressure, solubility, and concentration - to gas
exchange.
• To explore the factors which affect external and internal respiration.
Page 3. Dalton's Law of Partial Pressures
• Fill out this chart as you work through this page:
• In order to understand gas exchange, we must first understand the air we breathe. The atmosphere
is a mixture of gases, including oxygen, carbon dioxide, nitrogen, and water.
• The combined pressure of these gases equals atmospheric pressure.
• At sea level, atmospheric pressure is 760 mm Hg, which means that the atmosphere pushes a
column of mercury to a height of 760 millimeters. Each gas within the atmosphere is responsible
for part of that pressure in proportion to its percentage in the atmosphere.
• Oxygen comprises 20.9% of the atmosphere. The pressure exerted by oxygen is 20.9% of the total
pressure of 760 millimeters of mercury, which equals 159 millimeters of mercury. This value is
known as the partial pressure of oxygen, and is written as "P" with the subscript "O2".
• Notice that the partial pressures of the four gases add up to 760 millimeters of mercury, the total
atmospheric pressure. This demonstrates Dalton's Law of Partial Pressures, which states that in a
mixture of gases, the total pressure equals the sum of the partial pressures exerted by each gas.
The partial pressure of each gas is directly proportional to its percentage in the total gas mixture.
