A. Partial Pressure Gradients
1. Respiratory systems rely on the diffusion of gases down pressure gradients.
a. Air is 78% nitrogen, 21% oxygen, 0.04% carbon dioxide, and 0.96% other gases.
b. Partial pressures for each gas in the atmosphere can be calculated; for example, oxygen’s is 160mm Hg.
c. Oxygen and carbon dioxide diffuse down pressure gradients from areas of high partial pressure to areas of low partial pressure.
2. Diffusion will occur across a respiratory surface if it is thin, moist.
3. The speed and extent of diffusion depends on the surface area present in the respiratory organs.
B. Transport Pigments
1. Hemoglobin is the main transport pigment.
2. Each molecule binds four molecules of oxygen in the lungs (high concentration) and releases them in the tissues where oxygen is low.