[A] Structures + Respiration

• Factors that Affect Passive Diffusion

  1. Surface Area
  2. Distance between cells and gases diffusing
  3. Resistance of barrier
  4. Differences in partial pressure across exchange surface
• For diffusion to be effective, surface areas must be:

  1. Moist
  2. Thin
  3. Large
• Categories of Respiration:

  1. External
  2. Internal
  3. Ventilation
• External Respiration

  • Between blood & environment via respiratory surface
  • ex: gills, alveoli in lungs
  • Interaction is between blood & environment
• Internal Respiration

  • Occurs between blood and systemic tissues
  • Gas exchange between blood and internal tissues
• Two types of ventilation

  1. Unidirectional ventilation
  2. Bidirectional ventilation
• Movement of respiratory medium (water or air) across the exchange surface

  Ventilation
• Pumping blood through and organ via capillaries

  Perfusion
• Unidirectional Ventilation

  • Movement of respiratory medium only occurs in one direction
  • Buccal cavity → Gill curtain
  • Can lead to hypoxia or fish kill
• Bidirectional ventilation

  • More common in air breathing amniotes
  • A fresh breath of air that is inhaled into the lungs mixes with spent air and is exhaled
  • Capillaries as areas of gas exchange