[B] Muscular Ventilatory Mechanisms

• 2 types of muscular ventilatory mechanisms

  • Water ventilation - Dual pump
  • Air ventilation - Buccal pump and aspiration pump
• Water ventilation occurs in a dual pump system:

  • Buccal pump - mouth
  • Opercular pump - associated with gill operculum
• Water ventilation involves synchronous pumping of both pumps

  • Pumps water across a single direction
  • Results in unidirectional flow across gills
• 2 phases of two stroke water pumping

  • Suction phase
  • Opening of buccal and oral cavity creates lower pressure
  • Rush into mouth where pressure is lower
  • Force phase
  • Closing of oral valve
  • Causes change of pressure
  • Water flow into opercular cavity and exit in opercular valve
• Air ventilation loses the opercular pump, and relies on the buccal cavity
• 4-stroke pumping system:

  1. First stage expansion
  2. Expansion of buccal cavity
  3. Draws out expired air from lungs
  4. Second stage compression
  5. Compression of buccal cavity
  6. Forces gas out through nares
  7. Third stage expansion
  8. Fresh air into buccal cavity
  9. Brings in gas via nares
  10. Fourth stage compression
  11. Buccal compression, fresh air into lungs
• 2-stroke pumping system:

  1. Expansion of buccal cavity
  2. Fresh air drawn in
  3. Expired air drawn out from lungs
  4. Compression of buccal cavity
  5. Most of expired air exit into environment
  6. Mix of fresh and expired air drawn into lungs
• Aspiration pump:

  1. Does NOT push against resisting force
  2. Diaphragm acts as aspirator
  3. Lower volume of lungs
  4. Air rushes in to fill lower pressure lungs
  5. Pump of rib cage and diaphragm
  6. Tidal movement of air
  7. Amniotes have this type of ventilatory mechanism
  8. Evolutionary consequence of respiratory and digestive decoupling
  9. Buccal pump not involved