Ventilation mechanism

• During ventilation air sacs inside insect act as bellows and muscles inside contract and relax
• muscles Attached to the floor and roof of abdominal cavity contract pulling it together
• Decreases the volume , increasing the pressure and forcing air out - expiration is active
• When muscles relax - the increased volume decreases the pressure and air flows in - inspiration is passive
• Air diffuses I’m down a diffusion gradient - maintained as oxygen is used up by respiring cells
• For air to come in or out , valves on spiracles open (normally closed to prevent water loss)
• At rest air is drawn in through the thoracic spiracles - these then close and is expelled through a few abdominal spiracles

  during activity - expiration involves more abdominal spiracles
• When the spiracles are open , oxygen diffuses in along its gradient
• Carbon dioxide can leave through spiracles bus also diffuse into the blood to be removed through the cuticle
• Flow through tracheae is unidirectional from thorax towards abdomen
• Flow through the tracheoles is tidal
• Insects in dry environments have a fluttering mechanism to partially open spiracles - decreases total time spiracles are open and therefore conserves water loss
• Spiracles only open completely if carbon dioxide concentration increases too far or oxygen concentration decreases too far
• Insects have further adaptations to prevent water loss caused by gases exchange - have waxy cuticle and tiny hairs around spiracles which reduce evaporation