Like air-breathing fishes, amphibians use a
pulse pump to ventilate their lungs. Airflow is bidirectional.
The two-stroke buccal pump method of ventilation
is primitive for amphibians and is found in most. It has
been reported in some lungfishes (e.g., African lungfish).
A few aquatic amphibians use the four-stroke buccal pump.
When an amphibian is in water, the hydrostatic pressure
against the sides of its partially submerged body presses on
the lung to produce a pressure that is higher than atmospheric
pressure. When the amphibian exhales air, this
hydrostatic pressure aids in venting the lungs. In addition
to the passive effects of water pressure, hypaxial muscles
(especially the transverses abdominis) contract to actively
aid exhalation. This helps clear the lungs and produces a
larger tidal volume during infrequent breathing. However,
active muscle contraction apparently does not contribute
to inhalation. During inhalation, the buccal cavity must
work against this water pressure to refill the lungs.
A strong, muscular buccal cavity addresses this problem of
taking breaths of air while the animal is immersed in water.
On the other hand, the buccal cavity on which this buccal
pump is centered is also involved in feeding. As we will see
later in the chapter, the dual roles of the buccal cavity in
feeding and ventilation can lead to conflicting demands
and compromises in design.
Like air-breathing fishes, amphibians use apulse pump to ventilate their lungs. Airflow is bidirectional.The two-stroke buccal pump method of ventilationis primitive for amphibians and is found in most. It hasbeen reported in some lungfishes (e.g., African lungfish).A few aquatic amphibians use the four-stroke buccal pump.When an amphibian is in water, the hydrostatic pressureagainst the sides of its partially submerged body presses onthe lung to produce a pressure that is higher than atmosphericpressure. When the amphibian exhales air, thishydrostatic pressure aids in venting the lungs. In additionto the passive effects of water pressure, hypaxial muscles(especially the transverses abdominis) contract to activelyaid exhalation. This helps clear the lungs and produces alarger tidal volume during infrequent breathing. However,active muscle contraction apparently does not contributeto inhalation. During inhalation, the buccal cavity mustwork against this water pressure to refill the lungs.A strong, muscular buccal cavity addresses this problem oftaking breaths of air while the animal is immersed in water.On the other hand, the buccal cavity on which this buccalpump is centered is also involved in feeding. As we will seelater in the chapter, the dual roles of the buccal cavity infeeding and ventilation can lead to conflicting demandsand compromises in design.
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