Directionality Of Air Flow In The
Lungs Of Non-Avian Sauropsids
Emma Herdener
Dr. John Ruben
Dr. Devon Quick
Overview of Experiment
• Observe qualities of extant
organisms to better
understanding of:
– Evolution of lungs/breathing
– Mechanisms of respiration for
extinct organisms
• Determine whether reptilian
septate lungs maintain unidirectional air flow or bidirectional air flow
Background: Differences Between
Septate Lungs And Alveolar Lungs
• Septate lungs thought to be ancestral; alveolar lungs
derived
• Septate lungs analogous to a single alveolus in an
alveolar lung
• Gas exchange occurs along vascularized ingrowths
throughout lungs called septae
• Sites of gas exchange surfaces in (A) alveolar
(mammalian) and (B) modified septate (avian) lungs.
• Whole-lung cross (C) of unmodified sauropsid septate
lungs. Reptilian lungs have limited O2-CO2 exchange
due to the absence of extensive nonvascularized
regions of the lungs as well as by relatively poor
vascularization of the septae
Background: Differences Between
Septate Lungs And Alveolar Lungs
• In birds, large, highly
extensive nonvascularized air sacs
enable unidirectional air flow
across lungs
• It is currently
undetermined if nonavian sauropsids
(reptiles) have unidirectional air flow
or bi-directional air
flow
Background: Uni-directional Air Flow
vs. Bi-directional Air Flow
The smallest units of the
mammalian lung are the
saclike alveoli, which utilize
bi-directional air flow.
[Schmidt-Nielsen 1972]
• Bi-directional: air moves in a bellowslike
fashion, expanding vascularized lung during
inhalation and contracting during exhalation
Background: Uni-directional Air Flow
vs. Bi-directional Air Flow
• Uni-directional: nonvascularized portions of lungs
hold air at different points in
the respiratory cycle. This
enables air to move across
the vascularized portions of
the lungs in a fixed direction
both during inhalation and
exhalation. Air always flows
from posterior to anterior,
and the vascularized portions
of the lungs maintain a fixed
volume.
The smallest units of the bird lung are
tubes that are open at both ends and
permit air through them. [SchmidtNielsen 1972]
Relation Of Diaphragm To Breathing
• Presence of diaphragm only
occurs in mammals and
crocodilians – negative
pressure (contraction of the
diaphragm) enables
expansion of lung (A & B)
• Modern birds and reptiles
utilize costal breathing
(expansion/contraction of
ribcage). Birds also rely
heavily on a unique flowthrough system made
possible by the elevation
and depression of the
sternum (C)
Hypothesis
• Due to shared characteristics between both
crocodilian traits (absence of extensive
nonvascularized regions of the lungs) and
avian traits (ability to maintain uni-directional
air flow through lungs with the absence of
diaphragm), it is probable that other reptiles
(e.g. lizards) also maintain uni-directional air
flow
Methods
• Testing For Air Pressure:
– Pressure probes will be used to determine
pressure in different parts of the lungs to
determine directionality
• Obtaining operational pressure probes was a
novel and significant part of this experiment
Equipment
• Probes are tested in a
dead animal to ensure
correct methods and best
procedures for minimum
invasion and stress
• Similarities between
reptilian and crocodilian
lungs and availability of
dead crocodilians made
crocodilians the logical
choice
Methods
• Comparisons of lung
morphology between
crocodilians and
reptiles made to
ensure procedures
would be possible
Methods: Differences Between
Crocodilian and Reptile Lung
• Reptile lung
possesses larger
non-vascularized air
sac
Methods: Differences Between
Crocodilian and Reptile Lung
• Crocodilian lung possesses
larger openings within
vascularized portion of
the lung
• Reptilian lung, although
more cartilaginous,
possesses smaller
openings in lung that
restrict placement of
probes
Equipment
• CT scans utilized to ensure correct placement
in the lungs
Methods
• Plan to complete testing in live animal (study
species Varanus) to determine directionality
of air flow
Goals
• Data from these experiments enhances
understanding of basic lung ventilatory
patterns in extant reptiles and might provide
insight into similar and related physiological
processes in a number of extinct organisms
Acknowledgments
• HHMI program & Dr. Kevin Ahern
• OSU Honors College
• Dr. John Ruben and Dr. Devon Quick