Directionality Of Air Flow In The Lungs Of Non-Avian Sauropsids

Emma HerdenerDr. John RubenDr. 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 uni-directional air flow or bi-directional 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 non-vascularized air sacs enable uni-directional air flow across lungs

• It is currently undetermined if non-avian sauropsids (reptiles) have uni-directional air flow or bi-directional air flow

Background: Uni-directional Air Flow vs. Bi-directional Air Flow

• Bi-directional: air moves in a bellowslike fashion, expanding vascularized lung during inhalation and contracting during exhalation

The smallest units of the mammalian lung are the saclike alveoli, which utilize bi-directional air flow. [Schmidt-Nielsen 1972]

Background: Uni-directional Air Flow vs. Bi-directional Air Flow

• Uni-directional: non-vascularized 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. [Schmidt-Nielsen 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 flow-through 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