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Directionality Of Air Flow In T he Lungs Of Non-Avian Sauropsids

Directionality Of Air Flow In T he 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

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Directionality Of Air Flow In T he Lungs Of Non-Avian Sauropsids

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  1. Directionality Of Air Flow In The Lungs Of Non-Avian Sauropsids Emma Herdener Dr. John Ruben Dr. Devon Quick

  2. 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

  3. 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

  4. 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 extensivenonvascularized regions of the lungs as well as by relativelypoor vascularization of the septae

  5. 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

  6. 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]

  7. 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]

  8. 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)

  9. 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

  10. 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

  11. 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

  12. Methods • Comparisons of lung morphology between crocodilians and reptiles made to ensure procedures would be possible

  13. Methods: Differences Between Crocodilian and Reptile Lung • Reptile lung possesses larger non-vascularized air sac

  14. 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

  15. Equipment • CT scans utilized to ensure correct placement in the lungs

  16. Methods • Plan to complete testing in live animal (study species Varanus) to determine directionality of air flow

  17. 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

  18. Acknowledgments • HHMI program & Dr. Kevin Ahern • OSU Honors College • Dr. John Ruben and Dr. Devon Quick

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