Respiratory Anatomy/Physiology

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Respiratory Anatomy/Physiology

• P. T. Redig

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Functions of Respiratory System

• Supply Oxygen
• Remove carbon dioxide
• Thermoregulate
• Acid-base balance (respiratory component)
• Mechanism for vocalizations

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Amazing Facts about the Avian Respiratory System

• Tracheal rings are complete
• Some birds have two tracheas
• Trachea is 2.7x longer and 1.3x wider than
  trachea of a comparably-sized mammal
• Anatomic dead space is 4.5x larger than that of
  comparably-sized mammal
• Airflow is most of the lung is unidirectional (no
  alveoli)
• System can support sustained migratory flight at
  altitudes greater than 20,000f msl

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Additional Facts

• Lungs are rigid -- relatively little expansion
  and contraction
• Air is moved by airsacs which function as a
  bellows, of which there a 9
• Diverticula of the airsacs enter many long bones
• Both inspiration and expiration require muscle
  activity
• They have no diaphragm

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More Facts

• 50 - 80 of blood in the avian lung is in contact
  with gas exchange membranes compared to 20 in
  mammals
• The gas-blood barrier in avian lungs is
  significantly thinner than in mammalian lungs
• Avian lungs have CO2 receptors which play a role
  in regulation of respiration

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Anatomical Issues Upper Respiratory Tree

• Head/Beak/Sinuses
• Choanal Slit (cleft palate)
• Glottis/larynx
• Trachea
• Syrinx

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Beak with Operculum
Operculum
Nare
Structure labelled b is a turbinate bone
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Conch
The Conch (c) is the most proximal of the
turbinate bones and is confluent with the
infraorbital sinus. Also, a and b are other
turbinate bones.
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Choanal Slit
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Glottis and Hyoid Apparatus
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Anterior Respiratory Tree Anatomy
Laryngeal Mound
Glottis
Trachea with complete rings
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Tracheal Bifurcation/Syrinx
Trachea
Primary Bronchus
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Syrinx in an Adult Chicken
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Structure of Syrinx
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Syringeal Bulla from a Duck
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Bifurcation, Great Vessels, Interclavicular Airsac
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Syringeal Bulla
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Excised Lung
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Gross Appearance of Lungs
Turkey
Red-tailed Hawk
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Cut Lung Section with Opened Primary Bronchus
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Embedment of lungs in between ribs
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Cross Section at level of Heart
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Major Air Sac System
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Anterior and Posterior Thoracic Air Sacs
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Order of Branching

• Primary Bronchi
• Secondary Bronchi
• Parabronchi
• Atria
• Infundibuli
• Air Capillaries (site of gas exchange)

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Schematic of Avian Lung
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Atria and InfundibuliBranching off of Bronchus
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Electron Micrograph Air Capillaries
Blood flow is cross-current (I.E. at right angles
to direction of blood flow).
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Histological Section parabronchi, atria,
infundibuli and air capillaries
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Airflow in Paleopulmo and Neopulmo
The neopulmo does not constitute more thatn 25
of lung volume in any species significance is
uncertain.
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Air Flow Diagram
Accounts for c. 80 of air flow Two complete
cycles (4 strokes) necessary for a single bolus
of air to get in and out of the system
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Physiological Consequences

• Little mixing of inspired with expired gas
• End tidal CO2 levels are lower (c. 28 mm Hg for
  arterial CO2
• O2 concentration in arterial blood may exceed O2
  expired gas (normally c. 100 mm HG) - a feat not
  possible in an alveolar lung

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PhysiologicalDead Space
Note structure indicated by arrows. What is it?
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Dead Space Issue

• Physiological Dead space is calculated by

Bohr equation
Where a arterial, Eexpired air, Ppressure, V
volume
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Rewrite to Express in Terms of Dead Space Volume
Where F stands for a function of
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In terms of Minute Volumes
Where f frequency
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Substituting
Therefore, if respiratory rate (f) is reduced,
physiological dead space is also reduced.
Accordingly, birds have respiratory rates less
than 1/2 of that of a comparably-sized mammal
What consequences might this relationship have
with regard to anesthetic issue?
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Sinus Anatomy
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Clinical Applications

• Air sac cannulization
• Nebulization Therapy
• Respiratory Diseases
• Endoscopy

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Air Flow Diagram
Accounts for c. 80 of air flow Two complete
cycles necessary for a single bolus of air to get
in and out of the system
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Air Sac Cannulation Relief of Respiratory
Distress
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Air Sac CannulaAnesthetic Administration
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Nebulization Therapy
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Airway Blockages
Fungal Plaques Metaplastic Lesions Foreign Bodies
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AirSac Disease
Aspergillosis
Serratospiculosis
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Sinusitis
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Conclusions

• System serves same functions as in mammals
• Is more efficient
• Has unidirectional airflow
• Lungs are rigid airsacs function as bellows
• Unique disease problems and potential
• Unique considerations for anesthesia

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Sources of Information and Illustrations

• 1. McClelland, J. A Color Atlas of Avian
  Anatomy. Philadelphia. W. B. Saunders. 1991.
• 2. Koenig, HE. And HG Liebich. Antomie und
  Propaedeutik des Gefluegels Lehrbuch und
  Farbatlas fuer studium und praxis. Stuttgart,
  Schattauer, 2001.
• 3. Whittow, GC (ed). Sturkies Avian
  Physiology 5th ed. San Diego. Academic Press.
  2000.
• 4. Fudge, A. M. Seminars in Avian and Exotic
  Pet Medicine Anesthesia and Analgesia. J. C.
  Cornick_ Seahorn, Guest Editor. Vol 7 No. 1.
  January 1998.