Avian Respiratory

• Avian respiratory system

  • Inelastic lungs
  • Volume not changed during respiration
  • Relative volume of trachea much larger
  • Gas exchange occur in air capillaries rather than having alveoli
  • Movement of ribs and sternum changes abdominal pressure moving air in and out of the air sacs (due to lack of diaphragm)
  • Tracheal volume 4.5 X larger than in mammals
  • Longer and wider trachea creating a larger dead space

  
• Parabronchi/tertiary bronchi

  Site of gas exchange
• Paleopulmonic

  • Parallel tubes extending from secondary bronchi
  • Gas flow is unidirectional
• Neopulmonic

  • Irregular branching system
  • Gas flow is bidirectional
  • Poorly vascularized
  • Thin membranous structures
  • Do not participate in gas exchange
  • Gas exchange occur in the parabronchi
• Air sacs

  • 9 air sacs (4 paired and 1 unpaired)
  • Cranial group (Consists of paired cervical and cranial thoracic air sacs and unpaired clavicular air sac)
  • Caudal group (Paired caudal thoracic and paired abdominal air sacs)

  
• Inspiration

  1. Sternum moves cranially and ventrally as coracoids and furcula (wishbone) simultaneously rotate forward at the shoulders

  2. Sternal ribs move cranially laterally expanding the sternal ribs and thoracoabdominal cavity

  3. As thoracic cavity expands, volume and pressure inside the air sacs decrease causing air to move caudally through the intrapulmonary bronchus

  4. Half of the air goes through the neopulmonic lung continuing to the caudal thoracic and abdominal air sacs

  5. Other half goes to the mediodorsal secondary bronchi and the paleopulmonic parabronchi
• Exhalation

  1. Contraction of expiratory muscles decreases volume of the thoracoabdominal cavity causing air to flow out of the caudal thoracic and abdominal air sacs

  2. Gas passes through the neopulmonic to the paleopulmonic lungs
• Unidirectional gas flow

  All air moves through paleopulmonic parabronchi in caudo-to-cranial direction while traveling through the parabronchi bidirectionally
• Bird eggs contain all the nutrients necessary for embryonic development except oxygen
• Oxygen passively diffuses into the egg pores found in the eggshell while carbon dioxide diffuses out of the same pores
• Normal chicken egg has 10,000 pores
• Prenatal period

  Capillaries located in chorioallantoic membrane function in gas exchange across the shell and its associated shell membranes
• Internal pipping

  1. Chick's beak penetrates the internal shell membrane

  2. Allows the chick to begin pulmonary respiration using air located in the air cell

  
• External pipping


  1. Chick's beak penetrates the eggshell

  2. Chick is able to receive sufficient oxygen to complete the hatching process