Respiration &Vocal Communication

Avian Lungs1. Respiratory System

– Delivers O2 and rids CO2

2. Thermoregulation– Evaporative Heat Loss

3. Vocal sound production

• (A). Dorsal view of the trachea (circled) and the lung of the Ostrich (Struthio camelus). The lungs are deeply entrenched into the ribs on the dorsolateral aspects (arrowhead). Filled circle, right extrapulmonary primary bronchus (EPPB). Note that the right EPPB is relatively longer, rather horizontal and relatively narrower compared with the left EPPB. Scale bar, 1 cm. (B) Close up of the dorsal aspect of the lung showing the deep costal sulci (s). Trachea, circled; filled circle, right extrapulmonary primary bronchus. Scale bar, 2 cm (Maina and Nathaniel 2001).

Avian lungs with uni-directional flowor “flow-through” ventilation

cf. Mammalian Lung Bi-directional flow

CervicalCervical

InterclavicularInterclavicular

AnteriorAnterior

PosteriorPosterior

AbdominalAbdominal

9 Airsacs Cranial• 1 interclavicular sac • 2 cervical sacs • 2 anterior thoracic sacs Caudal• 2 posterior thoracic sacs • 2 abdominal sacs

• Form and Function– Thin walled– Little vasculature– No gas exchange

– “Bellows”

Respiratory Pathway• Uni-directional, double cycle

• 1 - On first inhalation, air flows through the trachea & bronchi & primarily into the posterior (rear) air sacs

• 2 - On first exhalation, air moves from the posterior air sacs & into the lungs

• 3 - With the second inhalation, air moves from the lungs & into the anterior (front) air sacs

• 4 - With the second exhalation, air moves from the anterior air sacs back into the trachea & out

Inspiration

• the sternum moves forward & downward while the vertebral ribs move cranially to expand the sternal ribs & the thoracoabdominal cavity (see diagram below). This expands the posterior & anterior air sacs (see 1 above) & lowers the pressure, causing air to move into those air sacs. – Air from the trachea & bronchi moves into the

posterior air sacs &, simultaneously, – air from the lungs moves into the anterior air sacs.

Expiration

• the sternum moves backward & upward & the vertebral ribs move caudally to retract the sternal ribs & reduce the volume of the thoracoabdominal cavity. The reduces the volume of the anterior & posterior air sacs (see 2 & 4 above), causing air to move out of those sacs.

• Air from the posterior sacs moves into the lungs &, simultaneously,

• air from the anterior sacs moves into the trachea & out of the body.

Parabronchus

• arrows – d. of airflow• a – arterial blood• v – venous blood• * - atria• arrowhead –

infundibulum• m – mantle of gas

exchange tissue– air capillaries– blood capilaries

• Top: Schematic of air flow (large arrows) and blood flow (small arrows) patterns constituting the cross-current gas-exchange mechanism operating in the avian lung. Note the serial arrangement of blood capillaries running from the periphery to the lumen of the parabronchus and the air capillaries radially departing from the parabronchial lumen. Bottom: Pressure profiles of O2 and CO2 from initial-parabronchial (PI) to end-parabronchial values (PE); and in blood capillaries from mixed venous (Pv) to arterial blood (Pa). The PO2of arterial blood is derived from a mixture of all serial air-blood capillary units and exceeds that of PE. In mammals, the PaO2 cannot exceed that of end-expiratory gas (i.e., PE) (Brown et al. 1997).

air capillary

rbc

light

TEM

surfactant layer<0.2μm

Trachea

The Syrinx