1. AVIAN PHYSIOLOGY Respiratory System
Doç. Dr. Dr. Yasemin SALGIRLI DEMİRBAŞ
Resident ECAWBM (BM)

2. FUNCTIONS OF THE RESPIRATORY SYSTEM
Delivers oxygen from the air to the tissues and removes carbon dioxide.
Helps thermoregulation
Main differences: (1) Presence of air sacs and air spaces,
(2) Lungs structure,
(3) Unidirectional flow

3. PARTS OF THE RESPIRATORY SYSTEM
Parts in the head regions include the nasal openings, nasal cavities and the pharyngeal region of the mouth.
The cranial larynx (superior larynx or glottis), located in this pharyngeal region, is the opening to the trachea (windpipe).
The pharyngeal region also has the openings of the esophagus.
The cranial larynx is normally open to allow air passage, but it closes when feed is passing down the throat so that the feed goes down the esophagus and does not enter the trachea.

4. TRACHEA Trachea conducts air from the nares and mouth to the bronchi
Another functions of trachea: warming, moisturizing, and screening particulate matter from inspired gas.
Anatomically, significant differences exist between the avian trachea and the mammalian trachea.
Avian tracheal cartilages are complete rings unlike the incomplete C‐shaped rings of mammals.
The syrinx (or caudal larynx), located near the end of the trachea, is the avian's voice box.
Avians do not have vocal cords to produce sound. «Voice" is produced by air pressure on a valve and modified by muscle tension.

5. TRACHEA
The typical bird trachea is 2.7 times longer and 1.29 times wider than that of a comparably sized mammal - resistance to airflow through the trachea in birds is comparable to that in mammals .
Tracheal volume, is about 4.5 times greater than that of comparably sized mammals.
The impact of the larger tracheal dead‐space volume is reduced in at least three ways:
Birds have a relatively low respiratory frequency - minute tracheal ventilation rate is only about 1.5–1.9 times greater than that of comparably sized mammals
Tidal volume in birds is larger (about 1.7 times ) than that of a comparably sized mammal;
The large expansible volume and greater compliance of the respiratory system means that birds expend less energy when breathing compared with mammals
They are able to overcome any limitations imposed by the larger tracheal dead space.
birds have a relatively low respiratory frequency (approximately one‐third that of mammals) so that minute tracheal ventilation rate is only about 1.5–1.9 times greater than that of comparably sized mammals
tidal volume in birds is about 1.7 times larger than that of a comparably sized mammal;
the large expansible volume and greater compliance of the respiratory system means that birds expend less energy when breathing compared with mammals
They are able to overcome any limitations imposed by the larger tracheal dead space.

6. BRONCHI
Bronchial system of birds consists of only three orders of branching before the gas‐exchange surfaces are reached:
a primary bronchus (extrapulmonary and intrapulmonary),
secondary bronchi, and
tertiary bronchi, more commonly referred to as parabronchi:
They can be several millimeters long and mm in diameter (depending on the size of the bird)
Their walls contain hundreds of tiny, branching 'air capillaries' surrounded by a profuse network of blood capillaries.
Exchange of gases between the lungs and the blood occurs within these air capilleries.
Cross-current arrangement (Blood flows at right angles to parabronchi) increases amount of O2 entering blood.
After passing through the parabronchi, air moves into the ventrobronchi.

7. Comparison of avian and mammals respiratory system:
a) The avian 'unidirectional' respiratory system where gases are exchanged between the lungs and the blood in the parabronchi.
b). The mammals 'bidirectional' respiratory system where gas exchange occurs in small dead-end sacs called alveoli.

8. AIR SACS
The air sacs function as bellows, to ventilate the lungs with fresh air with higher O2 content during both inspiration and expiration.
The pulmonary air flow is continuous and unidirectional through respiratory cycle.
The air sacs is thin walled, about 10 times the volume of the lungs.
It situated between the internal organs in the thoracic and abdomen.
The air sac extend into the proximal bones of the extrimities, and the skull. Replacing bone marrow with air makes the bird lighter.
Histologically, the air sacs are poorly vascularized and do not significantly contribute to gas exchange

9. AIR SACS Most species of the birds have nine air sacs:
One interclavicular sac
Two cervical sacs
Two anterior thoracic sacs
Two posterior thoracic sacs
Two abdominal sacs
The volume of the air sacs is distributed approximately equally between the cranial and caudal groups.
During ventilation all air sacs are effectively ventilated, with the possible exception of the cervical air sacs, and the ratio of ventilation to volume is similar for each air sac.
Anterior sacs
Posterior sacs

10. BENEFITS Unidirectional flow of air Delivers huge quantity of O2
Remove lethal body heat
Protect internal delicate organs
Interclavicular sac is essential for vocal sound production

11. AVIAN RESPIRATION Avian respiration occurs in two cycles:
First inspiration: The air flows through the trachea and bronchi into the posterior air sacs.
First expiration: The air flows from the posterior air sacs to the lungs.
Second inspiration: Air flows from the lungs to the anterior air sacs.
Second expiration: The air flows from the anterior sacs back through the trachea and out of the body.

12. MECHANICS OF RESPIRATION
Birds do not possess a muscular diaphragm,
They depend on cervical, thoracic and abdominal muscles for inspiration and expiration,both of which are active processes requiring muscular activity
During inspiration: sternum moves forward & downward, vertebral ribs move cranially to expand the sternal ribs & the thoracoabdominal cavity.
This expands the posterior & anterior air sacs & lowers the pressure, causing air to move into those air sacs.

13. MECHANICS OF RESPIRATION
During expiration: The sternum moves backward & upward, vertebral ribs move caudally to reduce the volume of the thoracoabdominal cavity.
This reduces the volume of the anterior & posterior air sacs causing air to move out of sacs.

14. AVIAN RESPIRATION Conclusion:
takes 2 respiratory cycles to move 1 packet of air completely through
Advantages:
This maximizes contact of fresh air with the respiratory surfaces of the lung.
A bird replaces nearly all the air in its lungs with each breath.
No residual air is left in the lungs during the ventilation cycle of birds
By transferring more air and air higher in oxygen content during each breath, birds achieve a more efficient rate of gas exchange than do mammals