2. GAS EXCHANGE/RESPIRATION IN BIRDS
The respiratory system of birds is complex and efficient. It consists of
External nares,
Pharynx,
Trachea
Air sacs
And lungs
3. External nares open into nasal passageways and pharynx.
Pharynx opens into trachea. Bones and cartilage support
the trachea.
A special voice box syrinx is present in the birds. It is
located where the trachea divides into bronchi. The
muscles of the syrinx and bronchi and properties or the
trachea produce bird vocalizations
4. The bronchi open into air sacs. The air sacs occupy much of
the body. They extend into some of the bones of the skeletal
muscles. The air sacs and bronchi connect to the lungs.
The lungs of the birds are made or small air tubes called
parabronchi. Parabronchi divides to form air capillaries.
These air capillaries are associated with capillary beds for gas
exchange.
5. MECHANISM OF RESPIRATION
MECHANISM OF RESPIRATION
Two factors are involved in inspiration and expiration:
1. Increasing and decreasing volume of the thorax
2. Alternate expansion and compression of air sacs occur
during flight and other activities. The movement of the sternum
and posterior ribs during breathing compresses the thoracic air
sacs. The contraction of flight muscles distorts the furcula.
Alternate distortion and recoiling compress and expand the air
sacs between the two shafts of bones.
6. VENTILATION
Cycle 1: air moves into the abdominal air sacs during
inspiration. Air is already present in the lung. This air moves into
the thoracic air sacs through parabronchi. The air in the thoracic
air sacs moves out of the respiratory system during expiration.
Now the air in the abdominal air sacs moves into parahronchi.
Cycle 2: at the next inspiration, the air moves into the thoracic
air sacs. It is expelled during expiration
7.
8. COMPARISON OF RESPIRATION IN BIRDS AND
TETRAPODS
The birds have a greater rate of oxygen consumption due to high metabolic rate. The
respiratory cycle in other tetrapods is a simple back-and-forth cycle. Ventilation does
not takes place during expiration. Thus much “dead air– remains in the lungs. But the
birds has unique system of air sacs and parabronchi. Thus, there is continuous
movement of oxygen-rich air over respiratory surfaces during both inspiration and
expiration. The quantity of “dead-air“ in the lungs is much lesser than other
vertebrates.
The respiratory system of birds is more efficient than other tetrapod. It supports high
in metabolic rates. Similarly, the oxygen tension is low at high altitudes.
The birds live and fly at high altitudes due to this efficient gas exchange system. Thus,
birds geese fly can reach the Himalayas at 9, 200 m during migrations.
