The lungs are connected to the end of the trachea within the ribcage. They contain bronchi that help carry air, humidify the oxygen and filter out any unwanted particles. The lungs also contain mesobronchus that carry oxygen to the air sacs.

The trachea is a long tube that runs alongside the esophagus in the neck. It carries oxygen from the oral and nasal cavity to the lungs. The trachea contains ciliated cells that help filter out unwanted particles.

• Trachea-opening to trachea is the glottis

• 2 lungs

• 9 air sacs

  • • • 2 cervical sacs

      • 1 interclavicular

      • 2 anterior thoracic air sacs

      • 2 posterior thoracic air sacs

      • 2 abdominal air sacs

• Syrinx

• Intercostal

• No diaphragm

The lungs and air sacs allow a continuous stream of air to pass through the tissues in one direction. A pair of air sacs is found in the abdominal cavity lying dorso-laterally to the intestines. Additionally, two pairs of air sacs can be found in the cranial and caudal thorax. Both penetrate into the septum. The avian respiratory system is extremely efficient. There is no diaphragm and the intercostal muscles are the major muscles for respiration while expiration is the result of contracting abdominal muscles. There are no sweat glands in birds so the respiratory system is also used for cooling.

• Birds lack a diaphragm

• Birds inhale by lowering the sternum relative to the spinal vertebrae, enlarging the chest cavity and expanding the air sacs.

• Contraction of the sternum and ribs compresses the air sacs, pushes fresh air from them through the lungs, and exhales the air

• 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, as it is in mammals.

• The unidirectional movement of a single inhaled volume of air (shown in blue) through the avian respiratory system.

• One volume of air moves sequentially into the posterior air sacs, into the lung, and into the anterior air sacs and is then exhaled.

• Two full respiratory cycles—inspiration, expiration, inspiration, and expiration—are required to move one volume of air through its complete path.