Respiratory organs of birds

Birds have two lungs connected to a trachea and ventilated by an aspiration pump (https://sumit012001.blogspot.com/2020/03/respiration-process-in-mammals.html ) . Lungs are paired  , pink coloured , saccular , non elastic spongy organs of respiration .

STRUCTURE :

v The trachea is divided into two primary bronchi , ( = mesobronchi ) that do not enter the lung but extend posteriorly to reach the posterior air sac .

v Along the way , the primary bronchi give rise to numerous branches , the most prominent of which include latero ,ventro, and dorso bronchi as well as secondary bronchi . These leads to the parabronchi ( Figure – 11.36 a – c )

vThe wall of the parabronchi consists of an anastomosing network of air capillaries , each only a few thousands of a millimeter in diameter , surrounded by blood capillaries . It is the lining of the air capillaries that constitutes the respiratory epithelium .

v During passage through the parabronchus , gases diffuse between the lumen  of the parabronchus and the connecting , blind – ended air capillaries . Oxygen diffuse in turn from the air capillaries into the adjacent blood capillaries that give up carbon dioxide to the air capillaries. Thus the walls of air and blood capillaries constitute the sight of gas exchange .

AIR SAC :

v Nine avascular air sacs are connected to the lungs .

v Generally , the anterior air sacs include the single interclavicular sac and the paired cervical and anterior thoracic air sacs .

v The posterior air sacs include the paired posterior thoracic and paired abdominal air sacs ( Figure – 11.35 a )