Question

In birds, which organ gets inflated on inspiration?
A. Lungs
B. air sacs
C. Air capillaries
D. All the above

Answer 1

Hint: Birds are able to fly and their body is adapted for this activity. Forelimbs of birds are modified into wings. Body of birds is lightweight which helps them to fly. For respiration, lungs are found in them.

Complete answer: The respiratory system of birds is complex and well developed than other vertebrates. In order to fly, birds require more oxygen. Lungs of birds are small and to increase their surface area, air sacs are present. In birds, expiration is more active than inspiration. The respiratory tract of birds includes external nares, internal nares, glottis, larynx, trachea, syrinx and bronchi. Through the respiratory tract, air enters inside the lungs and from lungs enters into air sacs. Bronchioles are absent in birds but air capillaries are found. Air sacs are large non-muscular and non-vascular sacs. These originate from secondary bronchioles. The volume of air sacs is more than the lungs. These act as an accessory respiratory organ and are covered by peritoneum. During respiration, intercostal muscles constrict and ribs lift upside. The volume of thoracic and abdominal cavity increases and air enters into air sacs through the respiratory tract. Air sacs become inflated and lungs constrict. During expiration, thoracic and abdominal muscles constrict. Air is forced out from air sacs, thus it constricts and the lungs become inflated.
Hence, the correct answer is option B.

Note: Air sacs do not take part in the process of gas exchange. During inspiration, when sacs get inflated provide buoyancy to the bird for flying. Air sacs maintain body temperature. These act as a cooling device.