Question

Describe the complete path of air through bird lungs. Why does it take two cycles of breathing to move a molecule in the air through this system?

Answer 1

In birds air flow is unidirectional.

The respiratory system of birds consists of lungs and air sacs connected.

The exchange of gases takes through the static surface on lungs.

Complete inhalation and exhalation takes two cycles

First air inhaled through nostrils it travels through the trachea then splits into left and right primary bronchi or mesobronchi,each bronchus leading to a lung.

The inhaled air reaches primary bronchus and some air enters the lungs where gas exchange occurs, while the remaining air fills the posterior air sacs.

Then, during the first exhalation, the fresh air in the posterior sacs enters the lungs and undergoes gas exchange. The spent air in the lungs is displaced by this incoming air and flows out the body through the trachea.

In second inhalation, fresh air again enters both the posterior sacs and the lungs. Spent air in the lungs is again displaced or replaced by incoming air.

The air cannot come out through trachea because fresh air is flowing inward.

The spent air from the lungs enters anterior air sacs. In second exhalation, the spent air in the anterior sacs and lungs flows out through trachea and fresh air from posterior sacs enters the lungs for gas exchange.

Thus the exchange of gas is complet in two cycles.