The alveoli
A)are supported by C-shaped cartilaginous rings.
B)are the primary site of respiratory gas exchange.
C)contract and relax,thereby determining resistance to air flow through the respiratory passages.
D)are composed primarily of smooth muscle.

Question

Quizplus · Accepted Answer

The alveoli, which are small air sacs in the lungs, are the primary site of respiratory gas exchange, where oxygen is taken up by the blood and carbon dioxide is released from the blood into the lungs. They are not supported by C-shaped cartilaginous rings, as the bronchi and trachea are. The alveoli do not contract and relax, and are not composed primarily of smooth muscle.

The Alveoli