What small structures in the respiratory system are responsible for gas exchange with surrounding capillaries?

• A. Bronchi
• B. Tree alveoli
• C. Alveoli
• D. Tracheae

Answer: (C)

The small structures in the respiratory system responsible for gas exchange with surrounding capillaries are the alveoli. These tiny air sacs are located at the end of the bronchioles and provide a large surface area for gas exchange to occur. Their walls are extremely thin, allowing oxygen to diffuse across into the blood in the capillaries while carbon dioxide diffuses from the blood into the alveoli to be exhaled. This efficiency in gas exchange is critical for maintaining proper oxygen levels in the body and removing waste gases.

In contrast, the bronchi and tracheae are parts of the airway that serve primarily as passageways for air to enter and exit the lungs but do not participate directly in gas exchange. The term "tree alveoli" may refer to the branching structure of the alveoli as they resemble clusters of grapes, but it is not a standard term used in respiratory physiology. Therefore, alveoli are the specific structures directly involved in the gas exchange process.