Which of the following structures is primarily responsible for respiration in the lungs?

• A. Bronchi
• B. Respiratory bronchioles
• C. Trachea
• D. Alveoli

Answer: (B)

The primary structure responsible for respiration in the lungs is the alveoli. These tiny air sacs are the site of gas exchange, where oxygen from inhaled air diffuses into the blood while carbon dioxide from the blood is released into the air to be exhaled. The alveoli have a large surface area and are surrounded by a network of capillaries, facilitating efficient gas exchange.

Respiratory bronchioles, although they play a role in the respiratory process as they transition from conducting airways to areas of gas exchange, are not the main sites for the actual exchange of gases. Instead, they lead to the alveolar sacs where this critical exchange occurs.

In addition, the bronchi and trachea serve primarily as conducting airways, transporting air to the lungs but not directly involved in the exchange of gases. Their structures support airflow but do not facilitate the actual respiration process that occurs within the alveoli. Understanding the specific role each structure plays in respiration helps clarify the mechanics of pulmonary function.