Final answer:
The hilum is the structure where the bronchi, pulmonary vessels, lymphatic vessels, and nerves collectively pass into each lung, forming the bronchial tree that serves as a passage for air and supports gas exchange within the alveoli.
Step-by-step explanation:
The structure through which the bronchi, pulmonary vessels, lymphatic vessels, and nerves collectively pass into each lung is known as the hilum. The hilum is a concave region on the mediastinal surface of the lungs and serves as a critical entry and exit point for these structures. Each primary bronchus divides into smaller bronchi and bronchioles as it enters the lungs, forming a bronchial tree. This tree-like structure of the respiratory system ends with the tiniest branches called bronchioles which terminate in sacs known as alveoli; this is where the exchange of gases occurs with the blood.
Air enters the lungs through the main bronchi which then keep branching into smaller and smaller passages until becoming the narrow bronchioles. These passages along with associated blood vessels and nerves are essential for the pulmonary system's functionality, providing a passage for air and supporting the gas exchange process within the alveoli.