What do the bronchial tubes divide into within the lungs?

The bronchial tubes, also known as bronchi, are the larger air passages that branch off from the trachea and lead into each lung. Within the lungs, these bronchial tubes progressively divide into smaller branches known as bronchioles. The structure of the bronchioles is key to their function, as they continue to branch further and eventually lead to alveolar sacs, where gas exchange occurs.

Bronchioles are lined with smooth muscle, allowing them to regulate airflow in and out of the alveoli. This branching system is essential for increasing the surface area available for gas exchange, which is critical for efficient respiration. The other options, including alveolar sacs, capillaries, and veins, play roles in the respiratory and circulatory systems, but they are not the immediate structures that result from the division of bronchial tubes within the lungs.