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How does the trachea divide into smaller airways inside the lungs?

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Medical illustration of the human chest showing the lungs, diaphragm, ribs, trachea, bronchus, and bronchioles, with one lung cut away to reveal internal structures. — human respiratory system The lungs serve as the gas-exchanging organ for the process of respiration.

The trachea, or windpipe, serves as the primary airway that facilitates the passage of air into the lungs. At its lower end, it divides in an inverted Y shape into two main stem bronchi, with one branch entering each lung.12

Once inside the lungs, these bronchi undergo a process of repeated subdivision to form an extensive airway tree. This branching occurs according to the rules of irregular dichotomy, where the trachea and subsequent airways give rise to daughter branches that may vary significantly in length and diameter. As these airways extend deeper into the lung tissue, they become progressively narrower, transitioning from bronchi into smaller, cartilage-free tubes known as bronchioles.31

On average, there are about 16 generations of division between the trachea and the terminal bronchioles, which represent the final purely conducting airways. Beyond this point, the airways transition into the gas-exchanging zone, where they eventually terminate in alveoli and alveolar sacs.34