How are primary bronchi structured compared to bronchioles in terms of cartilage?

Primary bronchi are distinguished by the presence of cartilage, which provides structural support to maintain their open airway, allowing for efficient airflow from the trachea into the lungs. This cartilage is organized in C-shaped rings or plates that prevent the bronchi from collapsing under pressure and during respiration. As the airways branch into smaller passages, they transition into bronchioles, which do not contain cartilage. Instead, bronchioles have smooth muscle and elastic fibers, allowing them to regulate airflow and resistance through constriction and dilation. The lack of cartilage in bronchioles is crucial for their flexibility and adaptability in response to changes in breathing patterns, highlighting the functional differences in the respiratory system.