Which of the following structures arises from the trachea and enters the hilum of the lungs?

The primary bronchi are the structures that arise from the trachea and enter the hilum of the lungs. The trachea bifurcates at a point known as the carina into two primary bronchi, one for each lung. These primary bronchi then enter the hilum, which is the part of the lung where blood vessels, nerves, and bronchi enter and exit.

At the hilum, the primary bronchi further divide into secondary bronchi, which are responsible for delivering air to each lobe of the lungs. This anatomical pathway is crucial for ensuring that air can reach the alveoli, where gas exchange occurs. Understanding the organization and branching of the respiratory system is essential for comprehending how air flows into the lungs and the overall mechanics of respiration.