Final answer:
The correct answer is option a. The trachea bifurcates into the right and left bronchi at the carina, a specialized ridge that also initiates a cough reflex when irritated. The bronchi are part of the bronchial tree, leading air to the lungs and ensuring the airways stay clear of debris.
Step-by-step explanation:
The trachea, commonly known as the windpipe, is an essential part of the respiratory system leading air into the lungs. When it reaches the point where it enters the lungs, the trachea bifurcates, or divides, into the right and left mainstem bronchi. This division occurs at a specialized location referred to as the carina. The carina is a ridge of cartilage at the base of the trachea where it splits into the bronchi. It's lined with a type of epithelium that is sensitive to irritation, thereby initiating a cough reflex if foreign material is detected.
The right and left bronchi then enter the lungs at an area called the hilum. Within the lungs, the bronchi continue to branch into progressively smaller tubes, constituting the bronchial tree, ultimately leading to the alveoli where gas exchange occurs. The epithelium inside the bronchi is equipped with cilia and mucus-producing goblet cells to trap debris and pathogens, which helps to maintain clean airways.