The bronchi are the large air passages that branch off from the trachea, or windpipe, and lead into the lungs. They play a crucial role in the respiratory system by allowing air to flow in and out of the lungs. Each bronchus divides into smaller branches called bronchioles, which further distribute air throughout the lung tissue. These structures are lined with mucus and tiny hair-like projections called cilia, which help trap dust and germs, keeping the lungs clean. When we breathe, the bronchi expand and contract, ensuring that oxygen reaches the alveoli, the tiny air sacs where gas exchange occurs.