Structural Features

The major parts of the respiratory system are the lungs, trachea, larynx, nose, mouth, bronchi, bronchioles and alveoli. Air travels through the nose or mouth and passes into the pharynx (throat). The air then moves down the trachea (windpipe) and separates into two tubes known as bronchi. Epithelial cells that line the bronchi and trachea secrete mucus. Cilia is found on many epithelial cells, they filter out foreign materials and move mucus. The bronchi branch out into many bronchioles. Each bronchiole separates in to a number of alveoli; small sacs of air designed to accommodate gas exchange.