The bronchi are the top part pf the lungs, made out of cartilage. They divide from the trachea, each lung having its separate bronchi. The bronchi further divide into bronchioles, which are smaller versions of the same thing, just branching off into different directions within the lung. The function of the bronchi and bronchioles is to create passageways for air throughout the whole main organ. the bronchioles spread all the way to the membrane of the lungs, transporting clean, moist, and warm air. At the tips of the bronchioles are alveoli. These are buds entirely covered by blood vessels to increase surface area. This is where the actual gas exchange between the blood and the lungs take place. The gases pass by the process of diffusion between the alveoli sacks and their blood vessels, and the blood stream. There are about 300 million alveoli in both lungs, and this amount is used to increase the speed with which the gas exchange takes place. The alveoli is the place of action in the respiratory system.