Now, if we check out this structure, which are basically these saclike structures where gas exchange actually takes place within the alveoli of our lungs, we have specialized immune cells known as the alveolar macrophages. And these are specialized cells that can engulf and digest any harmful agent and substance that the cell actually comes across. Now, we also have something called airway constriction. So if we examine our air passageways, we have trachea, we have the bronchi, we have these bronchioles, these are lined with our muscles. And these muscles can actually constrict. And when they constrict, they create a more narrow system of canals and that basically decreases the likelihood that our contaminant or harmful substance will pass into our body via our alveolar.