The lungs are vital organs located in the chest (thoracic) cavity of the human body. They function in gas exchange by obtaining oxygen from the air to provide energy for cells throughout the body and by eliminating carbon dioxide. Air enters through the nasal cavities, travels into the main airway (called the trachea) and then into the lungs. There are two lungs. The left lung is smaller (to accommodate the heart), while the right lung is slightly larger. The trachea branches into the bronchi, which are tree-like tubes that connect to each lung. The bronchi branch further into smaller passageways called the bronchioles, which lead to the alveoli. The alveoli are sac-like structures (that look like clusters of grapes on a stem) where gas exchange occurs. Unlike the trachea, the bronchioles can be recognized by an absence of cartilage. Pulmonary arterioles are blood vessels that travel juxtaposition to...