MEDICAL ANIMATION TRANSCRIPT: Your lungs are two spongy organs in your chest. The left lung is divided into two lobes or sections, and the right lung has three lobes. When you breathe in, air enters your nose or mouth and passes into your trachea or windpipe. At the carina, the trachea divides into two bronchi, then branches into smaller bronchioles. The bronchioles end in tiny air sacs or alveoli. Here, the oxygen in the air you inhale passes into the bloodstream and carbon dioxide from your body passes out of the bloodstream. The carbon dioxide is expelled from your body when you exhale. Your lungs are encased by pleura, a thin membrane that protects them and helps them slide back and forth as you breathe in and out. Underneath your lungs is the diaphragm, a smooth, thin muscle that helps your lungs expand and contract as you breathe. Your lungs are connected to small collections of immune system cells called lymph nodes, by way of lymphatic vessels. You have groups of these lymph nodes near your lungs, above your collar bones, and behind your breastbone, as well as in other parts of your body. The lymphatic vessels carry bacteria, cancer cells, and other unhealthy material away from your lungs and other organs in a clear fluid called lymph. Lymph nodes filter this material out of the lymph. Lung cancers most commonly start in the bronchi, but they can also begin in the trachea, bronchioles, or alveoli.