The lungs function to bring air in contact with blood so that oxygen can be added to the body and carbon dioxide removed. They are two cone-shaped, spongy organs that fill your chest cavity. They extend from the bottom of your chest to a point slightly above the collar bone, and they lie against your ribs. The back surface of each lung is curved to allow room for the heart and for your esophagus, trachea, nerves, and the blood vessels of your chest.
One way to imagine what your breathing passages and lungs look like is to think of an upside-down tree covered by two balloons. The trunk of the tree would be similar to the trachea. The trachea (windpipe) carries air from the outside into your lungs much as a tree carries nutrients from the ground to other parts of the tree. The trachea divides into two main branches known as the left and right main stem bronchi. These main stem bronchi are the actual passages for air moving to and from each lung. The bronchi continue to divide into smaller tubes called bronchioles that eventually end in little air sacs called alveoli, which resemble a microscopic bunch of hollow grapes. It is at the level of the alveoli, the tiny air sacs, where the oxygen you breathe in goes into the blood and the carbon dioxide that your body has produced is exhaled.
The left lung is partially divided into two lobes, the upper and lower. The right lung is divided into three lobes, the upper, middle, and lower.