Location and Structure of the Lungs
The lungs are a pair of elastic, spongy organs used in breathing. In humans the lungs take up a lot of the chest cavity. They are located just behind, and to either side of, the heart. They extend down from the collarbone to the diaphragm (the muscular wall between the chest cavity and the abdominal cavity). In adult humans each lung is 25 to 30 cm. long (10 to 12 in.) and roughly cone shaped. The right lung is somewhat larger than the left lung because it has three lobes, or sections, whereas the left lung has only two.
When we breathe, the air travels to the lungs through a series of tubes and passages. The air enters the body through the nostrils or the mouth. It travels down the throat to the windpipe. Inside the chest cavity the windpipe divides into two branches, called the right and left bronchial tubes that enter the lungs. The large bronchial tubes branch into ever smaller tubes, called bronchioles. These in turn divide into even narrower tubes. Each small tube ends in clusters of thin-walled air sacs, called alveoli. It is the alveoli that receive the oxygen and pass it on to the blood.