Anatomy of the Lungs and Air Passages
The respiratory system—lungs and air passages—provides the body with a continuous supply of oxygen and a means of removing carbon dioxide. The oxygen we inhale passes from the lungs to the bloodstream, which carries it to cells throughout the body. At the same time, blood picks up carbon dioxide and returns it to the lungs to be exhaled.
The diaphragm and chest muscles are used to expand and contract the lungs during breathing (respiration). The trachea (windpipe) branches into two primary tubes (bronchi), one leading into each lung. Each of these bronchi divides into progressively smaller bronchi, which branch into thousands of bronchioles, culminating in millions of tiny air sacs (alveoli). The alveoli are covered with tiny blood vessels (capillaries), where exchange of oxygen and carbon dioxide occurs.
The lung on the right side of the body has three lobes; the left lung has only two. Both lungs are covered with a layer of moist membranes, called the pleura, which allows them to inflate and deflate smoothly.