The LARYNX (voice box) contains the vocal cords. It is the place where moving air being breathed in and out creates voice sounds. The ESOPHAGUS is the passage leading from the mouth and throat to the stomach. The TRACHEA (windpipe) is the passage leading from the pharynx to the lungs. The RIBS are bones supporting and protecting the chest cavity. They move to a limited degree, helping the lungs to expand and contract. The trachea divides into the two main BRONCHI (tubes), one for each lung. These, in turn, subdivide further into bronchioles.
The RIGHT LUNG is divided into three LOBES, or sections. The left lung is divided into two LOBES. The PLEURA are the two membranes, that surround each lobe of the lungs and separate the lungs from the chest wall. The bronchial tubes are lined with CILIA (like very small hairs) that have a wave-like motion, just like in the nose. This motion carries MUCUS (sticky phlegm or liquid) upward and out into the throat, where it is either coughed up or swallowed. The mucus catches and holds much of the dust, germs, and other unwanted matter that has invaded the lungs and thus gets rid of it. The DIAPHRAGM is the strong wall of muscle that separates the chest cavity from the abdominal cavity. By moving downward, it creates suction to draw in air and expand the lungs. The smallest subdivisions of the bronchi are called BRONCHIOLES, at the end of which are the alveoli (plural of alveolus). The ALVEOLI are the very small air sacs that are the destination of air breathed in. The CAPILLARIES are blood vessels that are embedded in the walls of the alveoli. Blood passes through the capillaries, brought to them by the PULMONARY ARTERY and taken away by the PULMONARY VEIN. While in the capillaries the blood discharges carbon dioxide into the alveoli and takes up oxygen from the air in the alveoli, a phenomena known as “gas exchange“.