Full Lungs and Respiratory System of the Chest (Posterior View) Description
[Continued from above] . . . through the windpipe, or trachea. It divides into two branches that enter the lung cavities. The lining of the trachea has mucus and hair like fringes that keep the lungs and air passages free. At the end of the trachea, each lung has a bronchus, which is the air passage into the lungs. There are also respiratory membranes such as the alveoli. Through the thin walls of each alveolus, oxygen is inhaled and absorbed into the bloodstream.
The respiratory system is mainly contained in two lungs. The right lung has compartments that process the oxygen in the air to be released into the blood and expel carbon dioxide, which is exhaled through the nose and mouth. The left lung cavity encloses the heart, which processes the oxygenated blood and returns deoxygenated blood into the lungs for exhalation.
Within the upper abdomen, the lungs are enclosed in a kind of cage in which the ribs form the sides and the diaphragm, an upwardly arching sheet of muscle, that forms the floor. The diaphragm plays a very important role in the breathing process. When a breath is taken, the diaphragm is drawn downward until it is flat. At the same time, the muscles around the ribs pull them up like a hoop skirt. The chest cavity becomes deeper and larger, making more air space. There are openings in the diaphragm for the esophagus, the phrenic nerve (which controls the movements of the diaphragm to produce breathing), and the aorta and vena cava blood vessels, which lead to and from the heart. When air is drawn into the lungs, the muscles in the diaphragm contract, pulling the central tendon down. This enlarges the chest, and air then passes into the lungs to fill the larger space.
Breathing is an automatic process, which comes from the brain stem and is so strong a force that the involuntary reflexes will not allow us to stop breathing for any length of time. The passageways in the respiratory system are lined with various types of epithelia to prepare the air properly for utilization and with hair-like fibers called cilia that move in a wave-like motion to sweep debris out of the lungs for expulsion.