Your two lungs are the main organs of the respiratory system filling most of your chest. Lungs rely on your rib muscles and the diaphragm to expand and deflate. Air travels down your trachea into two bronchi, dividing into bronchioles and then into the millions of lung cells called alveoli. These clusters of tiny airbags provide a tennis-court sized area to maximize gas exchange. This is where the magic happens, where oxygen from the air is absorbed and passes into your blood. Carbon dioxide, a waste product of metabolism, travels from the blood to the alveoli, where it flows out and is exhaled.
Alveoli is a word taken from Latin meaning “little cavity”. So the lungs are in effect an enormous cavity enabling us to breathe. The lungs are covered by a thin layer of tissue, the pleura, and by lubricating fluid which allows smooth expansion and contraction.
There are many types of lung cells. Type 1 epithelial cells, or squamous alveolar cells, form most of the alveoli. They are devoid of organelles, such as mitochondria and golgi bodies, and have incredibly thin walls for effective gas exchange. Type 2 epithelial cells are cuboidal in shape and produce a surfactant to keep the alveoli moist. The lungs also have alveolar macrophages that provide a defensive mechanism against microbes and other harmful substances we breathe into the lungs. If this seems like a lot to take in, just take a deep breath and cherish your magnificent lungs!