The brain and its respiratory tree are responsible for every one of the approximate 6,000,000 breaths a human takes each year. Another name for the lungs and its system of gas exchange, this bronchial network both delivers oxygen to the bloodstream and takes carbon dioxide out. Though some think the lungs are merely giant balloons in the chest, it really contains ducts and tiny alveolar sacs that, if separated into its various parts, would cover the same area as a small house.
Air travels into the respiratory tree via the mouth and nasal passages, then into the trachea, also known as the windpipe. This long tube extends down the throat just in front of the tube, carrying food to the stomach, the esophagus. The air is sucked in instinctively when the lungs' alveolar sacs have been emptied of carbon dioxide and attempt to fill again with oxygen, aided by the diaphragm below the lungs dropping slightly.
The respiratory tree, also known as the tracheobronchial tree, branches at the bottom of the trachea, at a forked membrane called the carina. Here, two bronchus tubes lead into each lung, where more branching ensues into the lobar bronchus and smaller segmental bronchus that resemble the limbs of a tree. Smaller sticks on those branches could then be considered terminal bronchiole, where alveolar ducts and attached sacs make up what would amount to the flowers and seeds of a real tree.
Inside the nose and various tubing of the respiratory tree are millions of hair-like fibers known as cilia. These help to clean the oxygen of impurities before reaching the blood capillaries in the alveolar sacs. They also help the lungs to sweep clean any mucus that has formed inside, created for the purpose of removing those impurities. While blood cells take on oxygen in the alveoli, they also drop off the carbon dioxide waste from the body's other cells.
Aside from providing the right amount of oxygen to the body's cells, the respiratory tree has other functions. It regulates the temperature of the air, while serving as an impromptu humidifier. It also has ties to a person's sense of smell as well as the urge to sneeze or cough to clear foreign matter. While other disorders can cause problems with gas exchange, perhaps the most nefarious violator is smoking, which can lead to damaged cilia, excessive clogging of the alveoli, reduced oxygen intake and even cancerous growths.