The respiratory system is not a perfect well oiled machine, it too has its ups and downs. When problems occur, the lungs or other parts of the respiratory system can get infected. An example of an infection is pneumonia. Pneumonia is an infection started by a virus, bacteria, or any other small pest. Once one of these substances enter the lungs, the immune system starts sending in fluid to help flush out the source of the problem. However the spreading does not just stop, especially for bacteria. Once the fluid comes in, the bacteria starts growing rapidly. The lungs are warm, dark, and wet, a perfect breeding ground for bacteria, and when more liquid comes in, it's like a frenzy. Now, your lung is filled with microorganisms and fluids. You now feel a thick substance in your lungs and constantly cough to get it out. The only way to do so is with antibiotics and time. Antibiotics will kill any bacteria started pneumonia, but viruses can only go away with time, because there is no way to kill a virus with medicine. eventually all of your fluid will leave, including the root cause, showing you the strong connection between the respiratory and immune system.
The picture to the right is an example of a pair of lungs with pneumonia.
The picture to the right is an example of a pair of lungs with pneumonia.
Links about Pneumonia and its treatment-
http://www.mayoclinic.com/health/pneumonia/DS00135