Pneumonia occurs when there is an inflammation of the bronchioles and alveoli, and may be either infectious, or non-infectious.
Non-infectious Pneumonia is caused by aspiration of toxic/irritating gasses or gastric juices, that cause inflammation.
Infectious Pneumonia is caused by microbes such as bacteria, viruses, fungi, protozoa, etc.
Pathophysiology
The respiratory tract in a healthy individual is sterile. So when we have a microbe/foreign substance that makes it past the body's natural expulsion mechanisms such as sneezing, or swallowing, we see an inflammatory immune response. Pathogens etc are quickly phagocytised By resident macrophages in the alveolus, before the inflammatory/immune defences attack.
I would like to point out that infection elsewhere in the body may travel through the blood stream and end up in the lungs, where bacteria may reap havoc.
The inflammatory/immune response however damages the bronchial and alveolus membranes, which we then see result in even more inflammation. This bodily response as well know encouraged odema, which will be present.
We will also see interference with the gas exchange, as exudate and infectious debris fill the alveoli, impairing normal breathing.
We have 4 kinds of Pneumonia:
1. Lobar pneumonia
2. Bronchopneumonia
3. Interstitial Pneumonia
4. Millary Pneumonia
Might add to this later if I get time