pneumonia
Meaning of pneumonia: Bacteria, viruses, fungi, inhaled material and radiation can all produce pneumonia, so the name describes a pattern of lung injury rather than one illness.
Definition of pneumonia
Pneumonia is inflammation of the lung tissue in which the alveoli, the tiny air sacs where oxygen and carbon dioxide cross into and out of the blood, fill with fluid or pus instead of air. That filling blocks part of the exchange surface, so less oxygen reaches the bloodstream. It may involve one small area or spread through both lungs.
What causes it?
Infection is the usual cause but not the only one. The cause is worth naming because these groups behave differently and are recognized in different ways.
| Cause | What it involves |
|---|---|
| Bacterial | The most common cause of pneumonia severe enough to need hospital care |
| Viral | Often follows an upper respiratory illness, and a bacterial infection can then follow it |
| Fungal | Mainly affects people whose immune defenses are weakened |
| Aspiration | Food, drink, saliva or stomach contents drawn into the airway instead of swallowed |
| Radiation | Inflammation of lung tissue that lay inside a treated field |
| Inhaled irritants and immune reactions | Chemicals and dusts, or repeated exposure to an inhaled substance the immune system reacts against |
How is it grouped?
Two labels appear constantly. The first records where the infection was picked up, because that shapes which organisms are likely: community acquired pneumonia begins outside a healthcare setting, while hospital acquired pneumonia develops during an admission and tends to involve organisms that resist more drugs. The second describes the pattern inside the lung. Lobar pneumonia fills one distinct lobe. Bronchopneumonia is patchy and scattered around the small airways. Interstitial pneumonia thickens the tissue between the air sacs rather than flooding them, and is more typical of viral causes. A single scan can show more than one pattern at once.
Why does it affect breathing?
Air normally meets blood across an extremely thin barrier inside the alveoli. When that space fills, blood keeps flowing past sacs that hold no air, so it returns toward the heart without collecting oxygen. Widespread filling therefore drops the oxygen level in the blood, while the inflammation itself produces fever, cough and faster breathing. Confusion, low blood pressure and a racing heartbeat point toward more severe illness. Older adults sometimes show those changes with very little cough, which is one reason the illness can be missed in that group.
How is it told apart from bronchitis?
| Pneumonia | Bronchitis | |
|---|---|---|
| Where it sits | Air sacs and the tissue around them | Lining of the larger airways |
| Chest imaging | Shows an area of filling | Usually clear |
| Oxygen level | Can fall | Usually holds |
Used in a sentence
The chest x-ray findings were consistent with pneumonia in the lower portion of the right lung.
Good to know
Pneumonia involves fluid or pus filling the alveoli, which separates it from bronchitis, an inflammation confined to the larger airways, and from pleurisy, which affects the lining around the lung rather than the lung tissue itself.
Word origin
Where “pneumonia” comes from
Formed from Greek pneumon, meaning lung, and the suffix -ia, indicating a condition.