What is pneumonia? Pneumonia is an infection that causes the air sacs in the lungs to become inflamed and sometimes full of liquid. The word pneumonia was coined in 1603 and it comes from the Greek “pneumon”, which means lung.
Pneumonia is caused when viruses, bacteria, or other microorganisms infect the lungs. It is a very common illness and it is estimated to affect 450 million people a year. Of those, roughly 4 million a year die, but they tend to be the very old, or people who are already suffering from another illness. If you are healthy and have access to antibiotics, it is an eminently survivable illness. Because many of the people who are killed by pneumonia are old, it has been known as “the old man’s friend”. It shortens their suffering in a painless way. It was given that name by a Canadian doctor called Sir William Osler, who has been called the Father of Modern Medicine.
There is no one single cause of pneumonia, which sometimes makes it tricky to treat. It can be caused by bacteria, viruses, fungi, and even parasites. However, it is most commonly caused by bacteria and viruses, and of those there are some that are more common than others. The most common bacteria is Streptococcus pneumoniae, which causes about 50% of cases. Viruses cause about 15% of cases, and these can be viruses like the corona virus.
For pneumonia to happen, the bacteria, virus, or fungus has to get down into the lungs. Our bodies have a lot of different systems to stop that happening. The saliva in our mouths and the hairs and mucus in our noses are the first line of defense. Then we have the tonsils. Any bacteria that make it past there are likely to get pulled down into the stomach with our saliva or the food we eat and the liquid we drink. Depending on how well hydrated we are, we swallow about 1 liter of our own saliva every day. However, some bacteria can make it down the trachea. Even then there are layers of mucus to stop them doing any damage, but they can go right down into the bottom of the lungs.
Our lungs are a series of connected tubes that end in approximately 480 million tiny balloons called alveoli. Each alveoli has blood capillaries that run through it. When we breathe in, the alveoli inflate with air and the oxygen passes out of the air into the blood. At the same time, carbon dioxide passes out of the blood into the alveoli, keeping them inflated, and then they empty when we breathe out. Without them, we obviously cannot breathe.
When the viruses or bacteria reach the alveoli, they attach themselves to the walls and start to replicate. This triggers an immune response from the body, which is where the problems come from. The bacteria and the viruses can cause lung damage on their own, but it is our own immune system that causes all of the symptoms and difficulty breathing that are associated with pneumonia. When we get a bacterial or viral infection, the first step is for the body to send cells to make the area swell up. The idea is to release fluid out of blood capillaries into the surrounding flesh to trap the invaders and to give the white blood cells room to work. Generally, this is a good strategy, but when your lungs are infected and the blood capillaries release fluid to swell up, that fluid ends up filing the alveoli and making it impossible to breathe. The white blood cells that die while killing the bacteria or virus also end up as pus inside the alveoli. When our immune system detects bacteria or viruses, we get a fever, which is one of the symptoms of the pneumonia. The fever raises the body’s temperature to make it inhospitable to the invaders. We also get a cough because the lungs are filling with fluid and the body’s reaction to that is to try to cough up as much of the fluid as possible. Shortness of breath is the third symptom which happens because the lungs are filling with fluid and the passage of oxygen and carbon dioxide is limited to the alveoli that are not liquid filled.
Some things, such as smoking, can increase the risk of getting pneumonia because it reduces the functionality of the lungs. Pneumonia can be detected in an X-ray. The parts of the lung that are full of fluid are much denser than the rest of the lungs and that makes them appear white on an X-ray. In the majority of people, their immune system can destroy the virus or the bacteria. Sometimes antibiotics are necessary, but once the infection is gone, the fluid in the alveoli goes away and breathing can go back to normal. The problem is with elderly people whose immune system is not as effective as a younger person. Also, people who are suffering from other illnesses might not be able to shift the pneumonia. If the lungs fill with fluid, breathing becomes difficult and a prolonged lack of oxygen can lead to many other problems, including organ failure and death. This is why pneumonia is the ultimate cause of death for many people who are sick with other illnesses. And this is what I learned today.
Photo by Polina Tankilevitch: https://www.pexels.com/photo/person-holding-thermometer-3873188/
Sources
https://my.clevelandclinic.org/health/symptoms/21660-inflammation
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https://www.mayoclinic.org/diseases-conditions/pneumonia/symptoms-causes/syc-20354204
https://www.healthline.com/health/elderly-pneumonia#symptoms
https://www.healthline.com/health/alveoli-function#alveoli-function
https://www.sciencedaily.com/releases/2017/02/170221222748.htm
https://en.wikipedia.org/wiki/William_Osler
https://agsjournals.onlinelibrary.wiley.com/doi/full/10.1111/jgs.12244