alright, so check out this guy, he’s gotsome nice looking lungs here, and he’s a pretty normal human so every time he breathes,he pulls in some oxygen. that oxygen zooms down this big airway, called the trachea,and then splits down one of the these two branches, called bronchi, then splits somemore into the bronchioles, until it finally ends up in these little sacs called alveoli,which sorta look like little clumps of grapes, and these guys are nestled right up againstsome tiny tiny blood vessels, and at this point the oxygen’s like seeya later, anddiffuses right into the bloodstream. now obviously oxygen’s not the only thing you’re breathingin though, is it? you’re constantly breathing in a ton of other stuff, especially, whetheryou like it or not, things like microorganisms.
you’re usually pretty good at making surethese guys don’t stick around though and you use techniques as simple as coughing toget rid of them, or you let your immune system do the dirty work. if a particularly nastyorganism makes it in, or your defenses aren’t very good, they can start to multiply andinfect your lungs. when an organism has successfully made your lungs their new home, like yourbronchioles or alveoli, you’ve developed something called pneumonia, which is thisinfection of your lungs. when these guys really get to multiplying, your immune system respondsby sending troops to help fight em off right? so things like white blood cells. these aregreat and all, because they’re trying to help, but what ends up happening is they causeinflammation in these areas where the organisms
have set up camp, so they fill with whiteblood cells and other things, like proteins, fluid, and even red blood cells. these obviouslytake up valuable space in your airways, right? so now this alveoli might be inflammed andfilled with fluid, so when you breath in some oxygen and it gets to these infected and inflammedairways, it’s gonna have a way harder time diffusing into the blood stream. so becauseyou aren’t getting that oxygen into your blood as easily, one common symptom is thislike shortness of breath and this difficulty breathing, which is also called dyspnea. also,like i mentioned, we cough to try and get things out of our lungs, so what do you thinkhappens when we’ve got all this fluid and other things built up? well we’re gonnatry to cough it up and make some room for
oxygen, so another big symptom is coughing.also, sometimes patients experience chest pains, why might that be? well there are definitelysome pain receptors near these airways and alveoli, so when they get inflamed, we cantotally feel that! and finally, since your immune system’s working to fight againstsome microbe, it’s also common to get a fever. ok ok, so notice that i’ve been prettygeneral about the culprit, this mysterious microorganism, why so vague? well, becausethere isn’t just one kind of microbe that causes pnemonia, it can actually be causedby all sorts of microbes. the most common ones though are bacteria and viruses, butit can also extend to fungi as well and something called mycoplasma. between viruses and bacteria,though, bacteria wins out and is the most
common cause of pneumonia in adults, especiallyone called streptococcus pneumoniaie, also sometimes known as pneumococcus, but justremember, it doesn’t necessarily have to be caused by this one bacterium, other bacteriathat may cause pnemonia are ones like haemophilus influenzae, legionella pneumophila, and staphylococcusaureus. aside from bacteria, viruses can also be a bigtime contributor to pneumonia cases,influenza probably being the most common virus that causes it, but it could also be causedby others. fungi rarely cause pnemonia because most of our immune systems fight them off...butfor people with weakened immune systems, like with aids or cancer, pneumonia from fungican become more of an issue. a common fungal culprit is pneumocystis jiroveci. finally,these things called mycoplasma can also cause
pneumonia in some cases. mycoplasma are technicallystill bacteria, one important point is that they don’t have a cell wall, so common antibioticslike penicillin that work by attacking cell walls, don’t work against these guys! luckilythough, they’re the smallest proportion that affects humans, and often don’t causeserious complications and can clear up on their own. so we know that pneumonia is this infectionof the lung tissue, and usually that infection’s caused by some bacteria or virus, but sometimesit’s fungal or caused by mycoplasma. at this point the microbe’s already in thelungs, but how does it get there? well just like there being a ton of microbes that causeinfection and pneumonia, there’s also a
ton of ways to actually contract these microbes,and we can categorize these. k so the first category of pneumonia, andalso the most common, is called community acquired pneumonia, sometimes just shortenedto cap. we can say that the pneumonia is community acquired when it happens outside of a hospitalor other healthcare setting. usually somebody gets this by breathing in microbes that livein your mouth, nose, or throat, and this one most often happens in the winter when yourimmune system is weaker. but, now guess what we call it when you getpneumonia from a healthcare setting or hospital, yep, we call those healthcare-associated pneumoniaand hospital-acquired pneumonia, respectively. what’s the difference though? well casesof hospital-acquired pneumonia, or nosocomial
pneumonia, include those where patients werealready hospitalized for something else, and healthcare associated pneumonia just refersto those that are in frequent contact with a healthcare setting, but aren’t necessarilyhospitalized, so that could be like nursing homes or long-term care facilities. thesetwo types tend to be more serious than community acquired pneumonia for a couple reasons. onereason is that the patients often have weakened immune systems already, like for hospital-acquired,they’re there because they’re already sick right? now throw a lung infection inthere, you can imagine how that might make things a little more complicated. the secondreason is that the microbes in hospitals are usually a more intense than in the ones floatinaround in the community. why’s that? well,
although hospitals do a great job at treatingand killing most bad microbes with antibiotics and other medicines, they also sometimes inadvertentlybecome these like breeding grounds for microbes that’re actually resistant to antibiotics,like methicillin-resistant staphylococcus aureus, which maybe you recognize as mrsa.normal staph can certainly cause pneumonia and other infections, but you can also killnormal staph using traditional antibiotics like penicillins. mrsa on the other hand,is like this mutant super staph that isn’t affected by normal antibiotics, making ita lot harder to treat. another important and more serious type of bacteria is pseudomonasaeruginosa, which also tends to be more resistant to traditional antibiotics. alright and oneother type that’s worth mentioning and is
along the same lines is called ventilatorassociated pneumonia. sick patients often need help breathing, so they’ll be connectedto a ventilator. if microbes somehow get in through the tube, they’ll be sucked intothe lungs, which can cause infection and pneumonia, especially for these patients that’re alreadyweak or sick. alright, so besides breathing in some invisiblemicrobe that you can’t even see, are there any other ways to get pneumonia? well, considerthis: you’re eating some french fries, instead of swallowing one, you accidentally breathit in, informally we call that going down the wrong pipe right? also though, we couldsay that you aspirated that french fry. ok now what happens? well normally you’d automaticallygag and start coughing and it’d go flying
across the room, maybe not, but it wouldn’tstay in there. what if these gag reflexes were compromised though? meaning that theyjust don’t work like they should, which is actually sometimes the case for patientswith brain injury or swallowing issues, or even those that’ve abused drugs or alcohol.so bits of it might stick around in your lower airways...and you could imagine that thatfrench fry probably isn’t the most sterile thing in the world, so it could be carryingsome potentially infectious microbes. if that microbe now infects the lungs and you getpneumonia, we would call this french fry pneumonia, just kidding, it’d be called aspirationpneumonia. and it doesn’t have to just be bits of food though, it could also be drinksor other materials, or even gastric contents,
like things from your stomach that’ve comeup one tube then gone back down the other tube instead. which can actually be prettynasty; because what does your stomach have in it? stomach or gastric acid. now thinkabout what might happen if that acid makes it into your lungs? nothing good, right? nopedefinitely not. if you aspirate some of those gastric contents into your airways you canget a chemical burn, which will initiate your body’s inflammatory reaction in your lungs. finally, a quick an easy type of pneumoniais called atypical pneumonia. atypical pneumonia basically just means that it was caused byone of these organisms: chlamydophila pneumoniae, legionella pneumophila, or mycoplasma pneumoniae.this type tends to be less serious than typical
pneumonia, and for that reason is sometimesreferred to as “walking pneumoniaâ€, because sometimes people just go about their dailylives with it. alright so by now we know there’s a tonof ways to classify pneumonia…and actually, that list keeps going! so another way thatwe can define a case of pneumonia is by where the infection is. when the infection is superpatchy, and maybe it’s only affecting these like scattered alveoli, we call that bronchopneumonia,which is defined by these scattered or patchy areas of consolidation. consolidation justmeans the tissue has filled with fluid and has gotten all hard and swollen. these areasalso usually have little tiny pockets of pus or white blood cells, also known as microabscesses,since they’re so small you can only see
them under microscope. along with being invarious areas of one side, they can also be bilateral, or on both sides. usually it happensthough in the lower lobes or the right middle lobe. speaking of lobes though, another waythough pneumonia can present itself is called lobar pneumonia. where bronchopneumonia wasall patchy and scattered, lobar pneumonia is this almost complete consolidation of awhole lobe of the lung. pretty much all cases, around 95%, of this are caused by the bacteriastreptococcus pneumoniae. usually lobar pneumonia happens in steps or stages, though. the firststage is called congestion, and lasts between 1 and 2 days, this is where the vessels startfilling with fluid. the next stage is called red hepatization, between day 3 and 4, thelobe starts to get reddish brown and firm,
and starts to resemble liver tissue, whichis why we call it hepat-ization. it’s color is red because it’s a combination of redblood cells, neutrophils and fibrin, which we can call an exudate, and this now becomesmore solid because this exudate is filling the air spaces. as the red blood cells breakdown and degrade, we move into stage 3 around days 5 to 7, called the gray hepatizationstage, where it’s still firm but the color has changed because the cells begin to breakdown. finally, the last stage is called resolution, and this happens around day 8 and can continuefor 3 weeks. in this stage the exudate gets digested by enzymes and broken up, ingestedby macrophages, or coughed up. and those are major pieces of lobar pneumonia, but there’sstill one more, someone could have interstitial
pneumonia, which is also just known as atypicalpneumonia which remember is this like walking pneumonia, and this type’s localized tothe tissue around alveoli, and usually there actually isn’t any exudate or fluid in thealveolar spaces, and so essentially no consolidation, but there will be some mononuclear infiltrate,like white blood cells that’ve infiltrated these interstitial spaces. this one, remember,is more rare and symptoms are typically pretty mild, like low fever and not a lot of mucus,similar to the flu. since there’s not a ton of mucus, usually patients will have anonproductive cough along with chest pains. usually, in order to figure out how the pneumoniais characterized as bronchopneumonia, lobar pneumonia, or interstitial pneumonia, we’dtake a chest radiograph, and this is pretty
much the gold standard. here’s an x-rayof someone with lobar pneumonia, see how the fluid’s localized to the upper right lobe?here’s one of bronchopneumonia, notice how the infected areas are spread out insteadof being localized to a single lobe. and finally here’s one of atypical or interstitial pneumonia,where you can see that the affected areas are more reticular because it’s affectingthe tissue outside the alveoli. another way one might be able to discern lobar pneumonia,where consolidation is a key factor, is by listening to various signs. for example, adullness to percussion is often a sign of consolidation. also though, you might be ableto feel more vibrations from the patient’s chest or back after they repeat certain phrases,a procedure called tactile vocal fremitus.
this is because the sound waves travel betterthrough the fluid-filled or consolidated tissue. late inspiratory crackles may also be heard,along with bronchial breath sounds, bronchophony and egophony. finally, you might also uselaboratory findings to figure out if pneumonia is present. the most useful lab finding isa positive gram stain, which is more useful than blood cultures, even though culturesare still used and you might look for neutrophilic leukocytosis, or an abnormally high levelof white blood cells in the blood, showing that the body is likely fighting off infectionof some kind.
