Great post and explanation!

However, I would like to discuss the last sentence. Wouldn't you agree that "Vomiting the microorganisms and their toxins is a protective mechanism that helps prevent the passage of theses substances to the small intestines...." is not necessarily a protective mechanism in animals but is, in reality, a mechanism evolved by microorganisms to facilitate their spread in the environment?

I would argue that animals evolved the vomiting reflex to deal with toxic and irritating chemicals found in plants and the environment in general. My evidence would be that the vomiting reflex is controlled by our own endogenous serotonin and 5HT-3 receptors. If we ingest an irritating chemical, the inflammatory response causes an acute release of serotonin in the gastro tract which can lead to activation of the 5HT-3 receptors and vomiting.

When it comes to microorganisms, some have evolved proteins over time that can also bind to and activate the 5HT-3 receptor directly.

However, I will concede that infection by microorganisms themselves can cause localized gastric irritation (by way of activation or our own immune system) which can lead to release of gastric serotonin. But, again, this inflammation is just a localized immune response....same thing that could happen with an irritating chemical from a plant.

In the case of vomiting directly from the toxins produced by microorganisms, I still say that is not a protective mechanism. The human body does not "know" it has been invaded by a toxin, so it therefore is not itself activating the vomiting reflex spontaneously because of the toxin. The toxin is literally binding to the receptor that activates the vomiting center.

I suppose it's a bit of which came first...the chicken or the egg.

For vomiting, yes. For diarrhea, ehhh not so much...but the jury is still out on that. It really depends what bacteria or virus has infected your gastro tract. With diarrhea, the main concern is the strain of E. coli that produces a toxin that can cause kidney damage if not treated...although this does not happen to everyone that is infected by that bacteria.

If you go to the ER for vomiting, chances are they will give you ondansetron (or a similar anti-emetic). In most people, this will stop the vomiting within 15 to 30 minutes and allow the person to drink fluids. Obviously, if it didn't stop, they would give you an IV.

The point here is that the toxins causing the sickness are unlikely to cause harm to your body if you block the 5HT-3 receptor they are binding to and activating. Vomiting as it relates to the gastro tract is controlled pretty much exclusively by serotonin and the 5HT-3 receptor.

For example, if you eat something and it irritates your stomach and small intestinal mucosa (not because of bacteria or viruses....think eating like a whole carolina reaper pepper or something similar that is irritating), certain immune cells will become activated by the inflammation and will release serotonin. That serotonin will then bind to and activate the 5HT-3 receptors which will directly stimulate the vomiting center in the brain. Obviously, the reason animals evolved this mechanisms was help expel noxious foods and make us adverse to them in the future.

Now, another example is food poisoning. There are many types, and I won't go into crazy detail. Let's consider the most common...Staph food poisoning. Certain strains of Staph that find their way into food (think somebody handling food with their bare hands) will grow and produce an emetic toxin (if the food is not stored properly). This toxin, if ingested, directly binds to and activates that 5HT-3 receptor...i.e. it directly activates the vomiting center in the brain. These bouts tend to be short in duration with no lasting effects. Therefore, taking a damn anti-emetic (like generic Zofran...ondansetron) is fine. All it does is bind to and inactivate the 5HT-3 receptor in the gut. It literally just blocks either serotonin or toxins from binding and activating the receptor.

So, the next time you are sick to your stomach and it is dragging on, call your doctor and ask for ondansetron. The huge benefit to this medication is that it normally works very well and will allow you to re-hydrate...and we all know that is the most critical part of gatro illnesses.

The human body cannot identify toxins i.e. the human body cannot think. The human body can only react to exogenous stimulus. It's such a common misconception that our bodies can actively find and know noxious stimuli. It's likely because growing up, we likely all had parents who told us vomiting or diarrhea was our body's way of getting rid of the bad stuff. However, that is just not the case...it's comforting to hear that as a child, but it's actually quite the opposite in reality. Reality is that bacteria and viruses have evolved proteins that bind to and activate certain receptors in our gastrointestinal tract and cause a multitude of different effects. For instance, in the majority of food poisoning cases, the toxin is likely an emetic toxin that literally binds to and activates the 5HT-3 receptor in the small intestine. This is a serotonin receptor that directly activates the vomiting center in the brain, so when you consume a food that has been improperly stored/contaminated by a bacterium that produces an emetic toxin, that toxin directly activates your vomiting center. These toxins and the genes that encode them have been highly conserved over time as they allow the bacteria that make them to spread rapidly through the environment. That's really all a bacteria or virus wants to do....multiply and spread...but please don't take that as me saying that bacteria and viruses are thinking. They are not...haha.