I’ve been devoting three and a half loooong days to Anaesthesiology. It’s the big exam tomorrow. You might recall that I struggled a lot with this subject at the time of the class test. Well, I ended up doing pretty alright in that one. So the pressure is ON. As is my habit, I’ve managed to extrapolate some interesting (but less useful) knowledge from between the lines.
One of the chapters in our textbook is about post-operative nausea and vomiting. Now the thing that has always intrigued me most about nausea is that I get nauseous when I’m hungry. It baffles the mind because, from a survivalist point of view, the body would elicit a sensation that encourage finding sustenance – which, frankly, nausea just doesn’t do.
I tried Googling why this happens months and months ago, but didn’t really get a result other than “your tummy contracts because it’s hungry.” Yeah.
But (I think) I found an answer y’all!
So, basics: The vomiting centre is in your brain, and it has two main detectors, namely the GIT and the chemoreceptor trigger-zone (CTZ). Any emetogenic stimuli detected in the GIT will be transmitted via the Vagus nerve. The vagus nerve has two receptors, namely mechanoreceptors and chemoreceptors.
So, mechanoreceptors in the muscular walls of the GIT are activated by contraction of the GIT-muscles. Hungry tummy = contraction. So this is the first emetogenic stimulus.
The chemoreceptors involved are sensitive to noxious stimuli, as well as to certain endogenous chemicals like serotonin (5-Hydroxy-Tryptamine), histamine and dopamine. Now I’m not very up-to-date with all the GIT-physiology, but serotonin and dopamine especially play quite a big role in eating and anticipation of eating. In fact, dopamine is released to stimulate the appetite… and it so happens to be emetogenic.
Interestingly, when food is “off”, the gut will secrete more serotonin in order to increase gut motility (i.e. diarrhoea and nausea), so that the bad food gets out of the body more easily.
As always, I stand under correction, and this probably barely scrapes the surface of exactly how things work. I still thought it was pretty cool though. Except, they won’t ask this in the exam tomorrow.
Textbook: Principles of Anaesthesia for the Undergraduate Student, SUN PReSS, A. Coetzee