I learned this today. There is a carefully choreographed sequence of steps that enable us to vomit.
Vomiting is a form of protection. It is the body’s way of getting rid of threats or things it feels might be dangerous. This could be a poison, it could be a chemical, it could be a virus or a bacteria. The body’s first line of defense is to get the dangerous thing out before it can go further into the body and cause more damage.
Not all living creatures can vomit. Rodents aren’t able to vomit, which is why rat poison works. Most mammals will vomit after ingesting poison, but rats can’t, so the rat poison gets digested and kills them. The reason they can’t is to do with their brains, the way their stomachs have evolved, and the strength of their diaphragms.
So, how do we vomit? The first step is the signal that starts the vomiting process. There are different processes that send this signal depending on what has been affected. Motion sickness, for example, starts with a signal sent from the inner ear because it confuses the dizziness with being poisoned. Stomach infections or ingesting poisons starts with signals from our stomachs and intestines that are sent from special sensor cells that use serotonin. These cells are triggered by chemical, viral or bacterial sources and they send a signal up the vagus nerve to the brain. Being drunk starts with a signal from the liver because alcohol levels are too high to break down and it needs to expel it from the body.
The signals all converge on the chemoreceptor trigger zone (CTZ), which is at the base of the brain, just to the back of the brain stem, in a place called the fourth ventricle. The CTZ can be triggered by different signals and it decides what reaction each one needs. If it decides that vomiting is called for, the CTZ initiates the next steps in the process.
The next step is increased salivation. Your saliva glands go into overdrive and your mouth starts to water a lot. This is because the contents of your stomach are very acidic and the enamel on your teeth can be eaten away and damaged by acid. The increased saliva will wash the acid off your teeth before it can do any damage.
Simultaneously, you start to breathe more deeply. This is to oxygenate your blood because you will involuntarily hold your breath the moment before you vomit. Your body does this so that none of the vomit will go down your windpipe into your lungs and choke you.
Your small intestine starts to reverse itself. Food is carried along the small intestine by a process called peristalsis. This is where the muscles alternately contract and relax to move food along. Before vomiting, this process reverses and the muscles start to move food backwards. This is why your stomach feels peculiar before vomiting.
The sphincter muscle at the bottom end of the stomach relaxes so that the contents of the small intestine can come back up.
The diaphragm contracts in short pulses to raise the pressure within the abdomen and lower the pressure in the chest. The abdominal muscles contract for long periods of time raising the pressure even more. When the pressure is as high as it can get, the sphincter on the top end of the stomach relaxes and the pressure difference forces the contents of the stomach back up the throat and out of the mouth.
After you have vomited, the body does three things to help you. Firstly, the sympathetic nervous system raises your heart rate to get more blood to the muscles that you have been using. Vomiting can cause a lot of exertion. Secondly, it starts to make us sweat to reduce the heat that we gained by using our stomach muscles so much. And, thirdly, endorphins are released in the brain to make us feel better and to reduce the pain.
If the item or the problem has been removed from the body, vomiting ceases. If it is still there, the process repeats.
So, our body has an incredible way of getting dangerous things out of our bodies. It protects our teeth, protects our lungs, expels the contents of the stomach using a pressure difference, makes us sweat to cool down, and then release endorphins so we don’t feel so bad. A pretty impressive system. I’m going to try to remember this the next time I am sick. And this is what I learned today.
Photo by Engin Akyurt: https://www.pexels.com/photo/a-rustic-comfort-room-3620234/
Sources:
https://en.wikipedia.org/wiki/Vomiting
https://www.columbiatribune.com/story/lifestyle/family/2017/08/01/thrown-up-science/985640007/
https://www.gohealthuc.com/library/vomiting-causes
https://www.sciencefocus.com/the-human-body/what-happens-in-my-body-when-i-vomit/
http://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/vomiting.html
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8198651/
https://www.news-medical.net/health/Vomiting-Mechanism.aspx