system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 how does nausea work? Does the level or degree to which you feel nauseous have anything to do with surface area of your stomach? Or what mechanism determines how nauseous you feel in a given situation?
gpt
Nurse here. Part of our brain (known as the medulla oblongata) senses substances (or chemicals) that tell our bodies they are sick or under extreme stress. When these substances are detected it triggers a warning to stop whatever you’re doing eating, spinning around fast, etc. That warning is nausea. There is a second part in the same area of the brain that gets triggered and causes the muscles involved in puking to contract and cause you to vomit. Vomiting is the body’s way of expelling something potentially harmful from inside you. 

Vomiting can have lots of triggers including illness, driving in a car, slow movement of food through your stomach/intestines, certain smells, hormones, exercise, anxiety, drugs, etc. 

Some people’s systems are more sensitive than others simply just because we are all unique individuals. Also, since the brain is part of your nervous system having an overreactive nervous system or certain medical conditions can make you more prone to nausea/vomiting.