Question: when we are ill, what makes us be sick (literally sick)?

Sarah Harris answered on 20 Nov 2014:

Hi Flori,

After you’ve eaten dodgy food or have a virus, toxins trigger receptors in the vomiting centre of your brain (or “area postrema”). These receptors cause a signalling cascade that leads to your abdominal muscles contracting and glottis (your voice box) relaxing. The abs contracting and relaxed glottis force your stomach contents upwards and out through your mouth.

Some drugs also have vomiting as a side effect – that’s because there’s no blood-brain barrier across the vomiting centre, so the drugs can pass through and activate the receptors there. Anti-sickness drugs have the opposite effect, so they block signalling by the receptors in the vomiting centre and stop you getting sick!