>>12708045T he gag reflex is a proximal way of trying to get the toxic substance out of the body. If the substance makes it far enough, m cells in the small intestine detect the impurity and through a series of reverse peristalsis ejects it through vomiting. Series of coordinated muscle contractions create pressure gradients to facilitate emission.
The "area postrema" is a brain area that scans the blood for toxins and evacuates the stomach contents. The stomachs own nervous system can initiate vomiting if it senses being overfilled. Interestingly, fear and anxiety can also elicit vomiting.
