[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Physiology](https://durgical.com/en/physiology/) › [Gastrointestinal](https://durgical.com/en/physiology/#s-gi) › Vomiting and its control [Physiology](https://durgical.com/en/physiology/) · [Gastrointestinal](https://durgical.com/en/physiology/#s-gi) # Vomiting and its control - Regulation - Exam priority: medium Vomiting is a protective brainstem reflex that expels stomach contents; losing a lot of acid upsets the electrolytes. Updated 2026-11-01 Also called: Emesis, Chemoreceptor trigger zone **See it in 3D:** [Medulla oblongata](https://durgical.com/en/anatomy/medulla-oblongata/) · [Fourth ventricle](https://durgical.com/en/anatomy/fourth-ventricle/) · [Vagus nerve](https://durgical.com/en/anatomy/vagus-nerve/) · [Stomach](https://durgical.com/en/anatomy/stomach/) · [Diaphragm](https://durgical.com/en/anatomy/diaphragm/) · [Esophagus](https://durgical.com/en/anatomy/esophagus-abdominal-part/) ## Key points - Chemoreceptor trigger zone: area postrema, in the floor of the fourth ventricle, with no blood–brain barrier; it senses drugs and toxins in blood (D2, 5-HT3, NK1, opioid receptors). - Vagal route: serotonin from enterochromaffin cells (chemotherapy, radiation, infection) activates 5-HT3 receptors on vagal afferents. - Vestibular route (motion sickness): H1 and muscarinic receptors. - Sequence: nausea → deep breath → glottis closes and palate rises → diaphragm and abdominal wall contract while the esophageal sphincters relax. - HCl loss → metabolic alkalosis; hypovolemia activates aldosterone → renal K⁺ and H⁺ loss; urine Cl⁻ is low ( - A signal from the trigger zone, vagus, vestibule or cortex activates the vomiting generator in the medulla. - Nausea appears, with salivation, sweating, pallor and tachycardia (autonomic discharge). - A retrograde contraction carries small-bowel contents back into the stomach. - A deep breath is taken, the glottis closes and the soft palate seals the nasopharynx to protect the airway. - The diaphragm and abdominal muscles squeeze the stomach while the esophageal sphincters relax: contents are expelled. - Repeated loss of gastric juice leaves HCO₃⁻ unmatched (an un-neutralized alkaline tide) and contracts extracellular volume. ## Regulation - *+* **Chemoreceptor trigger zone (D2, 5-HT3, NK1)**: Opioids, digoxin, chemotherapy, uremia and toxins activate the vomiting centre - *+* **Vagal afferents (5-HT3)**: Gut irritation or distension and mucosal serotonin trigger the reflex - *+* **Vestibular system (H1, M1)**: Motion and Ménière disease - *+* **Cortex and limbic system**: Smells, sights, severe pain, anxiety, anticipatory nausea ## Clinical notes - Pyloric stenosis, high bowel obstruction or prolonged vomiting: metabolic alkalosis with hypochloremia and hypokalemia. - Bilious vomiting in a newborn: obstruction below the ampulla (malrotation with volvulus) until proven otherwise. - Vomiting with headache and papilledema: think of raised intracranial pressure, which stimulates the vomiting centre directly. - Antiemetics act on these receptors: D2, 5-HT3, NK1 and H1 antagonists and antimuscarinics. ## Memory aid 'Four doors to the vomiting centre': blood (trigger zone), gut (vagus), ear (vestibule) and mind (cortex). ## Test yourself Think of the answer, then tap the question to see it. ## Why can the chemoreceptor trigger zone detect drugs and toxins in the blood? It lies in the area postrema, in the floor of the fourth ventricle, one of the regions without a blood–brain barrier; its neurons are directly exposed to what circulates in plasma. ## Why does prolonged vomiting cause hypokalemia when gastric juice holds little potassium? Hypovolemia activates aldosterone, and excess filtered HCO₃⁻ carries Na⁺ to the distal tubule; both increase renal K⁺ secretion, which is the main loss. ## Which pathway explains the severe nausea caused by chemotherapy? Chemotherapy damages the mucosa and releases serotonin from enterochromaffin cells, which activates 5-HT3 receptors on vagal afferents and in the trigger zone. ## In metabolic alkalosis from vomiting, what urine chloride is expected and why? Low ( [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/physiology/vomiting-and-its-control/) ## See it in 3D The structures of Durgical's 3D anatomy where it happens. - [Medulla oblongata](https://durgical.com/en/anatomy/medulla-oblongata/) - [Fourth ventricle](https://durgical.com/en/anatomy/fourth-ventricle/) - [Vagus nerve](https://durgical.com/en/anatomy/vagus-nerve/) - [Stomach](https://durgical.com/en/anatomy/stomach/) - [Diaphragm](https://durgical.com/en/anatomy/diaphragm/) - [Esophagus](https://durgical.com/en/anatomy/esophagus-abdominal-part/) ## Related topics - [Metabolic alkalosis and its compensation](https://durgical.com/en/physiology/metabolic-alkalosis-and-its-compensation/) - [Gastric motility and emptying](https://durgical.com/en/physiology/gastric-motility-and-emptying/) - [Swallowing and esophageal motility](https://durgical.com/en/physiology/swallowing-and-esophageal-motility/) - [The vestibular system, tone and posture](https://durgical.com/en/physiology/the-vestibular-system-tone-and-posture/) - [CSF and the blood–brain barrier](https://durgical.com/en/physiology/csf-and-the-blood-brain-barrier/) - [Potassium balance](https://durgical.com/en/physiology/potassium-balance/) ## Related conditions - [Metabolic alkalosis](https://durgical.com/en/conditions/metabolic-alkalosis/) - [Hypokalaemia](https://durgical.com/en/conditions/hypokalaemia/) - [Infantile hypertrophic pyloric stenosis](https://durgical.com/en/conditions/infantile-hypertrophic-pyloric-stenosis/) - [Small bowel obstruction](https://durgical.com/en/conditions/small-bowel-obstruction/) - [Acute (viral) gastroenteritis](https://durgical.com/en/conditions/acute-gastroenteritis/) - [Ménière disease](https://durgical.com/en/conditions/meniere-disease/) ## In Pharmacology - [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/) - [Morphine](https://durgical.com/en/pharmacology/morphine/) - [Digoxin](https://durgical.com/en/pharmacology/digoxin/) [← All of physiology](https://durgical.com/en/physiology/) Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given. Sources: [23.4 The Stomach](https://openstax.org/books/anatomy-and-physiology-2e/pages/23-4-the-stomach) (OpenStax (Rice University), 2022); [Alkalosis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/001183.htm) (MedlinePlus, US National Library of Medicine, 2024); [Pyloric Stenosis](https://www.ncbi.nlm.nih.gov/books/NBK555931/) (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 67). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/physiology/vomiting-and-its-control/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/vomiting-and-its-control/