What is the Physiology of Vomiting?

Patient Presentation
A 15-year-old male came to clinic with vomiting and diarrhea for 24 hours. The diarrhea was watery without mucous or blood and was already decreasing. The vomiting had occurred early in the illness and he had not had any for more than 12 hours. He was drinking and urinating well. The pertinent physical exam had normal vital signs and growth percentages were 10-25%. His examination showed moist mucus membranes and brisk capillary refill. His abdominal examination was negative.

The diagnosis of gastroenteritis was made. The patient and family were educated about signs of dehydration or increasing abdominal pain and fever. Afterwards, the medical student who had seen the patient had remarked about the very vivid description the boy had of his vomiting episodes and asked the attending to explain the physiology of vomiting. The attending said he remembered some general concepts that it was the abdominal musculature that was one of the real propulsive forces, plus the glottis closed off to protect the lungs. The medical student said he would look it up and talk with the attending again the next day.

Regurgitation is a passive expulsion of ingested material out of the mouth. It is a normal part of digestion for ruminants such as cows and camels. Nausea is an unpleasant abdominal perception that the person may describe as feeling ill to the stomach, or feeling like he/she is going to vomit. Anorexia is frequently observed. Nausea is usually associated with decreased stomach activity and motility in the small intestine. Parasympathetic activity may be increased causing pale skin, sweating, hypersalivation and possible vasovagal syndrome (hypotension and bradycardia). Retching or dry heaves is when there are spasmodic respiratory movements against a closed glottis. This often occurs just before emesis.

Differential diagnoses of different types of emesis can be found here.

Learning Point
Emesis, vomiting or vomition is when stomach (sometimes small intestine also) contents are propelled up the esophagus and out the mouth.
It is composed of three basic parts:

  • A deep breath is taken, the glottis closed to prevent aspiration into the lungs, while the larynx is raised which helps to open the upper esophageal sphincter. There is a decrease in respiration.
    The soft palate also closes to try to protect the posterior nares. The pylorus also contracts.

  • The diaphragm contracts downward sharply which creates negative thoracic pressures. This also assists the opening of the lower esophageal sphincter and the esophagus itself.
  • As the diaphragm contracts, the abdominal wall muscles vigorously contract which increases the intragastric pressure. As the pylorus is closed, the path of least resistance is through the relatively open esophagus.

Note the stomach’s fairly passive role in the process.

The area postrema lying inferior to the 4th ventricle in the medulla is the brain’s vomiting center. Neural structures in this area integrate information from the gastrointestinal tract and other organs (i.e. heart, bile ducts, peritoneum, etc.), other brain areas (i.e. vestibula) and direct chemoreception. This information is integrated and the decision to trigger or not trigger the process of emesis is made. Many antiemetic medications target the chemoreceptive area to help supress triggering the emesis process.

Questions for Further Discussion
1. List the complications of emesis?
2. What elements of the history and physical make the symptom of emesis more concerning for a higher risk etiology?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Nausea and Vomiting.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

Isselbacher KJ. Anorexia, Nausea and Vomiting in Harrison’s Principles of Internal Medicine. McGraw-Hill Book Company. New York, New York. 1987;174-175.

R. Bowen. Physiology of Vomiting.
Available from the Internet at http://www.vivo.colostate.edu/hbooks/pathphys/digestion/stomach/vomiting.html (rev. 4/10/96, cited 11/26/12).

ACGME Competencies Highlighted by Case

  • Patient Care
    1. When interacting with patients and their families, the health care professional communicates effectively and demonstrates caring and respectful behaviors.
    2. Essential and accurate information about the patients’ is gathered.
    3. Informed decisions about diagnostic and therapeutic interventions based on patient information and preferences, up-to-date scientific evidence, and clinical judgment is made.
    4. Patient management plans are developed and carried out.
    5. Patients and their families are counseled and educated.

  • Medical Knowledge
    10. An investigatory and analytic thinking approach to the clinical situation is demonstrated.
    11. Basic and clinically supportive sciences appropriate to their discipline are known and applied.

  • Practice Based Learning and Improvement
    16. Learning of students and other health care professionals is facilitated.


    Donna M. D’Alessandro, MD
    Professor of Pediatrics, University of Iowa Children’s Hospital