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Heartburn, Nausea, and Vomiting

For medical students2 min readUpdated 2026-10-10

Heartburn, nausea, and vomiting are critical pathophysiological phenomena reflecting motor dysfunction of the upper gastrointestinal tract. These processes can act either as evolutionary protective reflexes to clear the body or as severe pathological conditions leading to exhaustion.

Localization of heartburnThe burning sensation occurs strictly in the lower esophagus.
Nature of nauseaIt forms during subthreshold excitation of the vomiting center neurons.
Control centerThe vomiting center is anatomically located in the medulla oblongata.
Protective functionEmergency evacuation of toxic substances and foreign bodies from the stomach.

Heartburn and Gastroesophageal Reflux

Heartburn is traditionally described as a specific burning sensation localized in the lower esophagus. The pathophysiology of this symptom is based on impaired sphincter closure.

A key triggering factor is the pathological decrease in the tone of the cardiac sphincter of the stomach (also known as the lower esophageal sphincter). Normally, this sphincter prevents the backflow of food. However, when its tone drops, conditions are created for the development of gastroesophageal reflux. This process represents the uncontrolled backflow of acidic contents from the stomach cavity back into the esophageal lumen. It is the contact of the acidic environment with the mucous membrane that generates the characteristic burning sensation.

Nausea as a Precursor

In pathophysiology, nausea is defined as an extremely unpleasant yet completely painless subjective sensation. As a rule, this condition acts as a direct precursor to the upcoming act of vomiting.

From a neurophysiological standpoint, the mechanism of nausea is based on subthreshold excitation of the vomiting center neurons. This means that a stimulating signal is already entering the central nervous system, but its strength is not yet sufficient to cross the excitation threshold and trigger a full motor reflex.

Physiology and Mechanism of Vomiting

Vomiting is classified as a complex reflex involuntary act. Externally, it manifests as the forceful expulsion of the contents of the stomach (and in some cases, the intestine) outward. The ejection of masses occurs sequentially through the esophagus, pharyngeal structures, and oral cavity.

The central structure controlling this process is the activation of neurons in the vomiting center of the medulla oblongata. The physiology of the act itself is a strictly coordinated chain of combined phenomena:

  1. A sharp increase in antiperistalsis of the gastric wall ( contraction waves moving in the reverse direction).
  2. Simultaneous powerful contraction of the diaphragm muscles and abdominal wall musculature, creating high pressure.
  3. Obligatory relaxation of the muscles of the cardiac region of the stomach and esophagus to ensure the unobstructed exit of masses.

Pathogenic and Protective Significance of Vomiting

When assessing the significance of vomiting for the body, two diametrically opposed aspects are distinguished:

The clinical significance of these losses multiplies and becomes critical in prolonged and/or recurrent vomiting, requiring close medical attention.

Mnemonic

To remember the physiology of vomiting, use the three-step rule: "Antiperistalsis — Tension — Relaxation." First, the stomach pushes masses backward (antiperistalsis), then the diaphragm and abdominal wall squeeze from the outside (tension), and the cardia and esophagus open the pathway (relaxation).

Frequently asked questions

What factors and substances cause a pathological decrease in cardiac sphincter tone?

Pathological decrease in tone/dysfunction of the cardiac (lower esophageal) sphincter is associated with the following factors:

  • systemic diseases, primarily systemic sclerosis (atrophy of cardiac muscles);
  • acquired weakness of the lower esophageal sphincter;
  • pregnancy;
  • vagotomy;
  • peptic ulcer disease;
  • any mechanical disruption of the closing sphincter;
  • administration of drugs that reduce sphincter tone: anticholinergics, sedatives, hypnotics, beta-blockers, nitrates.
What receptor zones and afferent pathways stimulate the vomiting center?

Activation of the vomiting center in the medulla oblongata occurs through several stimulation pathways:

  • chemoreceptor trigger zone on the floor of the 4th ventricle — responds to chemical substances in the blood or CSF;
  • peripheral stimulation — receptors of the pharynx and gastric mucosa;
  • vestibular apparatus — during motion sickness ("motion sickness").

Receptor mapping by source: the trigger zone contains D2-dopamine and 5-HT3-serotonin receptors; vestibular nuclei contain M1-cholinergic and H1-histamine receptors; visceral afferent system from the pharynx and stomach utilizes 5-HT3 receptors.

What is the main cause of heartburn?

It is based on a decrease in the tone of the lower esophageal (cardiac) sphincter, which allows acidic gastric contents to reflux into the esophagus (gastroesophageal reflux).

How does nausea differ from vomiting in neurophysiology?

Nausea occurs with subthreshold excitation of the vomiting center. When the excitation reaches the threshold, the full reflex act of vomiting is triggered.

Which muscles provide the expulsion of contents during vomiting?

Expulsion occurs due to enhanced gastric antiperistalsis, as well as powerful simultaneous contractions of the abdominal wall muscles and diaphragm.

In what cases does vomiting become dangerous for the patient?

Vomiting acquires pronounced pathogenic significance when prolonged or recurrent, as it leads to critical loss of fluid, ions, and nutrients by the body.

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