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Vomiting: Mechanism, Causes and Consequences

Mechanism
Vomiting is the forcible expulsion of gastrointestinal contents through the esophagus and mouth. It results when receptors are stimulated which contribute impulses to the vomiting center in the brain. The vomiting center has inputs mainly from:

Stretch or irritant receptors in the stomach (responds to excessive gastric distention or ingestion irritants or emetics)
Chemoreceptor trigger zones in the floor of the fourth cerebral ventricle (responds to increases in ICP)
Mechanical receptors in the throat
Vestibular apparatus (responsible for the ‘travel/motion sickness’)

Sensory impulse stream from these receptors reach the vomiting center and initiate a number of motor responses. The diaphragm and the skeletal muscles of the abdominal wall contract to increase the intra-abdominal pressure. The cardiac sphincter relaxes and soft palate rise to close off the nasal passage (because the vomitus in highly irritant and must be prevented from coming into contact with the delicate nasal tissues). The stomach (or intestinal) contents are then forced upward through the esophagus, pharynx and out the mouth.

Causes

Gastrointestinal causes of vomiting include:

1.Obstructing disorders (bowel obstruction)

Pyloric, small bowel or colonic obstruction
Mechanical (tumor, hard feces, polyps, volvolus, complicated inguinal hernias)
Paralytic ileus (Hirschsprung disease)
Stricture (carcinoma, diverticular disease, Chron’s disease, ischemic colitis)

2.Enteric infection (viral, bacterial)
3.Impaired motor function

Gastropareisis

Intestinal pseudo obstruction

Functional dyspepsia

GERD

Consequences
Excessive or repeated vomiting can cause dehydration and may lead to severe disturbances in the electrolyte and acid-base balance in the body.
Dehydration – due to loss of water from the GI tract. Hypokalaemia – due to loss of the potassium ions in gastrointestinal secretions Hypochloremia – due to loss of chloride ions in the vomitus Alkalosis - due to loss of H+ ions in the vomitus. (Since large amount hydrochloric acid is lost in the vomitus, the blood becomes alkaline as the stomach attempts to replace its lost acid). These water and electrolyte disturbances must be considered when managing the patient.

dr.rufusrajadurai	Latest page update: made by dr.rufusrajadurai , Nov 28 2007, 12:19 PM EST (about this update About This Update Edited by dr.rufusrajadurai 2 words added 5 words deleted view changes - complete history)
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