Physiology of Vomiting

Vomiting is forceful expulsion contents of the stomach and upper small intestine through the mouth. In vomiting gut motility is centrally regulated. Emesis is medical term for vomiting.

There are three types of causes for vomiting.

1.    Neural

2.    Psychic

3.    Chemical causes

Reflex of vomiting mediated by the vomiting center of medulla. So, involve somatic nervous system and autonomic nervous system. Vomiting is frequently preceded by profuse salivation, sweating, elevated heart rate and the sensation of nausea. (nausea is the feeling of vomiting but contents are not expelled through mouth). Vomiting is not due to contraction of stomach. In vomiting stomach, esophagus and sphincters are relaxed. The role of the stomach is passive.

 

                        Physical, neural and chemical causes

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                        Impulses from vomiting center

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Contraction of diaphragm and abdominal muscles compresses small intestine and stomach

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Contents of intestine enter to the stomach by reverse peristalsis

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Ejection of gastric contents to esophagus

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Relaxation of lower esophageal sphincter and content enter to the esophagus

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Relaxation of upper esophageal sphincter

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Closure of glottis and raising of soft pallet

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Inhibition of respiration. Breath is held in mid inspiration

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Expelling the contents through mouth forcefully

 

 

Triggers for vomiting

Neural causes

 irritation of an organ, inflection of inflammation can produce vomiting. In gastrointestinal tract, peptic ulcer, gastritis, pancreatitis, hepatitis are caused for vomiting. In outside of the gastrointestinal tract, bacterial and viral infections increased intercranial pressure.

 

Chemical causes

Diabetic ketoacidosis (ketone bodies), kidney failure, liver failure, bacteria/viral infections, some drugs such as, Morphine, pethidine, chemotherapy. Chemicals do not directly act on vomiting center. Chemicals act through chemoreceptors trigger zone (CTZ) in area postrema. chemoreceptor trigger zone is not covered by blood brain barrier. Thus, substances can directly can act on chemoreceptor trigger zone. From chemoreceptor trigger zone impulses will reach the vomiting center. Or else chemoreceptor trigger zone impulses reach the vomiting center via NTS.

Vomiting in pregnancy is morning sickness. High circulating levels of HCG will act on chemoreceptors trigger zone and then vomiting zone is stimulated.

 

Psychic causes

Disgusting smell sights, anxiety, extreme pain myocardial infraction, ureteric colic, intestinal colic. These causes will reach the vomiting center via high center.

 

Motion sickness

Labyrinth of ear

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Vestibular nuclei

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Cerebellum

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Vomiting center

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Major consequences of severe vomiting

              

Loos isotonic gastric juice

Dehydration

Alkalosis

Hypokalemia

Hypochloremia

 

Principles of management

Treatment of the cause of vomiting

Replenish the fluid and electrolyte loss

ORS (oral rehydration solution) -if it is a mined one ECF volume is increased

Normal saline – if it is a severe vomiting, ECF volume is increased

Antiemetics – to stop vomiting

 

Many antiemetics prevent vomiting by inhibiting chemoreceptor trigger zone.