Vomiting: Causes and Mechanism

• Also called emesis.
• Abnormal emptying of stomach and upper part of intestine.
• Occurs through esophagus and mouth.

Causes

• Irritating contents in gastrointestinal tract.
• Pharynx stimulation mechanically.
• In case of pregnancy.
• Excess alcohol consumption.
• Consumption of drugs like antibiotics, opitaes, etc.
• Some kind of gastrointestinal disorder.
• Urinary tract infection, influenza which are of acute type.
• Sensory receptors abnormal stimulation in other organs like kidney, heart, etc.
• Labyrinthine apparatus unusual stimulation as in sea sickness, air sickness, swinging, etc.
• Nauseating sight, taste or odour.
• Metabolic disturbances (carbohydrate starvation and ketosis (pregnancy), uremia, ketoacidosis and hyper-calcemia).

 Image source: researchgate

Mechanism of Vomiting

Nausea

• Always initiated or preceded by nausea.
• Desire for vomiting is induced by nausea as it is unpleasant sensation.
• Secretion of large amount of saliva that contains more amount of mucus.

Retching

• It is a strong involuntary movement of GI tract.
• It starts even before actual vomiting.
• Intensification of feeling of vomiting occurs by these movements.
• This condition is called retching (try to vomit) which leads to vomiting after sometime.

Act of vomiting

• Series of movements are involved in vomiting.
• These movements occur in GI tract.

Events involved in vomiting

1.Beginning of antiperistalsis

• Runs from ileum towards the mouth through the intestine.
• Intestinal contents are pushed into the stomach afterwards.
• Velocity of the antiperistalsis is 2 to 3 cm/sec.

2. Temporary cessation of breathing after deep inspiration.

3. Closure of glottis.

4. Larynx and hyoid bone upward and forward movement.

5. Soft palate elevation.

6. Elevation of intra-abdominal pressure that results by the contraction of diaphragm and abdominal muscles initiated with a jerk.

7. Rise in intra-gastric pressure by the compression of stomach between diaphragm and abdominal wall.

8. Lower esophageal sphincter, esophagus and upper esophageal sphincter relax simultaneously.

9. Gastric contents (vomitus) expulsed forcefully through esophagus, pharynx and mouth.

10. The movements during act of vomiting throws vomitus to the exterior through above mentioned route.

Some movements are vital as the vomitus entry to other routes is prevented. This prevents the adverse effect of vomitus to many structures.

Movements that block vomitus to enter other routes

• Closure of glottis and cessation of breathing

*It blocks the vomitus to enter lungs.

• Elevation of soft palate

*It blocks the entry of vomitus to naso-pharynx.

• Upward and forward movement of larynx and hyoid bone

*It places them rigidly in their position which dilates the throat.

*Thus, vomitus gets free exit to come out.

  Image source: sciencedirect

Vomiting Reflex

• Vomiting is a reflex act.
• Irritated or distended part of GI tract or other organs develop sensory impulses.
• This impulse transmits to the vomiting center.
• Vagus and sympathetic afferent fibers are responsible for it.
• Vomiting center lies bilaterally in medulla oblongata near the nucleus tractus solitarius.
• Motor impulses are carried by V, VII, IX, X and XII ^th cranial nerves.
• These nerves arise from vomiting center and come to upper part of GI tract.
• Spinal nerves also carry these motor impulses to diaphragm and abdominal muscles.

References:

i) https://healthinfo.healthengine.com.au/nausea-and-vomiting-emesis#:~:text=The%20vomiting%20centre%20is%20predominantly,zone%20(CTZ)%20sending%20impulses.

ii) https://www.cambridge.org/core/books/abs/postoperative-nausea-and-vomiting/mechanisms-of-nausea-and-vomiting/F82278605852D316D86FBD271904D783

iii) https://www.frontiersin.org/about/about-frontiers

Vomiting: Causes and Mechanism