VOMITING

VOMITING

Vomiting or emesis is the abnormal emptying of stomach and upper part of intestine through esophagus and mouth.

CAUSES OF VOMITING

1. Presence of irritating contents in GI tract

2. Mechanical stimulation of pharynx

3. Pregnancy

4. Excess intake of alcohol

5. Nauseating sight, odor or taste

6. Unusual stimulation of labyrinthine apparatus, as in the case of sea sickness, air sickness, car sickness

or swinging

7. Abnormal stimulation of sensory receptors in other organs like kidney, heart, semicircular canals or

uterus

8. Drugs like antibiotics, opiates, etc.

9. Any GI disorder

10. Acute infection like urinary tract infection, influenza, etc.

11. Metabolic disturbances like carbohydrate starvation and ketosis (pregnancy), uremia, ketoacidosis

(diabetes) and hypercalcemia.

MECHANISM OF VOMITING

Nausea

Vomiting is always preceded by nausea. Nausea is unpleasant sensation which induces the desire for

vomiting. It is characterized by secretion of large amount of saliva containing more amount of mucus.

Retching

Strong involuntary movements in the GI tract which start even before actual vomiting. These movements

intensify the feeling of vomiting. This condition is called retching (try to vomit) and vomiting occurs few minutes after this.

Act of Vomiting

Act of vomiting involves series of movements that takes place in GI tract.

Sequence of events:

1. Beginning of antiperistalsis, which runs from ileum towards the mouth through the intestine, pushing

the intestinal contents into the stomach within few minutes. Velocity of the antiperistalsis is about 2 to

3 cm/second

2. Deep inspiration followed by temporary cessation of breathing

3. Closure of glottis

4. Upward and forward movement of larynx and hyoid bone

5. Elevation of soft palate

6. Contraction of diaphragm and abdominal muscles with a characteristic jerk, resulting in elevation of

intra-abdominal pressure

7. Compression of the stomach between diaphragm and abdominal wall leading to rise in intragastric

pressure

8. Simultaneous relaxation of lower esophageal sphincter, esophagus and upper esophageal sphincter

9. Forceful expulsion of gastric contents (vomitus) through esophagus, pharynx and mouth.

Movements during act of vomiting throw the vomitus (materials ejected during vomiting) to the exterior

through mouth. Some of the movements play important roles by preventing the entry of vomitus through other routes and thereby prevent the adverse effect of the vomitus on many structures.

Such movements are:

1. Closure of glottis and cessation of breathing prevents entry of vomitus into the lungs

2. Elevation of soft palate prevents entry of vomitus into the nasopharynx

3. Larynx and hyoid bone move upward and forward and are placed in this position rigidly. This causes

the dilatation of throat, which allows free exit of vomitus.

VOMITING REFLEX

Vomiting is a reflex act. Sensory impulses for vomiting arise from the irritated or distended part of GI tract or other organs and are transmitted to the vomiting center through vagus and sympathetic afferent fibers.

Vomiting center is situated bilaterally in medulla oblongata near the nucleus tractus solitarius. Motor impulses from the vomiting center are transmitted through V, VII, IX, X and XII cranial nerves

to the upper part of GI tract; and through spinal nerves to diaphragm and abdominal muscles.

Center for Vomiting during Motion Sickness and Vomiting Induced by Drugs

Center for vomiting during motion sickness and vomiting induced by drugs such as morphine, apomorphine, etc. is on the floor of fourth ventricle. This area is called chemoreceptor trigger zone. During motion sickness, the afferent impulses from vestibular apparatus reach vomiting center through this zone.

Center for Psychic-stimuli-induced Vomiting

Center for vomiting due to psychic stimuli such as nauseating odor, sight or noise is in cerebral cortex.

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