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VOMITING REFLEX(Emetic Reflex)
CHHABI LAL MAHATARA(32)PUSPA PARAJULI(62)
KATHMANDU UNIVERSITYDEPATMENT OF PHARMACY
BATCH 2013(III Sem.) 12/8/20141
TERMINOLOGYNausea-is an unpleasant subjective sensation that most
people have experienced at some point in their lives and usually recognize as a feeling of impending vomiting in the epigastrium or throat.
Retching-muscular activity of the abdomen and thorax, often
voluntary, leading to forced inspiration against a closed mouth and glottis without oral discharge of gastric contents.
Vomiting- Vomiting is a partially voluntary act of forcefully
expelling gastric or intestinal content through the mouth
VOMITING CENTERVomiting center is situated bilaterally in
medulla oblongata near the tractus solitariusThe sensory impulses from the irrited part of
GIT or other organs are transmitted to thevomiting center through vagus and sympatheticafferent fibers.
The motor impulses causing act of the vomitingare transmitted from vomiting center through V,VII,IX, X and XII cranial nerves to the upper partof gastrointestinal tract and through spinalnerves to diaphragm and abdominal muscle.
MECHANISM OF VOMITING (EMESIS)Movements in the GIT start even before actual vomitingDuring the excessive irritation of the stomach or upper part of intestine ,the antiperistalsis begins. And vomiting occurs few minutes after this.
The antiperistalsis in the ileum and runs backward through the intestine pushing the intestinal contents into duodenum and stomach within 3-5 minutes. The rate of antiperistalsis is about 2-3 cm per second.
After the antiperistalsis movements the voluntary muscle are put into action. At the same time,
there is relaxation of lower esophageal sphincter. After inspiratory movement, there is
closure of glottis. This is followed by contraction
of abdominal muscle with a characteristics jerk
called retching. This compress the stomach against contracted diaphragm and abdominal organs. And the pressure inside the stomach increased. This increased pressure causes
emptying of contents through the relaxed esophagus.
During Ejection of Vomitus1)The esophagus is relaxed throughout.2)Glottis closed.3)Larynx and Hyoid bone drawn upward and
forward.4)Respiration inhibited.5)Throat is diluted to allow free exit of
vomitus.The entry of vomitus into Nasopharynx is prevented by the Elevation of Soft Palate.
VOMITING REFLEX (EMETIC REFLEX)There are three steps in the vomiting reflex
First -Nausea develops.Second-retching occurs as a result of activation of spasmodic contractions of the diaphragm and intercostal muscles combined with closure of the glottis. Third- the act of vomiting occurs.
NAUSEAAn unpleasant sensation that immediately precedes vomiting Cold sweat, pallor, salivation Noticeable disinterest in the
surrounding
Without any expulsion of gastric
contents.
Can occur without vomiting
But normally it generates the
pressure gradient that leads to
vomiting.
RetchingFollows Nausea
VomitingFollows Retching
Vomiting reflex activity that is not under voluntary control.
The vomiting center receives input from four major areas 1) GI tract(Irritation of the mucosa of upperGIT is the strong stimulus for vomiting.Irritation of Duodenum provide the strongeststimulus )2) Chemoreceptor trigger zone3) Vestibular apparatus4) Higher Cerebral cortex.(SMELL,TASTE,PAIN,MEMORY, FEAR)
RECEPTOR IN VOMITING CENTER(MEDULLA)
1) Histamtne2) Muscuranic3) 5-HT
Chemoreceptor Trigger ZoneIt is the small area located bilaterally on the floor of 4th ventricle.A chemoreceptor(DOPAMINE 2, 5-HYDROXY TRYPTOMINE) cell initiate vomiting when they are electrically stimulated by certain circulating chemical agents.It is lies outside the blood brain barrier(BBB)Administration of certain crude drugs morphine, amorphine, digitalis derivative stimulate chemoreceptor zone and initiate vomiting.Destruction of this area inhibits vomiting but does not inhibit vomiting due to irrigative stimulation of upper GIT.
Vestibular ApparatusEmesis due to Motion SicknessRapidly changing direction of the motion
of the body causes VomitingThis is because motion stimulates the
labyrinth organs → abnormally stimulates a Vestibulocochler nerve(VIII)→Vestibular nucleus(HISTAMINE1,MUSCURINIC)→ Chemoreceptor trigger zone → Vomiting center → vomiting
EMESIS DUE TO CHEMOTHERAPY
CAUSES OF VOMITING
References
Gyton, H. (2006). Textbook of Medical Physiology.Krishna, A. (2014). Textbook of Medical Physiology. Deilhi: Dynamic Print Graffix.
ANYQUESTIONS???