Vomiting reflex

1. VOMITING REFLEX ( Emetic Reflex) CHHABI LAL MAHATARA(32) PUSPA PARAJULI(62) KATHMANDU UNIVERSITY DEPATMENT OF PHARMACY BATCH 2013(III Sem.) 12/8/2014 1

2. TERMINOLOGY Nausea - 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

3. VOMITING CENTER Vomiting center is situated bilaterally in medulla oblongata near the tractus solitarius The sensory impulses from the irrited part of GIT or other organs are transmitted to the vomiting center through vagus and sympathetic afferent fibers . The motor impulses causing act of the vomiting are transmitted from vomiting center through V, VII,IX, X and XII cranial nerves to the upper part of gastrointestinal tract and through spinal nerves to diaphragm and abdominal muscle .

4. MECHANISM OF VOMITING ( EMESIS ) Movements in the GIT start even before actual vomiting During 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.

5. 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.

6. During Ejection of Vomitus The esophagus is relaxed throughout. Glottis closed. Larynx and Hyoid bone drawn upward and forward. Respiration inhibited. Throat is diluted to allow free exit of vomitus. The entry of vomitus into Nasopharynx is prevented by the Elevation of Soft Palate .

7. VOMITING REFLEX (EMETIC REFLEX) There are three steps in the vomiting reflex First - N ausea 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.

8. NAUSEA An unpleasant sensation that immediately precedes vomiting Cold sweat, pallor, salivation Noticeable disinterest in the surrounding

9. W ithout any expulsion of gastric contents. Can occur without vomiting B ut normally it generates the pressure gradient that leads to vomiting.  Retching Follows Nausea

10. Vomiting Follows Retching

11. Vomiting reflex activity that is not under voluntary control.

12. The vomiting center receives input from four major areas 1) GI tract(Irritation of the mucosa of upper GIT is the strong stimulus for vomiting. Irritation of Duodenum provide the strongest stimulus ) 2) Chemoreceptor trigger zone 3) Vestibular apparatus 4) Higher Cerebral cortex .(SMELL,TASTE,PAIN,MEMORY, FEAR)

13. RECEPTOR IN VOMITING CENTER(MEDULLA) 1) Histamtne 2) Muscuranic 3) 5-HT

14. Chemoreceptor Trigger Zone It is the small area located bilaterally on the floor of 4 th 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.

15. Vestibular Apparatus Emesis due to Motion Sickness Rapidly changing direction of the motion of the body causes Vomiting This is because motion stimulates the labyrinth organs → abnormally stimulates a Vestibulocochler nerve(VIII)→Vestibular nucleus( HISTAMINE1,MUSCURINIC )→ Chemoreceptor trigger zone → Vomiting center → vomiting

16. EMESIS DUE TO CHEMOTHERAPY

17. CAUSES OF VOMITING

18. References   Gyton , H. (2006). Textbook of Medical Physiology. Krishna, A. ( 2014 ). Textbook of Medical Physiology. Deilhi : Dynamic Print Graffix .    

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