1. Addis Ababa University
College of Health Sciences
Department of Medical Physiology
Presentation on Gastro intestinal Reflexes
By Girmay fitiwi
10/30/2011 1

2. Presentation out Line
1.Objectives
2.Introduction
3.Short reflexes
4. Long reflexes
4.1. Defecation reflexes
4.2. Vomition (emesis ) reflexes
5. References
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3. 1. Objectives
At the end of this presentation students willable to :-
• Mention the types of gastro intestinal reflexes
• Clarify the roles of different GI reflexes
• Explain the mechanisms of defecation reflexes
• list the control mechanisms of defecation
• Discuss the mechanism, merits and demerits of
vomiting reflexes.
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4. 2. introduction
• The digestive system has a complex system of
motility and secretion regulation which is vital for
proper function.
• Accomplished via a system of long reflexes from the
CNS, short reflexes from ENS and reflexes from GI
peptides working in harmony with each other.
• Three types of gastrointestinal reflexes .
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5. …………..cont’d
1.Local reflexes
• Reflexes that are integrated entirely within the gut
wall enteric nervous system.
• These include reflexes that control much
gastrointestinal secretion, peristalsis, mixing
contractions, local inhibitory effects.
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6. GI reflexes cont’d
2. Short reflexes
• Reflexes from the gut to the prevertebral sympathetic ganglia
and then back to the gastrointestinal tract.
• These reflexes transmit signals long distances to other areas
of the gastrointestinal tract.
• gastrocolic reflex
• enterogastric reflex.
• colonoileal reflex.
• Ileogastric reflex
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7. GI reflexes cont’d …………
3.Long reflexes
• Reflexes from the gut to the spinal cord or brain stem and
then back to the gastrointestinal tract.
 Vago vagal reflexes
 Pain reflexes that cause general inhibition of the entire
gastrointestinal tract.
 Defecation reflexes
 Vomition reflexes
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8. Different nervous reflexes of the GIT
10/30/2011 Fig.1 different gastro intestinal reflexes 8

9. GI reflex cont’d
10/30/2011 Fig.2 reflex control of gut activity 9

10. Distension of stomach by food
Mucous membrane of stomach is stimulated
Afferents go to internal plexus
Efferents from internal plexus
G- cells in pyloric
Gastric glands
glands
Release of gastric juice
10
Fig .3 Short reflex

11. Presence of food in stomach
Mucous membrane of stomach is stimulated
Afferents go via the vagus
Medullary centre
Efferents come via vagus
Synapse in the intrinsic plexuses
G-cells in pyloric
Gastric glands glands
Fig.4 Long reflex 11
Release of gastric juice

12. 3.Short Reflexes
1. Gastrocolic (Gastroileal) Reflex
• Stomach activity leads to ileocecal relaxation and
increased mass movements in the colon.
• These reflexes are mediated through both long and short
nervous pathways (extrinsic and intrinsic) and hormones
(CCK, gastrin)
 Most evident after first meal of the day.
 Often followed by urge to defecate.
 New born children routinely defecate after meal.
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13. Short reflexes cont’d
2.Enterogastric reflex
 When fat or protein chyme reaches the duodenum, receptors
detect and send impulses to enteric nerves of the stomach
that in turn cause the inhibition of stomacheal motility and
secretion.
 Delays emptying.
3. Intestino-intestinal
 Distention of one portion of the intestine leads to
decreased contractions caudad of the bolus.
 Depends on extrinsic neural connections.
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14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
4 Nerve impulses
inhibit peristalsis
in stomach wall
From CNS
Vagus
nerve
To CNS
1 Duodenum
fills with chyme
3 Sensory nerve
impulses travel
to central
2 Sensory stretch nervous system
receptors are
10/30/2011 Fig.5 enterogastric reflexes 14
stimulated

15. Short reflexes cont’d
4. Vago vagal reflexes
• GI reflex circuits where afferent and efferent fibers
of the vagus nerve coordinate responses to gut
stimuli via the dorsal vagal complex in the brain.
• Controls contraction of the GI muscle layers in
response to distension of the tract by food.
• Allows for the accommodation of large amounts of
food in the GITs.
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16. ……….cont’d
• Carries signals from stretch receptors,
osmoreceptors, and chemoreceptors to dorsal vagal
complex where the signal may be further transmitted
to autonomic centers in the medulla.
• Efferent fibers of the vagus then carry signals to the
gastrointestinal tract up to the splenic flexure.
10/30/2011 gastro intestinal reflexes 16

17. ………….cont’d
Function
• Active during the receptive relaxation of the
stomach in response to swallowing of food .
• When food enters the stomach a "vagovagal" reflex
goes from the stomach to the brain, and then back
again to the stomach causing a reduction in the
muscular tone of the stomach wall.
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18. …………..cont’d
Mechanism
• when the corpus and fundus of the stomach are
distended secondary to the entry of a food bolus.
• stimulation of the mechanical receptors located in
the gastric mucosa stimulates the vagus afferents.
• The completion of the reflex circuit by vagus
efferents leads to the stimulation of postganglionic
muscarinic nerves.
• These nerves release Ach to stimulate two end
effects.
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19. ……………..cont’d
1.The parietal cells in the body of the stomach are stimulated to
release H+.
2. The ECL cells of the lamina propria of the body of the stomach
are stimulated to release histamine.
10/30/2011 gastro intestinal reflexes 19

20. 4. Long reflexes
4.1 defecation reflexes
• An Intrinsic reflex mediated by the local enteric nervous
system in the rectal wall.
• To be effective it usually must be fortified by parasympathetic
defecation reflex
• Distention of the rectum causes the internal anal sphincter to
relax, which produces the urge to defecate.
• The external anal sphincter is under voluntary control.
• relaxation of this sphincter, coupled with contraction of the
rectum and sigmoid colon, results in defecation.
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21. Defecation reflexes cont’d
10/30/2011 Fig 6. anatomical view of rectum and anal channel 21

22. …………..cont’d
• Rectum usually (almost) empty (retrograde contractions return
content to sigmoideum, until there is too much of it)
• Just before defecation mass movement in sigmoideum fills
rectum pressure reflex relaxation of inner sphincter
(smooth muscle) & contraction of outer sph. (skeletal muscle
controlled intentionally via pudendal nerves)
• Stretch receptors in rectal wall can adapt - urge to defecate
can temporarily subsided suppressed.
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23. Defecation Reflexes cont’d
A. Intrinsic reflex
• Intrinsic reflex mediated entirely by ENS is initiated
when feces enters rectum via mass movements and
the rectal pressure increase to 55 mmHg.
– Peristaltic waves in descending colon, sigmoid and
rectum
– Relaxation of internal anal sphincter (inhibitory
action of the myenteric plexus)
– Weak when functioning alone.
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24. 10/30/2011 24
Fig7. defecation reflexes

25. …………cont’d
B.Parasympathetic defecation reflex
• Involves sacral segments of the spinal cord .
• Greatly intensifies intrinsic reflex (but is not different
qualitatively)
• Afferent signals go to sacral cord and then back to
descending and sigmoid colon, and rectum by way of
parasympathetic fibers in pelvic nerves.
• The lower neurons S2-S4 provide sensory and motor
fibers for defecation reflex.
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26. 10/30/2011 gastro intestinal reflexes 26

27. ………………….cont’d
• Afferent signals entering spinal cord initiate other
effects that require intact spinal cord.
 Deep breath, closure of glottis, and increased abdominal
pressure
 Relaxation and movement of pelvis floor downward
 All work to move fecal contents downward
• Spinal transection or injury can make defecation a
difficult process.
• Cord defecation reflex can be excited (either digitally or
with enema) ,Forcing fecal particles into the rectum to
cause new reflexes, Not as effective as the natural reflexes.
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28. Vomiting (emesis)
• The ejection of stomach contents through the mouth.
• preceded with nausea, sometimes anorexia, autonomic
reactions (salivation, sweating, cold skin,...)
• Vomiting center in medulla (next to cardiovascular &
respiratory centers).
• CTZ located in the root of 4 th ventricle.
• Protective reflex against toxicity; however, longer
vomiting can cause metabolic alkalosis & dehydration.
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29. …………….cont’d
 There is a neural
connection between
vomition center and
CTZ.
 CTZ causes central
vomition and is
stimulated by chemical
substances (e.g., drugs
like morphine's ,
pregnancy, alcohol,
movement etc.)
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30. Vomiting cont’d
• Reverse peristalsis from the middle of small intestine
to larynx .
• Strong contraction of abdominal muscles&diaphragm.
• Relaxation, then closure of pylorus, relaxation of LES
and finally UES (glottis closure, inhibition of breathing)
• Forced inspiration against closed glottis -
intrathoracic pressure, abdominal (diaphragm)
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31. …………cont’d
• Vomiting may be induced by:-
1.Drugs like apomorphine stimulate CTZ.
2.Afferent impulses from vestibular nuclei
• They mediate vomiting of motion sickness
3.Afferent impulses from viscera stimulate vomiting
center via NTS.
• Vomiting induced in visceral disease.
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32. 10/30/2011 gastro intestinal reflexes 32

33. References
• Berne and levy physiology, sixth edition Bruce
M.Koeppen, Bruce A. Stanton
• Guyton and Hall Textbook of Medical Physiology, 12th
Edition.
• Human physiology: The Basis of Medicine, 3rd Edition.
• Lecture note
• Institutional websites
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