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Addis Ababa University College of Health Sciences Department of Medical Physiology Presentation on Gastro intestinal Reflexes By Girmay fitiwi 06/11/2022 1

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Page 1: gastro intestinal reflexes

Addis Ababa UniversityCollege of Health Sciences

Department of Medical Physiology

Presentation on Gastro intestinal Reflexes

By Girmay fitiwi

04/12/2023 1

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Presentation out Line

1.Objectives 2.Introduction 3.Short reflexes 4. Long reflexes 4.1. Defecation reflexes 4.2. Vomition (emesis ) reflexes5. References

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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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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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…………..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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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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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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Different nervous reflexes of the GIT

04/12/2023 Fig.1 different gastro intestinal reflexes 8

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GI reflex Cont’d

Fig.2 reflex control of gut activity

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Gastric glands

Fig .3 Short reflex

Distension of stomach by food

Mucous membrane of stomach is stimulated

Afferents go to internal plexus

Efferents from internal plexus

Release of gastric juice

G- cells in pyloric glands

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Gastric glandsFig.4 Long reflex

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

Release of gastric juice

G-cells in pyloric glands

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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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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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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

From CNS

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1

2

3

Nerve impulsesinhibit peristalsisin stomach wall

Duodenumfills with chyme

Sensory stretchreceptors arestimulated

Sensory nerveimpulses travelto centralnervous system

To CNS

Vagusnerve

Fig.5 enterogastric reflexes

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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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……….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.

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………….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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…………..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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……………..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.

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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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Defecation reflexes cont’d

04/12/2023 21Fig 6. anatomical view of rectum and anal channel

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…………..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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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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04/12/2023Fig7. defecation reflexes

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…………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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………………….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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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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…………….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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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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…………cont’d

• Vomiting may be induced by:-1.Drugs like apomorphine stimulate CTZ.2.Afferent impulses from vestibular nuclei • They mediate vomiting of motion sickness3.Afferent impulses from viscera stimulate vomiting

center via NTS.• Vomiting induced in visceral disease.

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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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