gastro intestinal reflexes
Post on 25-May-2015
17.396 Views
Preview:
TRANSCRIPT
Addis Ababa UniversityCollege of Health Sciences
Department of Medical Physiology
Presentation on Gastro intestinal Reflexes
By Girmay fitiwi
04/12/2023 1
04/12/2023
Presentation out Line
1.Objectives 2.Introduction 3.Short reflexes 4. Long reflexes 4.1. Defecation reflexes 4.2. Vomition (emesis ) reflexes5. References
2gastro intestinal reflexes
04/12/2023
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.
3gastro intestinal reflexes
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 .
04/12/2023 gastro intestinal reflexes 4
…………..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.
04/12/2023 gastro intestinal reflexes 5
04/12/2023
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
gastro intestinal reflexes 6
04/12/2023
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
gastro intestinal reflexes 7
Different nervous reflexes of the GIT
04/12/2023 Fig.1 different gastro intestinal reflexes 8
04/12/2023 9
GI reflex Cont’d
Fig.2 reflex control of gut activity
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
10
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
11
04/12/2023
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.
gastro intestinal reflexes 12
04/12/2023
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.
gastro intestinal reflexes 13
04/12/2023 14
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
From CNS
4
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
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.
04/12/2023 gastro intestinal reflexes 15
……….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.
04/12/2023 gastro intestinal reflexes 16
………….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.
04/12/2023 gastro intestinal reflexes 17
…………..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.
04/12/2023 gastro intestinal reflexes 18
……………..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.
04/12/2023 gastro intestinal reflexes 19
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.
04/12/2023 gastro intestinal reflexes 20
Defecation reflexes cont’d
04/12/2023 21Fig 6. anatomical view of rectum and anal channel
…………..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.
04/12/2023 22gastro intestinal reflexes
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.
04/12/2023 23gastro intestinal reflexes
04/12/2023Fig7. defecation reflexes
24
…………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.
04/12/2023 25gastro intestinal reflexes
04/12/2023 26gastro intestinal reflexes
………………….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.
04/12/2023 27gastro intestinal reflexes
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.
04/12/2023 28gastro intestinal reflexes
…………….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.)
04/12/2023 gastro intestinal reflexes 29
04/12/2023 gastro intestinal reflexes 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)
04/12/2023 gastro intestinal reflexes 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 sickness3.Afferent impulses from viscera stimulate vomiting
center via NTS.• Vomiting induced in visceral disease.
04/12/2023 gastro intestinal reflexes 32
04/12/2023 gastro intestinal reflexes
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
33
top related