Gastrointestinal Motility: Key Concepts and Mechanisms
GASTROINTESTINAL PHYSIOLOGY
Chapter-III
(Gastrointestinal Motility)
Ass. Prof. Dr. Emre Hamurtekin
EMU Faculty of Pharmacy
PERISTALTIS
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It occurs in all
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SEGMENTATION
A segment of bowel contracts at both ends and a second
contraction occurs in the center of the segment.
It is designed to retard the movement of the intestinal
contents.
It provides mixing of the intestinal contents with the
digestive juice.
BASIC ELECTRICAL ACTIVITY
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The BER itself rarely causes muscle contraction.
Spike potentials over the depolarizing portion of the
BER waves increase muscle tension.
BER coordinates peristaltic activity and setting the
rhythm of segmentation.
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MIGRATING MOTOR COMPLEX
A modification in the electrical and motor activity
in smooth muscle of GI tract
between periods of
digestion.
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MASTICATION & SWALLOWING
Mastication (chewing)
:
Breaks up large food particles
Mixes the food with the salivary secretions
Swallowing
is a reflex response triggered by
afferent impulses
in,
trigeminal,
glossopharyngeal,
vagus nerve
efferent impulses
in
trigeminal,
facial,
hypoglossal nerve
LOWER ESOPHAGEAL SPHINCTER
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The tone of the LES
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GASTRIC MOTILITY and EMPTYING
Receptive relaxation
:
Relaxation of the fundus and the upper part of the body of
the stomach to accommodate the food, when food enters
the stomach.
After receptive relaxation, peristaltis begins and mixes the
food and permits the semiliquid portions to pass through
the pylorus.
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Gastric emptying rate
depends on;
Type of food ingested
(carbohydrate rich > protein rich > fat rich)
Osmotic pressure of the material entering the duodenum
Hyperosmolality decreases the gastric emptying
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VOMITING
Some main reasons that trigger vomiting
:
Irritation of the upper GI tract mucosa
Motion sickness
Emotionally charged stimuli
Chemical agents in the circulation stimulating CTZ
Chemoreceptor Trigger Zone (CTZ):
Located in the
Area Postrema
in the medulla
Not protected by blood-brain barrier
Includes chemoreceptor cells that can be stimulated
by certain chemical agents.
Vomiting is an example of
central regulation
of GI
motility.
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INTESTINAL MOTILITY
There are 3 types of smooth muscle contractions
:
Peristaltis
Segmentation contractions
Tonic contractions
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COLON MOTILITY
Motility in this segment is slow.
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Relaxation of cecum and increase in the passage of small
intestinal content
when food leaves the stomach.
3 types of colonic smooth muscle contractions
:
Peristaltic waves
Segmentation contractions
Mass action contraction
*** (occurs only in the colon)
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Simultaneous contractions over large confluent areas occurs
about 10 times / day that move the material from one portion of
the colon to another.
ILEOCECAL VALVE
DEFECATION
DEFECATION
Distension of rectum with feces initiates reflex
contractions and desire to defecate.
Internal anal sphincter relaxes when the rectum is
distended.
Internal anal sphincter
:
Sympathetic: excitatory
Parasympathetic: inhibitory
External anal sphincter
:
Skeletal muscle
Pudendal nerve
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Contractions of the rectum and desire to defecate initiated
by
distention of stomach by food
THE END
Gastrointestinal motility involves various processes like peristalsis, segmentation, basic electrical activity, and the migrating motor complex. Peristalsis is the reflex response to gut wall stretching, while segmentation helps mix intestinal contents and digestive juices. Basic Electrical Rhythm (BER) coordinates peristaltic activity, and the migrating motor complex modifies smooth muscle activity during digestion cycles. Mouth and esophagus functions include mastication and swallowing. The lower esophageal sphincter is tonically active but relaxes during swallowing.
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Presentation Transcript
GASTROINTESTINAL PHYSIOLOGY Chapter-III (Gastrointestinal Motility) Ass. Prof. Dr. Emre Hamurtekin EMU Faculty of Pharmacy
PERISTALTIS Peristaltis is a reflex response initiated when the gut wall is stretched. It occurs in all parts of the GI tract.
SEGMENTATION A segment of bowel contracts at both ends and a second contraction occurs in the center of the segment. It is designed to retard the movement of the intestinal contents. It provides mixing of the intestinal contents with the digestive juice.
BASIC ELECTRICAL ACTIVITY The spontaneous rythmic fluctuations of the membrane potential of the smooth muscle of GI tract between about -65 and -45 mV is called basic electrical rhythm, BER . The BER itself rarely causes muscle contraction. Spike potentials over the depolarizing portion of the BER waves increase muscle tension. BER coordinates peristaltic activity and setting the rhythm of segmentation. Ach increases the number of spikes and the tension of the smooth muscle, but epinephrine decreases.
MIGRATING MOTOR COMPLEX A modification in the electrical and motor activity in smooth muscle of GI tract between periods of digestion. The cycles (MMC) of motor activity migrate from the stomach to the distal ileum. Phases of MMC: Phase I: No spike potentials, no contractions Phase II: Irregular spike potentials & contractions Phase III: Regular spike potentials & contractions The MMCs are initiated by motilin.
MASTICATION & SWALLOWING Mastication (chewing): Breaks up large food particles Mixes the food with the salivary secretions Swallowing is a reflex response triggered by afferent impulses in, trigeminal, glossopharyngeal, vagus nerve efferent impulses in trigeminal, facial, hypoglossal nerve
LOWER ESOPHAGEAL SPHINCTER LES is tonically active but relaxes on swallowing. The tone of the LES is under neural control. Ach ...intrinsic sphincter contraction NO & VIP ....intrinsic sphincter relaxation
GASTRIC MOTILITY and EMPTYING Receptive relaxation: Relaxation of the fundus and the upper part of the body of the stomach to accommodate the food, when food enters the stomach. After receptive relaxation, peristaltis begins and mixes the food and permits the semiliquid portions to pass through the pylorus. CCK and secretin stimulates the pyloric sphincter and prevents regurgitation. Gastric emptying rate depends on; Type of food ingested (carbohydrate rich > protein rich > fat rich) Osmotic pressure of the material entering the duodenum Hyperosmolality decreases the gastric emptying Fats, carbohydrates and acid in the duodenum inhibit gastric acid / pepsin secretion and gastric motility. CCK also can inhibit gastric emptying.
VOMITING Some main reasons that trigger vomiting: Irritation of the upper GI tract mucosa Motion sickness Emotionally charged stimuli Chemical agents in the circulation stimulating CTZ Chemoreceptor Trigger Zone (CTZ): Located in the Area Postrema in the medulla Not protected by blood-brain barrier Includes chemoreceptor cells that can be stimulated by certain chemical agents. Vomiting is an example of central regulation of GI motility.
INTESTINAL MOTILITY There are 3 types of smooth muscle contractions: Peristaltis Segmentation contractions Tonic contractions Tonic contractions are relatively prolonged contractions that in effect isolate one segment of the intestine from another. Segmentation contractions Tonic contractions retard transit time
COLON MOTILITY Motility in this segment is slow. Ileocecal valve is shut by the increases in colonic pressure and opened increases in ileal pressure. Gastroileal reflex: Relaxation of cecum and increase in the passage of small intestinal content when food leaves the stomach. 3 types of colonic smooth muscle contractions: Peristaltic waves Segmentation contractions Mass action contraction*** (occurs only in the colon) Mass action contraction: Simultaneous contractions over large confluent areas occurs about 10 times / day that move the material from one portion of the colon to another.
DEFECATION Distension of rectum with feces initiates reflex contractions and desire to defecate. Internal anal sphincter relaxes when the rectum is distended. Internal anal sphincter: Sympathetic: excitatory Parasympathetic: inhibitory External anal sphincter: Skeletal muscle Pudendal nerve Gastrocolic reflex: Contractions of the rectum and desire to defecate initiated by distention of stomach by food
