GASTROINTESTINAL PHYSIOLOGY ChapterIII Gastrointestinal Motility Ass Prof Dr
- Slides: 19
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 m. V 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.
MOUTH & ESOPHAGUS
MASTICATION & SWALLOWING �Mastication (chewing): Ø Breaks up large food particles Ø Mixes the food with the salivary secretions �Swallowing is a reflex response triggered by afferent impulses in, q trigeminal, q glossopharyngeal, q vagus nerve efferent impulses in q trigeminal, q facial, q 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
STOMACH
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; q Type of food ingested Ø (carbohydrate rich > protein rich > fat rich) q Osmotic pressure of the material entering the duodenum Ø 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: Ø Irritation of the upper GI tract mucosa Ø Motion sickness Ø Emotionally charged stimuli Ø Chemical agents in the circulation stimulating CTZ �Chemoreceptor Trigger Zone (CTZ): ü Located in the Area Postrema in the medulla ü Not protected by blood-brain barrier ü Includes chemoreceptor cells that can be stimulated by certain chemical agents. �Vomiting is an example of central regulation of GI motility.
SMALL INTESTINE
INTESTINAL MOTILITY �There are 3 types of smooth muscle contractions: v. Peristaltis v. Segmentation contractions v. Tonic contractions �Tonic contractions are relatively prolonged contractions that in effect isolate one segment of the intestine from another. �Segmentation contractions retard Tonic contractions transit time
COLON
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: Ø Peristaltic waves Ø Segmentation contractions Ø 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.
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 � Gastrocolic reflex: Contractions of the rectum and desire to defecate initiated by distention of stomach by food
THE END
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