IV MOTILITY OFTHE SMALL INTESTINE
1 IV MOTILITY OF THE SMALL INTESTINE
Function of Intestinal Motility (I)To mix chyme with digestive secretion (2)To bring fresh chyme into contact with the absorptive surface of the microvilli (To propel chyme toward the colon
2 Function of Intestinal Motility (1)To mix chyme with digestive secretion (2)To bring fresh chyme into contact with the absorptive surface of the microvili (3)To propel chyme toward the colon
Contractions of Intestinal Smooth Museles Occur automatically in Slow waves response to endogenous 28 pacemaker activity Rhythm of contractions is mV paced by graded depolarizations called slow waves 5 sec Slow waves produced by interstitial cells of Cajal Slow waves spread from I smooth muscle cell to another through nexuses 3
3 Contractions of Intestinal Smooth Muscles • Occur automatically in response to endogenous pacemaker activity. • Rhythm of contractions is paced by graded depolarizations called slow waves. •Slow waves produced by interstitial cells of Cajal. •Slow waves spread from 1 smooth muscle cell to another through nexuses
Cells and Electrical Events inthe Muscularis Copyright e The MoGraw-Hill Companies, Inc. Permission required for reproduction or display. Structures Functions Production Interstitial of slow waves cells of Cajal Conduction of slow waves to smooth muscle Depolarization Smooth and opening of muscle Caz+ channels, cells production of action potentials Autonomic Neural input to ICC and smooth axon muscle
4 Cells and Electrical Events in the Muscularis Insert fig. 18.16
Stuart Ira Fox, Human Physiology, 6e. Copyright e 1999 The McGraw-Hill Companies, Inc. All rights reserved. Electrical Activity in Intestinal smooth muscle Pacesetter potential Membrane potential Smooth muscle contraction Tension 0421.PC
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Contractions of Intestinal Smooth muscles When slow waves above threshold, it triggers APs bi opening of VG Ca2+ channels ° Inward flow of ca2+ Produces the upward depolarization phase Stimulates contraction of smooth muscle Repolarization VG K channels open Slow waves decrease in amplitude as they are conducted May stimulate contraction in proportion to the magnitude of depolarization
6 • When slow waves above threshold, it triggers APs by opening of VG Ca2+ channels. • Inward flow of Ca2+: • Produces the upward depolarization phase. • Stimulates contraction of smooth muscle. • Repolarization: • VG K+ channels open. • Slow waves decrease in amplitude as they are conducted. • May stimulate contraction in proportion to the magnitude of depolarization. Contractions of Intestinal Smooth Muscles
+30 an Vg ca++ cha 55 Intestinal Smooth Muscle Action Potential 7
7 -55 +30 Vg Ca++ Channel Vg K+ Channel Intestinal Smooth Muscle Action Potential
Contractions of Intestinal Smooth muscles Parasympathetic NS, stretch and gastrin increase the amplitude of slow waves Stimulate aps sNS decrease aps
8 • Parasympathetic NS, stretch and gastrin increase the amplitude of slow waves. • Stimulate APs. • SNS decrease APs. Contractions of Intestinal Smooth Muscles
Types of small intestinal movement 1. Tonic contraction: the base of the other contractio 2. Segmentation contractions (1) def. When a portion of the small intestine becomes distended with chyme the stretch of the intestinal wall elicits a rhythmical contraction and relaxation of localized circular muscles spaced at intervals along the intestine, (2) function mix the chyme with the digestive juice increase its exposure to the mucosal surface
9 1. Tonic contraction: the base of the other contractions 2. Segmentation contractions (1) def. When a portion of the small intestine becomes distended with chyme, the stretch of the intestinal wall elicits a rhythmical contraction and relaxation of localized circular muscles spaced at intervals along the intestine, (2) function: mix the chyme with the digestive juice increase its exposure to the mucosal surface Types of small intestinal movement
Types of small intestinal movement 3. Peristalsis: propels the small intestinal contents towards the large intestines peristaltic rush: initiated by the harmful stimulation 4. MMC Occurs during fasting state moves any undigested material still remaining in the small intestine into the large intestine prevents bacteria from remaining in the small intestine long enough to grow and multiply excessively 10
10 3. Peristalsis: propels the small intestinal contents towards the large intestines peristaltic rush：initiated by the harmful stimulation 4. MMC: Occurs during fasting state moves any undigested material still remaining in the small intestine into the large intestine prevents bacteria from remaining in the small intestine long enough to grow and multiply excessively Types of small intestinal movement