GI Motility Flashcards
Location of smooth muscle in GI tract
Lower 2/3 of esophagus, stomach, small and large intestine, internal anal sphincter.
Location of skeletal muscle in the Gi tract
Pharynx, upper esophageal sphincter, upper 1/3 of esophageal body, external anal sphincter.
Slow Waves
Constant background rhythm, propagate down GI tract, control the timing of phasic reactions. Every organ has characteristic slow wave activity.
Which organ in the GI tract has the highest slow wave activity?
Small intestine, then colon, then stomach.
Do slow waves always cause contractions?
No, need additional action potentials to reach contraction threshold.
Interstitial Cells of Cajal
The pacemaker cells of the gut.
Do contractions in the gut always increase transit?
No.
Tonic contractions
Hold sphincters closed. Mainly utilized by storage organs of the GI tract. Require less energy.
Phasic Contractions
Can be peristaltic, anti-peristaltic, or segmenting.
Two major types of small intestine contractions
Peristalsis: Propagative, slow
Segmentation: Major contractile action in SI, contraction of circular muscle. One area contracts, then another area does.
How is peristalsis controlled?
Serotonin plays a big role, NO can mediate distal relaxation
Is the LES a true sphincter?
No, just a high pressure zone.
Sphincter of Oddi
Controls Pancreatic/Gall bladder secretion
Upper esophageal sphincter
Composed of striated muscle. Unique (with the exception of the external anal sphincter.
Where is swallowing coordinated? What occurs?
The medulla. Nasopharynx closes, breathing is inhibited, laryngeal muscles contract to close the glottis and elevate larynx. Peristalsis begins in pharynx to propel food backwards. UES relaxes allowing bolus to enter esophagus.
