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.
Pressures in swallowing
High pressures are generated behind bolus to propel it forward. Gravity helps. Lower esophageal sphincter relaxes, stomach relaxes to allow food to enter.
Where is the squamocolumnar junction?
At the LES. High pressure zone, not a true sphincter.
Pressure of LES
20mmHg, relaxes with swallow.
Two functional parts of stomach
Fundus/body- receptive relaxation, reservoir, regulates liquid emptying.
Antrum- Grinds and mixes, vagally mediated. Regulates emptying of solids.
MMC
Migrating motor complex. Kicks in between meals to send electrical waves through GI system, induces contractions to sweep to prep for next meal. Process starts with ICCs (interstitial cells of cajal)
ICC Location
Directly above smooth muscle ti cause depolarization and activation of L-type ca channels.
Contraction during fasting vs fed state
Fasting mediated by MMC, cyclic contractions. Fed state has segmental contractions to promote mixing and absorption.
What excites peristalsis? Inhibits?
ACh, tachykinin, gastrin, motilin. VIP, NO inhibit.
Function of the colon
Absorption of water, propulsion of contents, storage and expulsiion of feces.
Speed of colonic transit?
Slower than small bowel
Contraction types in colon
Low amplitude: frequent (>100/day), to transport fluid contents. Associated with distension and flatus.
High amplitude contractions: Infrequent, associated with mass movement and defecation.
Gastrocolic reflex
Distension of the stomach increases mass movements in colon. Mediated by CCK and gastrin.
Defecation
Internal anal sphincter relaxation, external anal sphincter contraction, anorectal angle straightening as pelvic floor drops.
Tone maintained by IAS vs EAS?
70-80% IAS.
Function of the puborectalis muscle
Contraction straightens the anorectal angle.
Continence requires:
Anal sphincter integrity, puborectalis, anal sensation, nerve integrity.
