GI Motility Flashcards
What parts of the GI system are composed of striated muscle?
- Mouth
- Pharynx
- Upper esophagus
- External Anal Sphincter
What are the 2 types of contractions of GI smooth muscles?
- Phasic Contractions
2. Tonic Contractions
What are phasic contractions?
- Regularly repeated contractions
2. Cause mixing & propelling of GI contents
Where do phasic contractions happen?
Stomach & Small Intestine
What are Tonic Contractions?
- Continous contractions
2. Only Relax under neural stimulation
Where do tonic contractions happen?
Upper stomach & the sphincters
What type of cell generates slow waves?
Interstitial cells of Cajal (ICC) - have gap junctions
Electrical activity in the GI tract is located where?
Between the long & circular muscle layers (mid stomach to rectum)
What two enzymes/hormones are released from the PNS and act on the myenteric plexus causing the depolarization of slow waves & contraction?
- Ach
2. Substance P
What other 2 hormones can also depolarize slow waves and cause contractions?
- Cholecystokinin (CCK)
2. Gastrin
The parasympathetic NS enhances motility & secretions through which 2 plexus’s?
- Myenteric
2. Submucosal
The sympathetic NS reduces motility & secretions through which nervous system?
The enteric NS
How does the sympathetic NS reduce motility & secretions?
Inhibitory motor neurons get stimulated and release VIP (vasoactive intestinal peptide) and NO –> hyperpolarize the slow waves –> relaxes smooth muscle
What is peristalsis?
Sequential contraction of muscles in response to stretching of gut wall
What does this describe? ‘Long periods of rest with short periods of waves of contractions’
Migrating Myoelectric Complex (MMC)
Where does the MMC start and continue its short periods of contractions to?
Starts in the mid-stomach & continues to the terminal ileum during each cycle
What is the function of the MMC?
- Function is “housekeeping”
- Undigested material and bacteria swept out of stomach and sm. intestine into colon,
- Protects delicate upper GI tract from damage, and gets bacteria in colon in a drier environment which is less hospitable to the bacteria
Out of the 4 phases of MMC which one is the most important?
- Phase III
- Mo cells of the small intestine release motilin into circulation
- Motilin causes strong sequential contractions
What are the 3 stages of swallowing?
- Oral Stage/Buccal Phase
- Pharyngeal Stage
- Esophageal Stage
What happens during the oral stage of swallowing?
- Bolus of food moved from back of mouth into pharyngeal region
- Touch receptors in this area stimulate swallowing
What happens during the pharyngeal stage of swallowing?
- Bolus moves to back of pharynx
- Larynx moves towards epiglottis
- Upper esophageal sphincter (UES) relaxes
What happens during the Esophageal stage of swallowing?
- Bolus enters esophagus where peristalsis propels food down the GI tract through lower esophageal sphincter (LES) into stomach
- LES normally has high resting muscle tone
What is receptive relaxation?
- As bolus enters stomach, relaxation increases stomach size to accommodate meal called receptive relaxation
- Vagal mediation thru release of VIP (vasoactive intestinal peptide)
As the stomach fills, what stimulates contraction?
- Stretch
2. Chemical Contents