BIOL 2P93 Lecture Notes - Constipation, Gastroparesis, Bacs

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GI Motility
I. Introduction
a. Function of GI Motility: to propel, grind, mix, & store its contents
i. Functional segments may not always conform neatly w/ anatomical ones
b. Structure: a series of pumps, conduits, reservoirs & gates
c. Neural Control
i. Extrinsic
1. Parasympathetic: enters thru vagus (sacral n. at end)
a. NTs—acetylcholine & substance P
b. stimulation => increased activity
2. Sympathetic—enters thru sympathetic nerve ganglion
a. NTs—NO & VIP
b. stimulation => inhibition (decreased activity)
ii. Intrinsic
1. web of neurons w/in wall of GI tract; in communication w/
sympathetic & parasympathetic systems
2. extensive contact between neurons & w/ myocytes
3. key role in coordinating GI smooth mm. fxn
4. can act independently of CNS
5. Myenteric Plexus—between 2 layers of muscularis; very rich
innervation
iii. Neural Stimulation
1. direct contact—cells are directly synapsed upon by nn.
2. indirect contact—cells that receive electronic signals thru
adjacent cells
d. Types of Contractions
i. Phasic contractions—result from momentary stimulation and are used for
pumping
ii. Tonic contractions—result in continuous pressure and must be relaxed to
allow gating (sphincters)
e. Patterns of Phasic Contractions
i. Primarily Propulsive—progressive waves which completely occlude the
lumen & propel food in a given direction
ii. Mixing & Propulsive—progressive waves which fail to completely
occlude the lumen & leave some food behind
iii. Mixing & Grinding—interrupted progressive waves which may be
discoordinated => segmental contractions; fxn is to mix & grind
f. Slow Wave
i. Key for generating contractions from stomach downwards
ii. Generated by specialized cells (interstitial cells of Cajal (ICC))
iii. Begin in stomach and travel downward thru GI tract
iv. Frequency is characteristic of different parts of GI
v. Contractions => when spike potentials occur during slow waves (not every
slow wave => a contraction!)
g. Propagation of Contractions
1
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