2 Motility Of The GI Tract Flashcards
Digestive process
GI motility
Ingestion
Propulsion
Mechanical digestion
Chemical digestion
Absorption
Defecation
Lines the lumen of the GI tract
Mucosa
Fx of submucosa
Relays info to and away from the mucosa
Fx of muscularis external
Motility of the GI tract
What do parietal cells secrete?
HCl
Intrinsic factor
Chief cells secrete ______.
Pepsinogen
Gastrin is secreted by ________.
Enteroendocrine cells
Specialized group of cells in the intestinal wall
Involved in transmission of info from enteric neurons to smooth m.
Interstitial cells of Cajal (ICCs)
What are the pacemaker cells in the intestinal wall?
What do they generate?
ICCs
Generate the basic electrical rhythm (slow-wave activity) of GI smooth m.
What changes do the ICC cells undergo?
Why?
Cyclic changes in the membrane potential
Due to unique ion channels that periodically open and produce inward (pacemaker) currents that generate the slow wave activity
Two basic electrical waves in the smooth m of the GI tract
Slow waves
Spike potentials
Slow waves make it possible for contractions to be stimulated more _________ by raising the RMP ________ to threshold and less _________.
Easily
Closer
Negative
Where is the rate of slow waves lowest?
Highest?
Stomach (3/min)
Duodenum (12/min)
T/F: slow waves are true action potentials.
FALSE
Not AP, instead they are slow changes in the RMP
Not sufficient to completely depolarize the membrane and stimulate contractions
Spike waves are true_____.
Action potentials
What stimulates spike waves (depolarization)?
Stretching of the muscle
ACh
Parasympathetics
Several specific GI hormones
When do spike waves occur?
Automatically when the RMP of the GI smooth m is more positive than about -40 millivolts
The spike potentials last ____ to ____ times as long in GI muscle as the AP in large nerve fibers.
10 to 40 times longer
Hyperpolarization is stimulated by _____.
NE or epinephrine on the fiber membrane
Sympathetic nerves that secrete NE at their endings
What is the RMP in the gut?
-56 millivolts
Depolarization in the GI tract is stimulated by _____.
How is this released?
What receptors does it act through?
What does it do?
ACh
Released by postganglionic axons
Acts through muscarinic receptors
Increases the amplitude and duration of the slow waves
T/F: slow waves cause Ca to enter the smooth m fiber.
FALSE
Slow waves cause Na to enter the smooth m
What ion causes the contraction of smooth m in the GI tract?
Calcium
When are spike potentials generated?
Why?
At the peak of slow waves
To allow enough Ca ions to enter the fibers and cause a contraction