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40 Cards in this Set

  • Front
  • Back
What is the function of he Interstitial Cell of Cajal and where are they located?
1) pacemaker cells of the gut - oscillate at a higher frequency than the intrinsic rate of SM cells
2) located at myenteric and submucosal juctions
What cells act as an intermediate between muscle cells and neurons in the gut via their processes?
Interstitial Cells of Cajal
What determines the amplitude and duration of a plateau phase in slow waves?
the magnitude of Ca2+ influx
What can modify the plateau of a slow wave?
Hormones and NTs

(excitatory increase amplitude and duration - ACh, Sub P, CCK)
(inhibitory decrease amplitude and duration - VIP)
When does contraction occur?
Only when plateau potential exceeds threshold for voltage-activated Ca2+ channel
When are "spikes" usually seen?
above threshold in intestinal cells
What reverses membrane potential in a "spike"?
inactivation of voltage-sensitive Ca2+ channels, and opening of K+ channels
Are spike potentials always accompanied by contraction?
Are spike potentials necessary for contraction?
No -- I do not understand why??? pg. 579
What is the amplitude of contraction determined by?
the # of spikes
What sets the maximal rate of contraction in the gut?
slow waves
What characterized Unitary (gut) muscle?
1) less tightly controlled by release of NT from nerve varicosities of passing neurons
2) more gap junctions
3) spontaneously active
4) no true neuromuscular junctions
Describe the nerves in longitudinal muscle (thinner layer) .
1) very few nerve fibers
2) contracted by ACh from myenteric plexus
3) relaxation mainly due to inhibition of ACh release (very few inhibitory nerve fibers)
Describe the nerves in circular muscle (thicker layer).
1) many neurons of varied type
2) release NT from varicosities
3) spread of excitation or inhibition thru gap junctions
4) relaxation predominates (VIP)
Describe reciprocal innervation.
Circular muscle relaxes when longitudinal muscle contracts to move food down the GI tract. Comprises the Law of the Intestine and is an example of a Short Arc reflex - Peristaltic Reflex.
What are the three patterns of motility in the gut?
1) tonic or sustained contraction (sphincters) - neural innervation usually inhibitory
2) segmental contraction (mixing in small intestine and colon)
3) peristaltic contractions (propulsive, propogated contractions; mvmt toward anus; found throughout gut except proximal stomach)
Is swallowing voluntary or involuntary?
both -- starts voluntary then becomes reflexive
Three phases of the swallow:
1) Oral/voluntary
2) Pharyngeal
3) Esophageal (includes primary and secondary peristalsis)
What is the difference between primary and secondary peristalsis?
primary - follows pharyngeal and oral phase and is initiated by distension from bolus
secondary - via chemical stimulation of the mucosa
What nerves are responsible for mediating the neural reflex of peristalsis in the esophagus?
the vagus (both efferent and afferent)
What kind of muscle makes up the upper 1/3 of esophagus and what innervates it?
Skeletal - innervated directly by vagus (ACh)
What kind of muscle makes up the lower 1/3 of esophagus and what innervates it?
Smooth muscle - innervated indirectly by vagus through enteric NS (ACh - excitatory, or VIP/NO - inhibitory)
What fibers make up the middle 1/3 of esophagus?
mixed skeletal and smooth muscle fibers
What mediates the relaxation of the LES?
VIP/NO from the myenteric plexus
What are the major functions of the stomach?
1) storage!! (reservoir)
2) grind and mix food
3) regulate delivery of nutrients to small intestine
What is unique about the fundus and orad corpus regions of the stomach?
they are tonically contracted at rest due to low resting membrane potential (-48 mv) -- allow Ca2+ channels to remain open -- NO SLOW WAVES OR MYOELECTRICAL RHYTHM
Description and function of Proximal stomach:
1) muscle is thin
2) reservoir function
3) acid secretion
Description and function of Corpus (mid and caudad) stomach:
1) muscle layer thicker
2) storage and mixing functions
Description and function of Antrum stomach:
1) very thick muscle layer
2) pump/grinding
3) little secretion
Description and function of Pyloric Sphincter:
1) controls particle size and regulates emptying
What happens to the duration and amplitude of contractions as you proceed down the stomach distally?
the contractions increase in amplitude and duration
How frequent are slow waves in the stomach?
What part of the stomach has the strongest and longest contractions?
Terminal (caudad) antrum
Explain receptive relaxation.
1) peristaltic wave in stomach relaxes the LES, fundus, and orad corpus
2) involves vagal preganglionic nerves and myenteric relaxant nerves w/ VIP/NOS
Where are pacemaker cells located?
in the corpus of the stomach
How much material (approx) is pushed thru the pyloric sphincter each time it opens?
10-15 ml
Describe Gastric Emptying:
1) liquids quicker than solids
2) water is fastest liquid
3) distension of stomach increases the rate of emptying (mechanoreceptors) - short arc and long arc (vago-vagal) reflexes
Do chemoreceptors in intestine speed or slow down gastric emptying?
Slow down
Components of Chyme which slow gastric emptying:
1) Acid
2) Lipid digestion products (with CCK, GIP) ** most effective!!
3) Protein digestion products (with CCK, gastrin)
4) Hypo or Hyper-osmotic solutions
Novel site of action for CCK during gastric emptying:
on sensory mechanoreceptors in stomach - activate vasovagal reflex - VIP - relaxation of fundus - reduce emptying