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40 Cards in this Set
- Front
- Back
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What is the function of he Interstitial Cell of Cajal and where are they located?
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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 |
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What cells act as an intermediate between muscle cells and neurons in the gut via their processes?
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Interstitial Cells of Cajal
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What determines the amplitude and duration of a plateau phase in slow waves?
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the magnitude of Ca2+ influx
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What can modify the plateau of a slow wave?
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Hormones and NTs
(excitatory increase amplitude and duration - ACh, Sub P, CCK) (inhibitory decrease amplitude and duration - VIP) |
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When does contraction occur?
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Only when plateau potential exceeds threshold for voltage-activated Ca2+ channel
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When are "spikes" usually seen?
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above threshold in intestinal cells
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What reverses membrane potential in a "spike"?
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inactivation of voltage-sensitive Ca2+ channels, and opening of K+ channels
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Are spike potentials always accompanied by contraction?
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Yes
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Are spike potentials necessary for contraction?
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No -- I do not understand why??? pg. 579
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What is the amplitude of contraction determined by?
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the # of spikes
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What sets the maximal rate of contraction in the gut?
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slow waves
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What characterized Unitary (gut) muscle?
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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 |
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Describe the nerves in longitudinal muscle (thinner layer) .
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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) |
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Describe the nerves in circular muscle (thicker layer).
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1) many neurons of varied type
2) release NT from varicosities 3) spread of excitation or inhibition thru gap junctions 4) relaxation predominates (VIP) |
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Describe reciprocal innervation.
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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.
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What are the three patterns of motility in the gut?
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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) |
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Is swallowing voluntary or involuntary?
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both -- starts voluntary then becomes reflexive
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Three phases of the swallow:
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1) Oral/voluntary
2) Pharyngeal 3) Esophageal (includes primary and secondary peristalsis) |
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What is the difference between primary and secondary peristalsis?
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primary - follows pharyngeal and oral phase and is initiated by distension from bolus
secondary - via chemical stimulation of the mucosa |
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What nerves are responsible for mediating the neural reflex of peristalsis in the esophagus?
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the vagus (both efferent and afferent)
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What kind of muscle makes up the upper 1/3 of esophagus and what innervates it?
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Skeletal - innervated directly by vagus (ACh)
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What kind of muscle makes up the lower 1/3 of esophagus and what innervates it?
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Smooth muscle - innervated indirectly by vagus through enteric NS (ACh - excitatory, or VIP/NO - inhibitory)
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What fibers make up the middle 1/3 of esophagus?
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mixed skeletal and smooth muscle fibers
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What mediates the relaxation of the LES?
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VIP/NO from the myenteric plexus
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What are the major functions of the stomach?
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1) storage!! (reservoir)
2) grind and mix food 3) regulate delivery of nutrients to small intestine |
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What is unique about the fundus and orad corpus regions of the stomach?
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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
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Description and function of Proximal stomach:
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1) muscle is thin
2) reservoir function 3) acid secretion |
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Description and function of Corpus (mid and caudad) stomach:
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1) muscle layer thicker
2) storage and mixing functions |
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Description and function of Antrum stomach:
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1) very thick muscle layer
2) pump/grinding 3) little secretion |
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Description and function of Pyloric Sphincter:
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1) controls particle size and regulates emptying
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What happens to the duration and amplitude of contractions as you proceed down the stomach distally?
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the contractions increase in amplitude and duration
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How frequent are slow waves in the stomach?
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3/min
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What part of the stomach has the strongest and longest contractions?
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Terminal (caudad) antrum
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Explain receptive relaxation.
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1) peristaltic wave in stomach relaxes the LES, fundus, and orad corpus
2) involves vagal preganglionic nerves and myenteric relaxant nerves w/ VIP/NOS |
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Where are pacemaker cells located?
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in the corpus of the stomach
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How much material (approx) is pushed thru the pyloric sphincter each time it opens?
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10-15 ml
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Describe Gastric Emptying:
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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 |
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Do chemoreceptors in intestine speed or slow down gastric emptying?
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Slow down
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Components of Chyme which slow gastric emptying:
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1) Acid
2) Lipid digestion products (with CCK, GIP) ** most effective!! 3) Protein digestion products (with CCK, gastrin) 4) Hypo or Hyper-osmotic solutions |
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Novel site of action for CCK during gastric emptying:
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on sensory mechanoreceptors in stomach - activate vasovagal reflex - VIP - relaxation of fundus - reduce emptying
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