GI 5: Regulation of Motility Flashcards
____cells of the ___ are the electrical pacemakers of the GI tract
interstitial; cajal
interstitial cells of the cajal are modified smooth muscle cells that don’t contract, but undergo _____
slow wave
do slow waves always reach threshold?
no
what are slow waves?
undulating changes in resting membrane potential
slow waves do not cause ______ by themselves, but set the _____
muscle contractions; maximal contraction frequency
what 4 things determine if slow wave threshold is met?
- stretch
- presence of food (chemo)
- parasympathetic stimulation
- hormones
can you have more thresholds than slow waves?
no
with decreased ap frequency, there is less influx of __ ions and decreased tone
ca
when slow waves are combined with excitatory signals , a __ is reached
threshold
are ca channels slow or fast to open/close, means their ap last ___
slow; longer
slow waves w/o ap can only let ___ ions in, so contraction ___happen
na; can’t
what are. the 3 contractile patterns
- peristalsis
- segmentation
- tonic contraction
what is peristalsis and where does it occur?
smooth muscle activity where there is relaxation before the food blows and contraction behind it. Occurs along the entire GI tract
peristalsis results in the ___ of the bolus
forward movement
what is segmentation and where does it occur?
stationary contraction and relaxation of intestinal segments. occurs in the small and large intestines
in segmentation, there is ___ net movement and results of ___ of the food bolus
no; mixing
what is tonic contraction? where does it occur?
separation of structures and functions along the digestive tract. occurs at GI spinsters
t/f there is very little forward movement in segmentation
true
t/f peristalsis is a polarized process
true
there is contraction ____cm behind the food bolus
2-3
ahead of the food bolus the is ___ relaxation
receptive
when excited, the myenteric plexus increases what 4 things?
- tone of gut wall
- contraction intensity
- contraction frequency
- velocity of contraction
cholecystokinin (CCk) secretion is stimulated by ____ , ___ and ___and is secreted from the ____ which moderately ____ stomach contractions
protein, fat, and acids; I cells of the duodenum, jejunum and ileum; inhibits
glucose-dependent insulinotropic peptide is stimulated by ___, ___ and ___ and is secreted from the ___ cells of the ___ and ___ parts of the small intestine
fat, amino acids, carbohydrates; K; duodenum and jejunum
the action of the glucose dependent insulinotropic peptide moderately ____ stomach contractions
inhibits
motion secretion is stimulated by cyclic release during ____. It is secreted by the ____ cells of the ___ part of the small intestine
fasting; M ; duodenum
where does the voluntary stage of swallowing occur? what allows this area to act voluntarily?
mouth to pharnyx (made of skeletal muscle)
what stage of swallowing is initiated by receptors in the pharynx, leading to soft palate and uvula elevation, epiglottis closing and relaxation of the esophageal spinster
pharyngeal (involuntary)
what are the 3 stages of swallowing
and are they voluntary / involuntary?
- voluntary (mouth to pharynx)
- pharyngeal (involuntary)
- esophageal (involuntary )
the elevation of the soft palate during swallowing prevents ___
food getting into the nasal passageway
what are the 3 types of motility involved in the esophageal stage of swallowing?
- primary peristalsis
- secondary peristalsis
- tonic contractions
t/f peristaltic waves in the esophagus go the length of the esophagus
true
primary peristalsis is a continuation of peristalsis waves form the ___
pharynx
what happens in primary peristalsis?
food pushed down the esophagus
how long does one wave take in primary peristalsis?
9 sec
what is the stimuli for primary peristalsis?
pharynx distention
secondary peristalsis is initiated by ___
esophagus distention
secondary peristalsis only occurs if
primary wasn’t enough to get food to the stomach
what are the 2 sphincters does the esophagus have?
upper and lower esophageal sphincters
contraction of the upper esophageal sphincter reduces ___
air intake
contraction of the lower esophageal sphincter reduces
acid reflux
what is dysphagia?
difficulty swallowing
dysphagia is often due to pathophysiology of the ___
esophagus
dysphagia can be caused by ____, which is the loss of peristalsis in the lower esophagus and/or failure of the LES to relax and let bolus into the stomach
achalasia
what is GERD?
increased frequency of LES opening, even w/o food bolus
achalasia may be caused by the degeneration of neurons in the ____ plexus of the esophageal wall, especially the ___ neurons that induce relaxation of the LES
myenteric; inhibitory
what are the 3 functions of the stomach?
- storage of large quantity of food
- mixing of food bolus with gastric juice
- slow, regulated emptying of chyme into the SM Int to improve digestion and absorption
chyme
food mixed with GI secretions
receptive relaxation allows the stomach volume to reach ___L is needed
1.5
receptive relaxation occurs by the ___ reflex pathway, which is stimulated by the ___ of the stomach
vasovagal; distention
what are the 3 parts of the stomach?
fundum, body, antrum
regulated emptying in the stomach is caused by
peristalsis contractions in the antrum push chyme into the duodenum, but most of it is blocked by the pyloric sphincter so it is repulsed and mixed further
gastric emptying requires what 2 things?
- increased peristalsis strength in the stomach
2. relaxation of the pyloric sphincter
increased peristalsis strength in the stomach occurs mainly via inhibitory signals from the duodenum : (5)
- distention
- irritation
- chyme acidity
- chyme osmolarity
- protein breakdown products
what are the 4 pathways for inhibitory signals of the duodenum to increase peristaltic strength in the stomach?
- enteric NS
- inhibitory SNS
- vagus nerve (PNS)
- hormones: CCK and GIP
the max frequency of slow waves in segmentation if ___waves / per
12
what are the 3 ways segmentation increases digestion and absorption??
- mixing of chyme
- minimal forward movement
- increase contact with the walls f the small intestine
in the fed state, peristalsis in the small intestine is ___, having short and slow contractions
weak
in the fed state, it takes ___hr(s) for chyme to pass from the pylorus to the ileocecal valve
3-5
motility of the small intestine id stimulated by the distention of the ___ and __ and by the hormones ___, __ and __
small intestine and stomach; gastrin, CCK, motilin
motility of the small intestine is inhibited by the hormones __
secretin
what type of peristalsis occurs in the fasted state in the small intestine?
migrating motility complex (MMC), where undigested food is moved into the large intestine
what is the function of migrating motility complex in the fasted state>
transport and cleaning
what are the 2 types of movements in the large intestine?
- haustrations
2. mass movements
what are haustrations and their function?
slow (2hr) large circular and longitudinal contractions to increase absorption of water and electrolytes (e.g. Na)
where do haustrations occur in the large intestine/
ascending and transverse colon
what are mass movements and their function?
sustained (10-30 min) peristaltic contractions that transport ,material from the transverse colon towards to rectum
food in the stomach (____) and food in the duodenum (____) can lead to bowel movements
gastrocolic reflex; duodenocolic reflex
give an example of an irritative colon disease
ulcerative colitis
what are the pouches of the large intestine called?
haustrums
