3 Gastrointestinal Physiology Flashcards
4 main topics we discuss
motility
secretion
digestion
absorption
organs of the GI tract
oral cavity pharynx esophagus stomach small intestine large intestine
what are the two GI muscular layers?
- outer, longitudinal layer (shortens tract)
* inner, circular layer (constricts tract)
what muscular layer is close to lumen?
circular
sphincters are located between?
major compartments
what is similar between cardiac and smooth muscle innervation?
NOT every cell is innervated. They form functional syncytium with gap junctions and ephhaptic conduction
**opposite for skeletal
organelles found in smooth muscle are?
- poorly developed SR
- less organized contractile units
- **lack troponin (use calmodulin instead)
most Ca for smooth muscle comes from? binds to?
comes from ECF
*bins to calmodulin bc smooth muscle lacks troponin
two types of electrical waves?
slow waves
spikes
slow waves are also called?
basal electrical rhythms (BERs)
what are slow waves?
spontaneous oscillations of membrane potential= non-propagated (local) potentials
are slow waves or spikes non-propagated or propagated?
slow waves= NON-propagated
spikes= propagated
slow waves do not result in muscle contraction because?
they don’t usually reach the muscles cell’s threshold for excitation
do slow wave frequency vary? Exs?
YES
- stomach= 3/min
- duodenum= 12/min
spikes are also called?
action potentials
when do action potentials occur?
when threshold is reached= propagated potentials
what are “additional signals” for spikes?
nervous, mechanical, hormonal
what are additional signals for spikes required for? (explain process)
for slow waves to become spikes
(additional signals > BERs reach threshold > AP > contraction > travels down GI in wave-like fashion = propagated potentials
what are the two contraction types?
1) tonic= common in sphincters
2) phasic= more coordinated, but not as rhythmic as cardiac
describe tonic contractions. last how long? purpose? Exs?
- sustained contractions
- last min-hrs
- purpose to prevent forward flow until ready
- sphincters and upper stomach (fundus)
describe phasic contractions. last how long? purpose? Exs?
- rapid contractions -contract and relax FAST
- last seconds
- purpose to mix and move
- esophagus, small intestine, lower stomach (antrum)
what are 4 factors regulating GI muscle contraction?
1) entertic nervous system
2) extrinsic NS
3) stretch
4) hormones
what are the enteric nervous system plexuses? location?
1) myenteric plexus
- – b/w inner long and outer circle muscles
2) sunmucosal plexus
- – closer to absorptive surfaces in Submucosa
myenteric plexus controls?
movement: controls and coordinates motility of the gut
submucosal plexus controls?
secretions of the gut
Myenteric and submuscoal plexuses are also known as?
- myenteric= Auerbach’s plexus
* submucosal= meissner’s plexus
are efferent or afferent fibers found in the plexuses?
both
does the enteric nervous system (myenteric or submucosal plexuses) function dependently or independently of extrinsic NS?
BOTH
*independent OR function in conjunction with autonomic extrinsic NS
for the enteric NS, afferent fibers carry what information?
sensory
- myenteric= pressure
- submucosal= chemical
how do enteric NS fibers communicate?
- interconnect/communicate to activate or inhibit each other
- interconnect/communicate with EXTRINSIC (autonomic) NS
- over 20 neurotransmitters have been identified
what does extrinsic NS mean?
OUTSIDE of the gut
- autonomic
- sym and para
where do the sym and para fibers originate for extrinsic NS?
- Sym= thoracolumbar spinal cord (T5-L2)
* para= originate in vagus and pelvic splanchnic nerves (S2-4)`
How does para and sym affect the GI compared to cardio?
- Sym= slows, inhibits, diminishes GI
- –decreases motility and secretions
- Para= activated, speeds up GI
- – increases motility and secretions
- ***opposite is true for cardiac
what is the affect of stretch on the gut?
increases motility, contractility and secretions
the gut has a ‘reflex arc’, this means?
that the plexuses have afferent and efferent fibers to the gut
what are 4 major hormones that affect gut motility?
1) gastrin
2) GIP
3) CCK
4) secretin
gastric mucosa secrets?
gastrin
gastrin is secreted into?
CIRCULATION** not the lumen
duodenal mucosa secrets what hormones?
GIP
CCK
secretin
GIP stands for?
glucose-dependent insulinotrophic peptide (GIP)
CCK stands for?
cholecystokinin
gastrins affect on GI motility?
increase
GIP, CCK, and secretin on GI motility?
stimulate release of what?
decrease (inhibits stomach)
**release of enzymatic carbonate
protein, stretch, and vagus stimuli cause the release of what hormone?
gastrin
CHO and fat stimuli in SI cause the release of what hormone?
GIP from pancreas
Fat and protein stimuli in SI cause the release of what hormone?
CCK from pancreas
acid stimuli in SI cause the release of what hormone?
secretin
what are the two major functions of the release of duodenal hormones?
1) decrease motility and slows emptying of the stomach into the intestine
2) causes release of particular pancreatic enzymes to break down food
