Digestion 2: Motility Flashcards
which layer of the muscle is closer to the lumen? what is its function?
circular layer;
decrease diameter of the GI tract
which layer of muscle is further from the lumen? what is it’s function?
longitudinal layer (lies on top of the circular layer); shortens the GI tract
GI motility is generally controlled by…
ENS
Function of motility
1) move food from mouth → anus
2) mixing: helps absorption
3) mechanical breakdown
the smooth muscles that line the GI are innervated by…
ANS (involuntary), which release NT to send AP through the smooth muscle system
distal end of autonomic neurons have ____
varicosities filled with NT
smooth muscles of the GI propagate AP by…
gap junctions
contraction of smooth muscles in the GI. why?
contract as 1 unit;
AP relayed through all interconnected smooth muscles
how might an AP in the GI smooth muscles happen?
slow wave potentials that reach threshold will fire an AP
slow wave potentials
rhythmic depolarization & repolarization of membrane potentials, but doesn’t always reach threshold
force & duration of muscle contractions depend on…
amplitude & frequency of the AP
frequency of AP in the GI depend on…
slow wave potentials
some specialized smooth muscle cells have ____ activity, meaning they generate ____.
pacemaker;
slow wave potentials generators (allow cells beside them to generate slow waves)
smooth muscle cells with pacemaker activity is called…
interstitial cells of Cajal
interstitial cells of Cajal (ICC) are responsible for…
Generating slow wave potentials in normal muscle cells; propagates through gap junctions
amplitude of slow wave potentials generated by ICC as a function of distance
amplitude decreases over time as the waves travel
can smooth muscle cells generate slow wave potential?
no
where are ICCs located?
all regions & layers of the GI tract
- @ interface between nerve fibers & smooth muscle cells
frequency of slow waves depend on…
where they are located
- higher in small intestines
- lower in stomach
difference between pacemaker in GI and in heart
heart: - frequency 80/min (steady) - always reach threshold - nodes ICC: - frequency varies through GI - no nodes (emit slow waves anywhere) - does not always reach threshold
ICC pacemaker activity is not dependent on… BUT…
neural / hormone input;
can be MODULATED by neural & hormone input
PNS effect on ICC pacemaker activity
Depolarize → easier for slow waves reach AP
- almost guaranteed to have AP every time if there is PNS stimulation
SNS effect on ICC pacemaker activity
hyperpolarize → difficult for slow waves to reach AP
- few contractions
- slow waves flatten → no oscillations
what stimulates depolarization of ICC?
- stretch
- PNS
- hormones: cholecystokinin, gastrin
Muscles in GI are influenced by…
- ICC
- ENS
- PNS / SNS
- hormones
main effect of hormones: motility // secretion?
secretion
which hormones increase gut motility?
motilin
which hormones decrease gut motility?
CCK, secretin
mass movement is specific to…
large intestines
__ and __ regulate movement between different regions of the GI
sphincters;
valves
MMC stands for…
migrating motor complex
MMC is specific to…
motility pattern specific to interdigestive state (between meals)
define: MMC
waves of activity that sweep through the intestines in a regular cycle during a fasting state
- trigger peristalsis
- gets rid of indigestible material to anus
MMC begins in the … and goes to…
in the stomach;
small intestines
if particles in stomach are larger than __, they are not allowed to leave
1 mm
function of MMC
- stomach: flushes > 1mm food particles out of stomach
- small intestines: flush bile through
- sweeps up bacteria
disruption of MMC is associated with…
bacteria overgrowth
MMC is coordinated by…
ENS
3 phases of MMC
3) regular contractions of circular muscles
2) irregular contractions
1) no contractions
1 MMC cycle takes about ___ min. It will continue until…
80 - 110;
cycles from stomach to small intestines until there is FOOD in the duodenum (nutrients will not stop MMC)
Material in the stomach will stop MMC at…
the stomach, but MMC will still occur in the small intestine
motilin is secreted by…
M cells in crypts of duodenum & jejunum
which hormone regulates MMC in humans?
motilin
when is motilin secreted?
during interdigestive state
Motilin acts on ___ neurons and ____ cells to regulate (but NOT ____) MMC
myenteric;
smooth muscle;
initiate
DEGLUTITION
process of swallowing
steps of deglutition
1) tongue pushes bolus against soft palate → triggers swallowing reflex & closes nasal cavity
2) upper esophageal sphincter relaxes, epiglottis close to keep material out of lungs
3) food moves down esophagus (peristalsis & gravity), upper esophageal sphincter contracts
voluntary swallowing is initiated by…
- front of tongue pushing against hard palate
- something must be in mouth
___ is inhibited during swallowing
respiration
___ controls involuntary swallowing (at ____)
ANS;
lower esophagus
CNS control of swallowing (voluntary)
food → CN IX, X → swallowing center in medulla/lower pons → CN V, IX, X, XII → movement of tongue
CN IX
glossopharyngeal never
CN X
vagus nerve
CN V
trigemial never
CN XII
hypoglossal nerve
CNS control of swallowing (involuntary)
food in pharynx → CN X → swallowing center → CN V, VII, IX, X, XII
CN VII
facial nerve
involuntary swallowing process
1) food against soft palate → CNS
2) larynx moves forward allowing bolus go down pharynx, epiglottis & trachea closes
3) after bolus enters esophagus, upper esophageal sphincter closes
___ pushes food into esophagus
base of tongue
CNS control of esophagus
food enters the stomach → CN X → swallowing center → CN X → myenteric plexus → peristalsis in esophagus & relaxation of lower esophageal sphincter
peristalsis is stimulated by…
distension
steps of peristalsis
1) contraction of circular muscles behind food
2) contraction of longitudinal muscles ahead of food
3) contraction of circular muscle layer forces food mass forward
PERISTALSIS
cycle of contractions & relaxations of circular muscle & longitudinal muscles
2 types of peristalsis
- primary
2. secondary
primary peristalsis
bolus into pharynx → top of esophaglus
primary peristalsis is driven by…
extension of the esophagus
when does secondary peristalsis occur? When does it stop?
when bolus gets stuck in esophagus / primary peristalsis couldn’t push it down;
until stuck bolus enters the stomach
process of secondary peristalsis
1) triggered by food stuck in esophagus - stretch receptors (local reflex)
2) push bolus down to stomach
secondary peristalsis is controlled by..
medulla oblongata
peristalsis in esophagus is controlled by…
entirely by ENS
purpose of excitatory & inhibitory neurons of the ENS during peristalsis
excitatory: contract muscles behind & around bolus
inhibitory: relax muscles in front of bolus
which NT are responsible for excitatory neurons controlling peristalsis?
ACh, substance P
which NT are responsible for inhibitory neurons controlling peristalsis?
NO, vasoactive intestinal peptide, ATP
what is triggered when gastric contents splash up the esophagus?
peristalsis activated:
- irritants on lining of esophagus activates secondary peristalsis
orad portion of stomach
closer to mouth
receptive relaxation
relaxation of orad portion of stomach to make room for food entering
receptive relaxation is initiated by ___ reflex
vagovagal
vagovagal reflex
Stomach → brain → stomach reflex
1) afferent fibres from stomach → dorsal-vagal complex in medulla
2) efferent muscle fibre → allow stretch to happen
cutting the vagus nerve will stop ___ , but not ___
receptive relaxation;
peristalsis
what happens if there is no receptive relaxation?
no stretch happens when food enters stomach → pain
vagovagal reflex integrates…
dorsal vagal complex
caudad portion
lower portion of stomach
mechanical digestion in the stomach
retropulsion
- peristalsis cause high pressure chyme
- grinds food particles against each other
purpose of segmentation
- move food back and forth, allowing for mixing of chyme with digestive enzymes in small intestines
- more time for absorption
what cells absorb nutrients in the small intestines?
transport epithelial cells
there is higher frequency of segmentation in the ___ portion of the small intestine than the __ portion
proximal;
distal
peristalsis in the small intestines is due to…
change in segmentation frequency at the various regions
which movement pattern does not propel the material forward?
segmentation
Segmentation
localized concentric contractions of circular muscles
*Think: squeeze right fist then left alternating
purpose of ileocecal valve
- control emptying of small intestines → large intestines
- prevent backflow
how to open ileocecal valve? how to close?
open: distension of ileum & gastroileal reflex
close: distension / buildup of chyme in cecum
ileum empties into ___
cecum
gastroileal reflex
presence of food in the stomach cause ileocecal valve to open
mass movement happens at… (specific)
large intestines: transverse colon & some parts of descending colon
Which segment of the large intestines is used as a storage area?
sigmoid colon
dehydration of feces occurs in the … (specific)
transverse colon
gastrocolic reflex
presence of food in the stomach initiates mass movement (to make room for new food coming in)
gastrocolic reflex is controlled by…
ENS
__ stimulates mass movement, while ___ inhibits it
PNS;
SNS
frequency of mass movement
1-3 times / day (after meals)
mass movement
infrequent waves of contraction in the large intestines that move content large distances at a slow rate
process of defecation
1) pressure in rectum → ENS → peristalsis in rectum & relaxation of internal sphincter
2) distension also stimulate PNS → enhance mass movement in descending & sigmoid colon
3) relaxation of external sphincter if appropriate
4) contraction of abs → expulsion of feces
defecation is the result of..
mass movement
what happens when we want to poop but no toilet?
feces move back up sigmoid colon until next mass movement
EMESIS
vomitting
where in the brain is responsible for emesis?
vomiting center in medulla
body responses to emesis goes through which nerves/areas?
- vagus
- spinal nerves
- phrenic nerve
- stomach
emesis: vagus nerve
- enhance salivation (lube)
- relax esophagus & lower esophageal spincter
- contract pylorus (lower stomach)
emesis: spinal nerves
- inspiration (less pressure on esophagus)
- contract abs (pressure)
emesis: phrenic nerve
diaphragm descend
emesis: stomach
reverse peristalsis
