Motility of the GI tract Flashcards
Why is motility used
preparation of ingested food for digestion and absorption, propelling food from mouth to rectum
Circular muscle function
decreases diameter of the segment
Longitudinal muscle function
decreases the length of the segment
Two types of contractions for motility
phasic and tonic
Phasic contraction process
periodic contractions followed by relaxation
Where do phasic contractions occur
esophagus stomach, small intestine, all tissues involved in mixing and propulsion
Tonic contractions
constant level of contraction without regular relaxation usually under basic conditions
Where do tonic contractions occur?
stomach (orad), lower esophageal, ileocecal, internal anal sphincter
T/F Slow was are unique to the GI smooth muscle
T
What are slow waves
depolarization and repolarization of the membrane potential due to electroconductivity to initiate contraction
T/F Slow waves are the same as action potentials
F- slow waves are NOT action potentials
How does slow wave invoke a action potential
slow wave has to touch the threshold for particular membrane
Tension and slow wave relation
if there is slow wave activity - tension (contraction) will follow
What does tension determine
the strength of the contraction
Normal frequency of slow waves
3-12 waves/min
What changes the frequency of slow waves
where the organ is located
T/F Subthreshold depolarization can not produce contraction
F- subthreshold depolarization can produce weak contraction
What are basal contractions
weak contractions produced by subthreshold depolarization
What happens with there is a greater number of action potentials on top of the slow wave
larger phasic contraction
What increases the amplitude of slow waves?
Stretch, Ach, Parasympathetics
What decreases the amplitude of slow waves?
Norepinephrine, Sympathetics
Decreased amplitude of slow waves _____ the number of action potentials
decreases
Where is Ach released from
Vagus nerve
Increased action potentials is caused by ______ amplitude
increase
Pacemaker for GI smooth muscle
Interstitial cells of Cajal
Where do slow waves originate
Interstitial cells of Cajal
Where are the interstitial cells of Cajal located?
myenteric plexus
How do slow waves travel in ICC to smooth muscle
spontaneously and spread rapidly via gap junctions
Calcium channels and GI system smooth muscle
circular and longitudinal muscle increases permeability to calcium and they are important for contraction
What happens with increase in Ca+ channel to open
bigger contraction
What initiates swallowing?
voluntarily in the mouth
What reflex controls swallowing after the mouth
involuntary reflex
What are the 3 phases of swallowing
- Oral phase (voluntary), - Pharyngeal phase, - Esophageal phase
What happen in oral phase
initiation of swallowing
What happens in the pharyngeal phase
passage of food through pharynx into esophagus
Process during pharyngeal phase
soft palate pulled upward –> epiglottis moves –> UES relaxes –> peristaltic wave of contractions initiated in pharynx –> food propelled through open UES
Which part of the swallowing components is striated muscle
Pharynx and UES
Which part of the swallowing components is smooth muscle
Esophagus and LES and stomach (& rest of GI)
What happens during esophageal phase
passage of food from pharynx to stomach
What controls esophageal phase?
swallowing reflex and ENS
Importance of pharynx in respiration and propelling food
pharynx makes switch from respiration for short time to help propel food and swallow
What swallowing reflex is controlled by the medulla
involuntary
What types of receptors are in the pharynx
somtosensory receptors - mechanoreceptors and chemoreceptors
Swallowing process after stimulation
afferent info end to medulla by vagus and glossopharyngeal nerves –> efferent input to pharynx to swallow
Two types of peristaltic waves
primary and secondary
Primary peristaltic wave
continuation of pharyngeal peristalsis
What controls primary peristaltic wave
swallowing center in the medulla
Secondary peristaltic wave
occurs if primary contraction fails to empty esophagus or when there is gastric reflux into the esophagus
What controls secondary peristaltic wave
swallowing center and ENS
T/F Secondary peristaltic wave needs stimulation from vagus nerve
F- secondary peristaltic waves can occur even without stimulation from vagus nerve
What if vagus nerve is cut?
myenteric plexus becomes excitable enough after several days to cause strong 2ndary peristaltic waves
What state are the sphincters in between swallows?
closed
What state is the esophagus in betweens swallows?
flaccid
Which pressure is higher between swallows?
pressure in upper esophageal sphincter is greater than the pharynx and body of esophagus
What is the pressure like in the thorax
subatmospheric
When is the UES open?
when food bolus going from pharynx to esophagus
When is LES open?
when food bolus going from esophagus to stomach
What pressure change occurs during gastroesophageal reflux?
intra-abdominal pressure increased
When can the intra-abdominal pressure be increased?
pregnancy and obesity
What is the opening of the LES mediated by?
vagal nerve
What are two other substances released by vagus nerve?
vasointestinal peptide (VIP), and nitric oxide (NO)
Function of nitric oxide
involved in relaxation of LES
What happens to pressure of LES after bolus enter stomach?
increase in pressure and LES contracts
Gastroesophageal Reflux disease (GERD)
heartburn/acid indigestion
How does GERD occur?
backwash of acid, pepsin, bile into esophagus
What can cause GERD?
scar tissue in esophagus, barret’s esophagus, asthma, chronic sinus infection
Achalasia
damage to nerves in esophagus preventing it from squeezing food into stomach
Symptoms of achalasia
backflow of food in the throat, chest pain, and weight loss
Extrinsic innervation
ANS
Intrinsic Innervation
myenteric and submucosal plexus
3 layers of muscle in the stomach
circular, longitudinal, oblique
What occurs in the orad region of the stomach
receptive relaxation
Function of receptive relaxation
receive food bolus
What is the receptive relaxation
decrease in pressure and increase in volume of orad region
T/F Receptive relaxation is a vagovagal reflex
T
CCK in orad region
CCK decreases contraction and increase gastric distensibility
What occurs in the caudad region of the stomach
mix, digest, and propel gastric contents
Primary contractive event in caudad region
peristaltic contraction from mid stomach to pylorus
What happens as contractions approach the pylorus
increase both force and velocity
Retrorepulsion
as weight comes down, it closes the pylous so some goes through but most goes back into antrum of stomahc
Parasymp stimulation, gastrin, and motilin during gastric contrations
increase AP and force of contractions
Sympathetic stimulation, secretin, and GIP during gastric contractions
decrease AP and force of contraction
How to increase gastric emptying
- decrease distensibility of orad
- increase force of peristaltic contraction of caudad
- decrease tone of pylorus
- increase diameter and inhibiton of segmenting contractions of proximal duodenum
How long does gastric emptying take
3 hours
Factors that inhibit gastric emptying
- relaxation of orad
- decrease force of peristaltic contraction
- increase tone of pyloric sphincter
- segmentation contractions in intestine
What triggers enterogastric reflexes
intestinal mucosal receptors
What kind of responses does receptor activation trigger
- inhibit gastric emptying, 2. increase gastric distensibility by CCK
Slow gastric emptying causes
ulcer, cancer, eating disorder, vagotomy
S/S of gastric emptying
fullness, loss of appetite, nausea
Gastroparesis
slow emptying of stomach/paralysis of stomach
Cause of Gatroparesis
high blood pressure (diabetes), idiopathic
S/S of gastroparesis
nausea, vomiting, early feeling of fullness, weight loss, abdominal bloating
Migrating myoelectric complexes occur when…
emptying of large undigested particles remaining in stomach
What are migrating myoelectric complexes
periodic bursting peristaltic contractions that occurs during FASTING
What mediates MMC
motilin
What inhibits MMCs
feeding
Motility in small intestine function
mix cyme with digestive enzyme and pancreatic secretions, expose nutrients for absorption, propel unabsorbed chyme along small intestine
Two types of contraction in small intestine
- Segmentation contractions, 2. Peristaltic contractions
Segmentation contractions
mix chyme and expose it to pancreatic enzymes and secretions
no forward movement
Peristaltic contractions
propel chyme toward large intestine through circular muscle contraction and longitudinal muscle relaxation
What controls contraction of the intestine
ICC and smooth muscle cells
What is electrical activity?
Slow wave activity is always present whether contractions are occurring or not
Difference between slow waves in stomach and small intestine
Slow waves in intestine DO NOT initiate contractions in small intestine
What is necessary for muscle contraction in the intestine
spike potentials
What determines frequency of contractions in intestine
slow wave frequency
Where in the small intestine is the frequency of contraction the least?
ileum (toward ileocecal junction)
Frequency of slow waves in duodenum
numerous (12 cycles)
What initiates contraction of small intestine
Ach, Substance P
What initiates inhibitory motor neuron in small intestine
VIP, NO
What does submucosal plexus sense in the small itnestine
environment of the lumen
Neural input to intestine contractions
- peristaltic reflex mediated by ENS
- PNS and SNS inhibit contractions
Serotonin on intestine contractions
stimuates
Prostaglandins on intestine contractions
stimualte
Epinephrine on intestine contractions
inhibit
Gastrin, CCK, insulin on intestine contractions
stimulate
Secretin and glucagon on intestine contractions
inhibit
Where is the vomitting reflex found
medulla
How are impulses sent to brain for vomiting reflex
vagal and sympathetic afferent nerve fibers
Reverse peristalsis for vomiting
relaxation of stomach and pylorus, forced inspiration to increase abdominal pressure, movement of larynx, relaxation of LES, closure of glottis, forceful expulsion of gastric contents
What regulates flow of contents from small intestine to large intestine
ileocecal sphincter relaxing periodically
Longitudinal muscle layers of large intestine
taenia coli
What are the two sphincters of large inestine
internal anal sphincter and external anal sphincter
Cells of internal anal sphincter
smooth muscle
Cells of external anal sphincter
striated muscle
Distinguishing characteristic of large intestine
haustras
ENS (myenteric plexus) of large intestine
beneath taenia, innervate muscle laters
Parasymp of large intestine
Vagus (up to transverse colon), Pelvic nerves (descending to rectum)
Symp of large intestine
superior mesenteric, inferior mesenterix, hypogastric, somatic pudendal
Superior mesenteric location for large intestine
proximal region
Inferior mesenteric location for large intestine
distal region
Hypogastric plexus location for large intestine
distal rectum and anal canal
Somatic pudendal nerve location for large intestine
external anal sphincter
Major excitatory mediators
Ach, Substance P
Major inhibitory mediators
NO, VIP
Mass movements of colon
Moves content of large intestine over long distances and stimulate defecation reflex
Final mass movement
propel fecal content into rectum
What ultimately prevents and controls the defecation reflex
external anal sphincter
What controls rectosphincteric reflex and act of defecation
CNS neurons
What happens if a patient is paraplegic
rectosphincteric reflex results in defecation
Hirschsprung Disease
megacolon
Cause of Hirschsprung Disease
ganglion cells absent from segment of colon
Result of Hirschsprung Disease
low VIP levels, smooth muscle constriction and loss of coordinated movement –> result: colon contents accumulates
Diverticulitis
small sacs of intestinal lining that bulge at weak spots
