Phys - motility of GI Flashcards
What lies in between the circular and longitudinal muscle of the muscularis layer?
Myenteric plexus (of aurbach)
What are the functions of the circular and longitudinal muscles?
circular muscles decrease diameter of bowel
longitudinal shortens length of the bowel
What are slow waves?
depolarization and repolarizations of the membrane potential
What determines the frequency of contractions of the GI?
slow waves
What is the difference between tonic and phasic contraction?
tonic contraction maintains a constant level of contraction without regular periods of relaxation
phasic contractions are periodic contractions followed by relaxation
What is the relationship between slow waves, APs and contractions?
the greater the number of APs on top of the slow wave, the larger the contraction
Which neurotrans increases the amplitude of slow waves and number of APs? What decreases it?
ACh; NE
Where are slow waves generated?
interstitial cells of cajal (pacemaker cells)
What are the muscles of mastication innervated by?
motor branch of fifth cranial nerve; trigeminal n
What is mastication controlled by?
nuclei in the brainstem
What are the three phases of swallowing?
oral phase (initiates swallowing)
pharyngeal phase (soft palate pulled upward, UES relaxes, peristaltic wave)
esophageal phase (swallowing reflex; primary and secondary peristalsis)
What is the swallowing reflex controlled by?
the medulla; vagus/glossopharyngeal n carries afferent sensory input to medulla, it gets processed in brainstem nuclei and efferent input goes to the pharynx
what is the difference between primary and secondary peristaltic wave?
primary is a continuation of the pharyngeal peristalsis (medulla)
secondary peristaltic wave happens if the primary wave fails to empty the esophagus (medulla and ENS) its not dependent on the vagus
How does pressure change during swallowing along the esophagus as a food bolus passes through it?
the pressure in the UES is above atm pressure before swallowing and will increased after
the pressure in the thoracic is slightly below atm pressure but will increase with swallowing
the pressure in the diaphragm is closer to atm pressure after swallowing
the pressure in the LES is above atm pressure and will decrease with swallowing
How does pressure in the esophagus change with achalasia
achalasia is a failure of the LES to relax so it will increase LES resting pressure
What causes GERD?
LES relaxes abnormally or weakens
What tests would you order to diagnose achalasia/for dysphagia?
barium swallow and manometric/ esophageal motility
What are the two regions of the body of the stomach?
orad and caudad
What is receptive relaxation?
its a decrease in pressure and increase in volume of the orad region (vagovagal reflex)
How does pressure change in the orad region of the stomach with swallowing?
as the bolus moves from orad to caudad, the pressure increases as contractions increase
How do parasympathetic and sympathetic stimulation regulate gastric contractions?
parasymp - increase AP and force of of contractions, increase in gastrin and motilin
symp- decrease AP and force of contractions, decrease
What increases gastric emptying?
decrease distensibility of the orad
increased force of peristaltic contractions of cauded stomach
decreased tone of pylorus
increased diameter and inhibition of segmenting contractions of the proximal duodenum.
What factors inhibit gastric emptying?
relaxation of orad
decrease force of peristaltic contractions
increased tone of pyloric sphincter
sepgmentation contractions in intestine
What is the entero-gastric reflex?
negative feedback from duodenum will slow down the rate of gastric emptying
What is gastroparesis?
slow emptying of the stomach/paralysis of stomach in absense of mechanical obstruction
What is a common cause of gastroparesis?
diabetes mellitus (20% type 1 diabetics affected)
injury to vagus nerve can also result in it
What are the symptoms of gastroparesis?
nausea, vomiting, early feeling of fullness when eating, weight loss, abdominal bloating, abdominal discomfort
What is the migrating myoelectric complex?
waves of electrical activity (peristaltic contraction) that sweep through the intestines in a regular cycle during fasting
What molecule mediates the MMC?
motilin
What is the main function of segmentation contraction?
mixing the chyme; doesnt propel the food like peristaltic contractions do
How are slow waves different in the intestines?
they need APs for contraction and they have higher frequency
its frequency decreases as it progresses down the SI (duodenum to ileum)
what do IPANs do?
screen pressure in the lumen; serotonin binds the receptors on these neurons and initiate the peristaltic reflex
what is the difference in functions of the myenteric plexus and submucosal plexus in the SI?
myenteric plexus regulates relaxation and contraction
submucosal responds to the lumenal environment
What is the vomiting reflex?
reverse peristaltic contractions; propel out of the mouth
regulated by medulla
What are the events of the vomiting reflex?
- reverse peristalsis in SI
- stomach and pylorus relax
- forced inspiration to increase abdominal pressure
- movement of larynx
- LES relaxation
- glottis closes
- forceful expulsive of gastric
Where are nerve impulses transmitted to in the vomiting reflex?
vagus and sympathetic afferents travel to multiple brain stem nuclei
distention of the ileum causes ___ of the ileocecal sphincter while distention of the colon causes ___ of the sphincter
relaxation; contraction
