7: GI Tract Motility Flashcards
Slow waves
Depols and repols of membrane potential in GI smooth muscle
How do slow waves cause contraction
Greater number of APs on top of slow waves creates larger contraction
Three things that increase slow wave amplitude
Ach, parasymps, stretch
Two things that decrease slow wave amplitude
NE, sympathetics
ICCS: Interstitial Cells of Cajal
GI pacemakers that spontaneously generate and propagate slow waves; slow waves spread to smooth muscle via gap junctions
Where are ICCs located?
Myenteric plexus and smooth muscle
Phasic vs tonic contraction
Phasic: periodic contraction and relaxation
Tonic: maintain constant contraction
4 places where tonic contraction occurs
Stomach, lower esophagus, ileocecum, internal anal sphincter
Which cannot occur after a vagotomy, primary or secondary peristaltic waves?
Primary
What controls the involuntary swallowing reflex
Medulla
Involuntary swallowing reflex steps
- Food in pharynx -> sensory input via CN 9 and 10
- Swallowing center in medulla -> brainstem nuclei
- Efferent input to pharynx
Achalasia
Impaired peristalsis and incomplete LES relaxation during swallowing
What causes achalasia?
Decreased ganglion cells in myenteric plexus -> LES stays mostly closed during swallowing
Presentation of achalasia
Regurgitation, heartburn, dysphagia
How to Dx achalasia
Barium swallow study
What causes GERD
Motor abnormalities -> low pressure in LES -> persistent reflux -> inflammation
Secondary causes of GERD
Increase in intra-gastric pressure; after a large meal, pregnancy, heavy lifting, etc.
Complications associated with GERD
GI bleed, esophagitis, scar tissue/strictures, Barrett’s esophagus
Max frequency of peristalsis in caudad stomach
3-5 waves/min
Why is gastric emptying closely regulated
Provide time for digestion and neutralizing gastric H in duodenum
SIBO
Colonic bacterial overabundance that can disturb SI motility -> nausea, anorexia, bloating
Slow gastric emptying sx
Fullness, loss of appetite, nausea, sometimes vomiting
What can cause slow gastric emptying
Gastric ulcer, cancer, eating disorders, vagotomy
Tx for slow gastric emptying
Pyloroplasty, balloon dilation
Gastroparesis
Slow emptying of stomach in absence of mechanical obstruction
What can cause gastroparesis?
DM, injury to vagus nerve
Sx of gastroparesis
N/V, early feeling of fullness, weight loss, abd bloating and discomfort
IPAN stands for?
Intrinsic primary afferent neuron
Slow waves in SI vs stomach
In SI, slow waves dont initiate contractions, they just set max frequency for contractions
Vomiting reflex events
reverse peristalsis in SI -> stomach and pyloric relaxation -> forced inspiration to increase abdominal pressure -> movement of larynx -> LES relaxation -> glottis closes -> forceful expulsion of gastric contents
Regulation at ileocecal junction: distention of ileum vs colon
Ileum distention -> relaxes ileocecal sphincter
Colon distention -> contracts sphincter to prevent backflow
Where is the ENS in the LI?
Concentrated beneath tenia coli
What type of nerve innervates external anal sphincter?
Somatic pudendal nerves
