14 Smooth Muscle and the ENS Flashcards
What is the distribution of smooth and skeletal muscle through the GIT?
smooth throughout
skeletal in pharynx, top third of oesophagus, external anal sphincter
What are the 2 types of smooth muscle?
Phasic, for the length of the GIT
Tonic, for sphincters
What are ICC’s?
Interstitial Cells of Cajal, the mediators between the ENS and smooth muscle
What effects do parasympathetics and sympathetics have on gut motility?
para - stimulates gut motility
symp - inhibits gut motility (stimulates sphincter contraction)
Why might Ca2+ not have too much of an effect on smooth muscle contraction?
Because calcium mediates smooth muscle contraction through calmodulin and myosin
How does the smooth muscle cell regulate intracellular Ca levels?
can release it by the Na-Ca exchanger or Ca pump in plasma membrane. But, we can just intake it into the sarcoplasmic reticulum (SERCA type A pump) and use it
What would activation of the myenteric plexus cause?
increased tonic contraction
What would activation of the submucosal plexus cause?
increase secretory activity
What are chemoreceptors stimulated by?
low pH
short chain fatty acids
basolateral 5-HT on entero-chromaffin cells
What is Hirschprung’s disease?
arrest of craniocaudal migration of vagal neural crest cells in the hindgut at weeks 5-12 of gestation to form the ENS
How is HD classified?
extension of aganglionosis
classical (aganglionic segment does not extend beyond upper sigmoid
long
total
What are the effects of HD?
agaonglionic aperistaltic bowel segment prevents propulsion of fecal stream, resulting in megacolon
In what two conditions does HD commonly occur?
Downs syndrome
Waardenburg syndrome
What 3 methods would you use to evaluate a patient with HD?
plain abdominal radiography
rectal manometry
biopsy
What is the pivotal point in the pathogenesis of those with Chaga’s disease?
involvement of the ENS
What is a key pictoral characteristic of Achlasia?
bird’s beaking
How does Achlasia inhibit movement of food into the stomach?
lack of inhibitory neurones in the LOS, excitatory neurones take over
How might you treat someone with Achlasia?
calcium channel blockers
botulinum toxin
surgical myotomy
What are the 3 phases of gastric motility?
propulsion
grinding
retropropulsion
What are the 3 general phases of digestion?
cephalic
gastric
intestinal
What are the features of the cephalic phase?
conditioned reflex (sight and smell) unconditioned reflex (taste and chewing) inhibitory phase, the vagus nerve inhibitory neurones relax the stomach enabling it to store stuff
With regards to stomach motility, what is the function of the Vagus nerve?
It’s parasympathetic, so we want to stimulate motility, contracts antrum and relaxes pylorus
What effects do different stimuli have in the intestinal phase of digestion?
Low pH -> high levels of secretin
High fats -> increase CCK
High amino acids -> increase Gastrin
high carbs -> increased GIP secretion
What is the ileogastric reflex?
chyme entering the ileum activate pressure receptors which delay gastric emptying via nerve plexi
