14 Smooth Muscle and the ENS

Question 1

What is the distribution of smooth and skeletal muscle through the GIT?

Answer 1

smooth throughout

skeletal in pharynx, top third of oesophagus, external anal sphincter

Question 2

What are the 2 types of smooth muscle?

Answer 2

Phasic, for the length of the GIT

Tonic, for sphincters

Question 3

What are ICC’s?

Answer 3

Interstitial Cells of Cajal, the mediators between the ENS and smooth muscle

Question 4

What effects do parasympathetics and sympathetics have on gut motility?

Answer 4

para - stimulates gut motility

symp - inhibits gut motility (stimulates sphincter contraction)

Question 5

Why might Ca2+ not have too much of an effect on smooth muscle contraction?

Answer 5

Because calcium mediates smooth muscle contraction through calmodulin and myosin

Question 6

How does the smooth muscle cell regulate intracellular Ca levels?

Answer 6

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

Question 7

What would activation of the myenteric plexus cause?

Answer 7

increased tonic contraction

Question 8

What would activation of the submucosal plexus cause?

Answer 8

increase secretory activity

Question 9

What are chemoreceptors stimulated by?

Answer 9

low pH
short chain fatty acids
basolateral 5-HT on entero-chromaffin cells

Question 10

What is Hirschprung’s disease?

Answer 10

arrest of craniocaudal migration of vagal neural crest cells in the hindgut at weeks 5-12 of gestation to form the ENS

Question 11

How is HD classified?

Answer 11

extension of aganglionosis
classical (aganglionic segment does not extend beyond upper sigmoid
long
total

Question 12

What are the effects of HD?

Answer 12

agaonglionic aperistaltic bowel segment prevents propulsion of fecal stream, resulting in megacolon

Question 13

In what two conditions does HD commonly occur?

Answer 13

Downs syndrome

Waardenburg syndrome

Question 14

What 3 methods would you use to evaluate a patient with HD?

Answer 14

plain abdominal radiography
rectal manometry
biopsy

Question 15

What is the pivotal point in the pathogenesis of those with Chaga’s disease?

Answer 15

involvement of the ENS

Question 16

What is a key pictoral characteristic of Achlasia?

Answer 16

bird’s beaking

Question 17

How does Achlasia inhibit movement of food into the stomach?

Answer 17

lack of inhibitory neurones in the LOS, excitatory neurones take over

Question 18

How might you treat someone with Achlasia?

Answer 18

calcium channel blockers
botulinum toxin
surgical myotomy

Question 19

What are the 3 phases of gastric motility?

Answer 19

propulsion
grinding
retropropulsion

Question 20

What are the 3 general phases of digestion?

Answer 20

cephalic
gastric
intestinal

Question 21

What are the features of the cephalic phase?

Answer 21

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

Question 22

With regards to stomach motility, what is the function of the Vagus nerve?

Answer 22

It’s parasympathetic, so we want to stimulate motility, contracts antrum and relaxes pylorus

Question 23

What effects do different stimuli have in the intestinal phase of digestion?

Answer 23

Low pH -> high levels of secretin
High fats -> increase CCK
High amino acids -> increase Gastrin
high carbs -> increased GIP secretion

Question 24

What is the ileogastric reflex?

Answer 24

chyme entering the ileum activate pressure receptors which delay gastric emptying via nerve plexi