12 motility in the GI tract Flashcards
What are the 3 functions of motor activity in the GI tract?
segmental contraction for mixing
peristaltic contractions
reservoir formation (sphincters)
What is MMC?
Migratory Motor Complex, pattern of electrochemical activity in GI smooth muscle for moving undigested material in the fasted state
What are the 4 phases of MMC?
prolonged quiescence (90-120 minutes)
increased AP + contractions
Peak activity
declining activity
What are the 3 main functions of MMC?
morve particles of greater than 2mm diameter
clear small intestine of residual content
prevent colic bacteria from migrating to the ileum
What is FMP?
fed motor pattern, it halts MMC during feeding
What regulates FMP?
ENS
Hormones like motilin, released just before stage 3 MMC
What hormones initiate smooth muscle contraction?
motilin and somatostatin
What initiates smooth muscle relaxation?
vasoactive intestinal peptide
What are the 2 reflexes of the ileum?
ileogastric motility (ileum distension -> gastric relaxation) gastroileal reflex (increased gastric activity causes increases ileal activity)
What separates the ileum and colon?
ileocaecal sphincter
What are teniae coli?
the 3 muscular bands running the length of the colon
What are the haustra?
contractions up the colon forming pouches
What is the function of the proximal colon?
absorption and bacterial fermentation
What is the function of the distal colon?
reservoir / storage
What are the 2 phases of colon motility?
colonic rhythmic phasic contractions
giant migrating contractions
Why do we have colonic rhythmic phasic contracitons?
as contents move up the ascending colon, they become more solid as water is absorbed, so we hence have short and long duration contractions here
How does distension activate colon motility?
indigestable food passes quickly, activating pressure receptors, stimulating contraction via the myenteric plexus
What food prevent contraction?
bran
fruit
veg
Name 4 classifications of laxatives
stimulant laxatives
saline laxatives
emollient laxatives
bulk-forming laxatives
How do stimulant laxatives work?
name one household product containing a simtulatnt laxative
increase motility through chemoreceptor activation and myenteric plexus
castor oil has ricinoleic acid, inhibiting Na+ transport
How do saline laxatives work?
give an example
osmosis
Magnesium sulphate
How do emollient laxatives work?
soften faeces
What are bulk-forming laxatives normally made from?
dietary fibre (bran or methylcellulose)
How does the Parasympathetic nervous system stimulate colon motility?
Vagus nerve - RPC’s in cecum, ascending colon, transverse colon
Pelvic nerves from sacral spinal, stimulates GMC (other distal bits)
What is the intrinsic defecation reflex stimulated by and what mediates it?
rectum distension
myenteric plexus
what is the function of the parasympathetic defecation reflex?
relaxation of internal anal sphincter not really enough to force out shit so it helps
