T1 - Motility of the GI tract Flashcards
what are the four layers of the GI tract from the lumen in?
Mucosa, sub mucosa, muscular externa, serosa
what layer of the GI tract is the connective tissue layer?
sub mucosa
what is most motility governed by in the GI tract?
contraction of smooth muscle
what type of contraction are the oesophagus and anal sphincter governed by and what does this allow?
striated muscles contraction allows voluntary control
what are the two interconnected plexi in the gut wall and where are they found
myenteric plexus in the muscular layer and submucosal plexus in the SM layer
what do the two plexi in the gut wall control?
myenteric controls motility and submucosal controls secretion and local blood flow
what is the parasympathetic innervation up to the TV colon?
vagus
what is the parasympathetic innervation after he TV colon?
sacral parasympathetic nerves
where does sympathetic innervation of motility come from?
paravertebral symp ganglia - coeliac, sup mesenteric and inf mesenteric
where do hormones go after they are secreted from entereoendocrine cells?
into the portal circulation
what cells is CCK released from and what does it cause?
released from I cells in SI and inhibits gastric emptying
what cells is motion released from and what does it cause?
released by M cells and causes gastric and intestinal motility
what are slow waves
cycling waves of negative elec potential that get more positive over time
what are spike potentials
take the membrane to threshold and allow contraction to occur
what three things inhibit contraction?
sympathetic ANS (NA), hormones eg CCK and hyper polarisation
what generates basal metabolic rhythm?
slow waves
what type of contraction involves bursts of circular muscle contraction and relaxation?
segmentation - mixing
what type of contraction in valves contraction behind a a bolus and relaxation in front (only aborally)
peristalsis
what plexus is implicated in hirschprungs disease?
myenteric
what type of epithelia line the oesophagus?
stratified squamous
what type of muscle is in the muscle layer of the oesophagus?
striated
where does striated muscle become smooth muscle in the oesophagus?
after the upper oesophageal sphincter
what type of movement occurs in the oes after the junctions of striated and smooth muscle?
slow peristaltic waves
what causes receptive relaxation in the oesophagus?
when the lower sphincter relaxes
what is achalasia?
when the LOS fails to relax so food stays in the oesophagus
what is GORD?
when the LOS loses tone and causes acidic gastric contents in the oesophagus
what area of the stomach has a third oblique muscle in the muscle layer?
body
what is the response in the stomach when a bolus enters?
receptive relaxation and stimulation from the vasovagal reflex
what forces chyme to the duodenum?
powerful peristaltic contractions
what hormone causes gastric emptying?
motion
what hormones prevent gastric emptying?
cck and secretin
what mixes and grinds food in the distal part of the stomach?
antral systole
what three hormones slow chyme movement to the duodenum and therefore increasing digestion (inhibit gastric emptying)
CCK, secretin and GIP
what is dumping syndrome and when does it occur?
rapid entry of the gastric contents to the SI
- occurs after ingestion of a large meal or post gastrectomy
what is gastroparesis and when does it occur?
when the stomach fails to empty
- can be due to impaired vagal stimulation in the stomach due to severe diabetes
what three things increase the surface area of the small intestine?
1) circular folds (pilae circulars)
2) villi projections of mucosa
3) brush border microvilli on epithelial surface
how long does it take digestion and absorption to occur in the SI?
3-5 hours
what predominantly controls motility in the SI?
intrinsic ENS
what is propulsive peristalsis initiated by?
stretch and hormones
how is segmentation for mixing triggered in the SI?
by stretch receptors that trigger myenteric stimulation of muscle contraction in response to chyme
which hormones excite propulsive peristalsis?
gastrin, CCK, insulin, motion, 5HT
which hormones inhibit propulsive peristalsis?
secretin and glucagon
what is the migrating motor complex and what controls it?
- sweeps the contents of the SI into the colon every 90 mins
- peristaltic contractions
- ENS control
what three things can result from disruptions to peristalsis?
- peristaltic rush (rapid sweeping on contents due to mucosal irritation)
- vomiting (reverse peristalsis)
- paralytic ileus (loss of peristalsis following mechanical trauma)
what two roles does the commensal microbiome in the large intestine play?
- helps digestion
- synthesises vitamin B and K
what forms taniae coli?
thickening of longitudinal muscle into three bands
what forms from tonic contraction of tanaie coli?
haustral bulges
what type of movements allow mixing in the LI?
haustral churning and peristalsis (mass movement and slow waves)
what reflex occurs after a meal due to stretching of stomach and duodenal walls?
gastroduodenal colic reflexes
what initiates the defection reflex?
mass movement of faecal matter into an empty rectum
what does faecal matter in the rectum stimulate?
myenteric plexus and psym ANS
what causes the internal anal sphincter to open
involuntary contraction of longitudinal muscle in the the rectum
what allows defacation?
voluntary relaxation of the the external anal sphincter via skeletal muscle motor neuron stimulation
