GI motility Flashcards
enteric NS regulation of motility
mucosal layer detest chemicals or mechanical forces
receptor cell bodies are in the submucosal (meisnners) plexus
interneurones transmit signals to the myenteric plexus (auerbachs)
effector neurones in auerbachs modulate sensor activities in smooth muscle layers
modulation of enteric with parasym
release ach onto excitatory enteric neurones
increases motility
modulation of enteric with sym
noradrenaline acts on inhibitory enteric neurones (release VIP, NO)
decrease motility
activity in stomach in fed state
- propulsion = propelled by peristalsis towards antrum, initiates pacemaker cells in the greater curvature, slow waves of depolarisation spread and may excite smooth muscle
- mixing in antrum: contents forced towards the antrum
- retropulsion: contraction of pylorus and antrum closes the sphincter, forces larger material back into antrum
effects of continual cycles in stomach
contents become increasingly fluid over time creates chyme ( v. important) more chyme = sphincter open for longer
other important action of stomach
as a storage organ
motility of stomach int he fasted state
MMCs (migrating motor complexes) spread from stomach to small intestine
slow waves of increased depolarisation and then decreases again
sweeps stomach contents into duodenum
motilin initiates in stomach
feeding terminates MMC
motility of small intestine
exhibits slow waves of depolarisation, initiates contraction of circular smooth muscle
waves are a result of transient relief of enteric inhibition, frequency decreases along small intestine
motility of small intestine in fed
isolated contraction of circular muscle causes segmentation or churning
peristalsis causes propulsion, propagate only over short distances
motility of small intestine in fasted
MMC
movement from small to large
ileo-caecal sphincter separates
distension of ileum promotes relaxation
vomiting process
intitiated by vomiting centre in medulla
reverse peristalsis of small intestine, relax pyloric sphincter and stomach
large intestine motility
longitudinal muscle creates taeniae coli that define folds
slow wave depolarisation induces contraction of circular smooth muscle to produce segmentation
waves increase frequency along large intestine
segmental contraction of haustra (folds) produces pendular movements contents
large peristaltic propulsions occur infrequently
distal colon motility
non-propulsive segmentation which retards flow
rectum motility
intermittently receives material and undergoes segmental contraction
distension causes internal sphincter to transiently relax
external sphincter can override this reflex and contract
gall bladder motility controlled by
CCK
stimulates gallbladder smooth muscle contraction and relaxes sphincter of Oddi
allows bile to flow from duct into Pancreas
bile components
bile salts water and electrolytes lecithin cholesterol pigments like bilirubin
secretion of bile stages
- hepatocytes synthesise primary bile acids from cholesterol
- acids are conjugated to glycine or choline, ionise and exist as Na+ or K+ bile salts
- salts actively secreted into lumen by ATPase
formation of secondary bile acids
- result from bacterial deconjugation, dehydroxylation of primary bile salts in the intestine
- some bile acids are reabsorbed in the ileum and returned to the liver bound to albumin
- can be taken back into hepatocytes
- enterohepatic circulation
- bile acids can be recirculated 3x before digestion is complete
conjugated bile acids features
amphiphatic
form mixed micelles in aqueous environment
vehicle for lipid soluble substances int he aqueous environment of small intestine
function of cells lining bile ducts
cholangiocytes
secrete watery NaHCO3, similar to mechanisms in pancreas
secretion stimulated by secretin, glucagon, VIP to increase cAMP and activate CFTR
gall bladder function
stores bile
epithelial cells reabsorb NaCl to concentrate bile
what is H pylori associated with?
peptic ulcers
also has been linked to some cancers
therefore can be treated with chemotherapy
