Lec 11 GI Motility Flashcards
What plexus is between submucosa and circular muscle layer?
meisseners = mucosal plexu
What plexus is circular and longitudinal muscle layers?
auerbachs = myenteric plexus
What makes up the muscularis propria?
- inner circular
- outer longitudinal
How is the longitudinal muscle layer arranged in the colon?
arrounded in 3 parallel bundles = tenia coli
What cells are located in auerbach’s plexus?
interstitial cells of cajal = pacemaker of the gut
What is the slow wave of GI tract?
- constant background rhythm
- initiated by interstitial cells of Cajal in myenteric plexus
- controls the timing of phasic contractions
What is frequency of slow waves in stomach?
3 per minute
What is frequency of slow waves in duodenum and jejunum?
11-12 per minute
What is frequency of slow waves in distal small bowel?
7-8 per minute
What is frequency of slow waves in colon?
3-6 per minute
What is the spike activity of the stomach?
- contractions of smooth muscle that occur only when slow wave depolarizations reach threshold for AP
- rapid depolarization results in contraction of smooth muscle through release of Ca
What is action of ACh on MMC?
increases = pro motility
What is action of gastrin on MMC?
increases = pro motility
What is action of motilin on MMC?
increases = pro motility
What is action of VIP on MMC?
inhibits = anti-motiliy
What is action of secretin on MMC?
inhibits = anti-motility
What is action of neuropeptide Y on MMC?
inhibits = anti-motility
What are the 2 major types of contractions in the small intestine?
peristalsis = slow proximal to distal movement; from longitudinal smooth muscle
segmentation = major contractile grinding/churning/crushing from circular smooth muscle
What things control peristalsis?
- mediated by ACh
- 5HT plays a big role
- substance P may also add to contraction
- NO mediates distal relaxation
What is function of fundus/body of stomach?
receptive relaxation + reservoir; regulates emptying of liquids
What is function of antrum of stomach?
mixes/grinds; regulates emptying of solids
What is fed motor pattern of small intestine?
slow waves w/ increased number of spike potential to promote mixing/absorption of food; segmental
What is fasting motor pattern of small intestine?
- cyclic migrating motor complex
- keeps intestine swept clean of bacteria/residue
What are the 3 phases of the migrating motor complex (MMC)?
Phase I: 45-60 min, no spike potentials, no contractions
Phase II: lasts 30 min; intermittent spikes + contractions [50% of slow waves associated w/ spikes]
Phase III: 5-15 min; each slow wave has spikes and contractions
What are some common causes of small bowel dysmotility?
neuro: parkinsons, post viral scleroderma DM, hypothyroid opiates visceral neuropathy
What is chronic intestinal pseudo-obstruction?
problem where almost no motility of certain segments of bowel; no physical obstruction but basically is obstructed
What are characteristics of high amplitude propagating contractions [HAPC] of colon?
- have amplitude > 100 mmHg
- occur infrequently ~6/day
- function = mass movement
- associated w/ defection
What are characteristics of low amplitude propagating contractions [LAPC] of colon?
- have amplitude < 50 mmHg
- occur > 100/day
- function = transport fluid contents
- associated w/ distension and flatus
What is ogilvie’s syndrome?
non-obstructive colonic dilation
have colonic ieus –> usually due to drugs [narcotics], post op state, electrolyte imbalance, immobility
How do you treat ogilvies?
decompress colon if needed; neostigmine to stimulate parasympathetics
What are criteria for IBS?
recurrent abdominal pain or discomfort with 2 or more of
- improvement with defecation
- change in stool frequency
- change in stool appearance/form
What is treatment for IBS?
- laxative
- anti-diarrheals
- anti-depressants
- serotonin receptor agonists
What is mech behind IBS?
not clear; thought that mech is due to decrease 5HT which is responsible for controlling motility of bowel through enteric nervous system
What things normally determine continence?
- stool volume and consistency
- anal sphincter function
- neurologic integrity
- rectal sensation
- rectal storage capacity
- psychological motivation
most of resting tone of anus depends on what?
internal anal sphincter determines most of resting tone
What are some causes of fecal incontinence?
- back trauma
- sphincter disruption
- medical illness
