motility of gut Flashcards
Is GI muscle single or multi-unit smooth muscle?
single unit – visceral muscle has gap junctions that couples the cells and act as a single unit
What mechanism operates in smooth muscle to reduce the use of ATP
The latch bridge mechanism]
Which cells act as pacemakers in the GI tract?
Interstitial cells of Cajal]
What effects do the following have on gastric motility:
vagal stimulation, CCK, GIP, secretin
Vagal stimulation [increase]
• CCK [decrease]
• GIP [decrease]
• Secretin [decrease]
Which has the fastest rate of spontaneous activity: stomach, duodenum, ileum or colon?
[duodenum – about 13 contractions per minute]
Which muscle(s) is/are involved in peristalsis
circular and longitudinal smooth muscle
what does motility depend on?
smooth muscle, enteric NS, autonomic NS, hormones
what does peristalsis and segmentation do?
waves that move then churn and fragment bolus
neural factors affecting GI motility
- autonomic and enteric NS
- parasymp (vagus nerve): exitatory fibres (acetylcholine) and inhibitors fibres (VIP, ADP)
- symp: inhibitory fibres (noradrenaline)
hormonal factors affecting GI motility
- endocrine (gastrin, CCK, motile)
- local (paracrine, neurocrine)
response to stomach filling
- stomach pressure constant until 1L of food ingested
- unchanging pressure
- peristaltic waves moving towards pylors at rate of 3 per min
- basal electrical rhythum - interstitial cells of cajal
describe gastric contractile activity
most peristalsis occurs near pylorus
-chyme delivered to duodenum in small amounts (3ml) or forced back into stomach for more mixing
regulation of gastric emptying
-regulated by neural enterogastric reflex and hormonal (enterogastrone) mechanisms
describe emptying of carb and fat rich chyme
- carbohydrate-rich chyme moves through duodenum
- fat-laden chyme digested more slowly - remains in stomach longer
regulation of gastric activity - hormones
- secretin: stimulate HCO3 secretion, inhibit stomach activity
- CCK (cholecystokinin): stimulate gall bladder, contractions and emptying, inhibit stomach activity
- GIP (gastric inhibitory peptide): inhibit gastric contractions
- motilin: increase gastric and intestinal motility
regulation of gastric activity - neuronal
-short reflexes: enteric nervous system. inhibit gastric secretion/contraction
-long reflexes: via CNS, alter autonomic nerve.
increases sympathetic activity, decrease para=decrease contraction
what interconnected plexuses are present?
-2 interconnected plexuses: myenteric, submucosal
stomach muscle layers
longitudinal, circular, oblique muscle
what does secretin do
- stimulate HCO3 secretion
- inhibit stomach activity
what does CCK do
- stimulate gall bladder contraction and emptying
- inhibit stomach activity
what does GIP (gastric inhibitory peptide) do?
inhibit gastric contractions
what does motilin do?
increase gastric motility
increase intestinal motility
what pathways are in the enteric NS and what does it do
- separate division of ANS: contains complete reflex pathways, sensory, motor and interneurones
- regulate GI function independently of CNS
what is VIP and what does it do
Vasoactive intestinal peptide
- Induce smooth muscle relaxation (lower oesophagal sphincter, stomach, gallbladder),
- stimulate secretion of water into pancreatic juice and bile
- cause inhibition of gastric acid secretion and absorption from the intestinal lumen.
until when. is stomach pressure constant
until 1L food ingested
what’s the rate of peristaltic wave movement towards pylorus
3 per min
how much chyme is delivered to the duodenum at a time
3ml
difference in the movement of carbohydrate and fat-rich chyme through the duodenum
- carb: mores quickly
- fat: digested more slowly, remains in stomach for longer
