motility of the gut Flashcards
is GI muscle single or multi unit smooth muscle ?
coupling of cells to act as single unit
what mechanism operates in smooth muscle to reduce the use of ATP
the latch bridge mechanism
are actin + myosin arrangements highly structured in smooth muscle
no they arent arranged in rows
which cells act as pacemakers in GI tract ?
interstitial cells of Cajal
what is the term used to describe smooth muscle when it is able to function over a wide range of lengths
plasticity
what effects do the following have on gastric motility ? vagal stimulation CCK GIP Secretin
increase
decrease
decrease
decrease
which has the fastest rate of spontaneous activity stomach duodenum ileum colon
duodenum - 13 contractions per minute
what are the functions of motility in the GI tract
mixing
propulsion
what is motility dependent on ?
smooth muscle
enteric nervous system
autonomic nervous system
hormones
describe the contractile activity of the visceral smooth muscle of Gi tract :
shows rhythmic cycles of activity through pacemaker cells ( interstitial cells of cajal)
describe the contractile activity of peristalsis
waves that move bolus
describe the contractile activity of segmentation
churn + fragment bolus
what are 3 main factors influencing GI tract motility ?
- smooth muscle functional syncytium
- neural control
- hormonal control
what is smooth muscle functional syncytium ?
electrical activity of muscle cells
slow wave of pacemaker potentials
spike potentials that result in contraction
how does neural control influence GI tract motility ?
parasympathetic pathway excites + inhibits motility
sympathetic pathway inhibits effects of motility
what are the 2 distinct areas of motor activity in the stomach ?
proximal
distal
what is the migrating motor complex ?
when indigestible solids that have failed to pass through the pylorus can pass into the small intestine between meals
is a result of motor activity
what is the bodies response to the stomach filing ?
stomach pressure remains constant until around 1l of food ingested due to plasticity of smooth muscles
peristaltic waves move toward pylorus at rate of 3 per minute
basic electrical rhythm initiated by pacemaker cells
where does the most vigorous peristalsis + mixing occur
near the pylorus
what happens to chyme at the pylorus ?
- delivered in small amounts into the duodenum
- or if to big forced backwards into stomach for further mixing
what is gastric emptying regulated by ?
neural enterogastric reflex
hormonal mechanisms
how do mechanisms work to regulate gastric emptying ?
inhibit gastric secretion + duodenum filling
carbohydrate rich chyme quickly moves through duodenum
fat-laden chyme is digested more slowly causing food to remain in stomach for longer
how does secretin help regulate gastric activity ?
stimulates HCO3 secretion
inhibits stomach activity
how does CCK regulate gastric activity ?
stimulates gallbladder contraction + emptying
inhibits stomach activity
how does motilin regulate gastric activity ?
increase gastric motility
increases intestinal motility
how does neuronal control regulate gastric activity ?
short reflexs operating in the enteric nervous system inhibit gastric secretions/ contractions
long reflexes operating via the CNS alter autonomic nerve activity
what is the enteric nervous system ?
intrinsic NS that controls different functions of GI tract
why is the ENS describe as separate from the ANS ?
because it has its own independent reflex activity
what are the 2 types of ganglia in the ENS ?
myenteric ( auerbach)
submucosal (meissner)
where is the myenteric plexuses located ?
inner + outer layers of the muscular external
where the submucosal plexuses located ?
in the submucosa
what do neurons in the ENS respond to ?
mechanical deformation
chemical stimuli
temperature
what do receptors in the duodenum + jejunum sense ?
acidity
osmotic pressure
certain fats
amino acids + peptides
what sympathetic nerves innervate the GI tract ?
coelic
superior + inferior mesenteric
hypogastric plexuses
what parasympathetic nerves innervate the GI tract ?
preganglionic
cholinergic fibres
terminate on ganglion cells in the intramural plexuses
