digestion - lecture 4 Flashcards
describe before meal arrives
relax muscle
hyperpolarized
increase area in proximal region
vagal efferents release nanc
describe when meal arrives
stretch
further stomach relaxation
ens inhibitory local neurons relax musculature more
still need more stomach relaxation
describe meal in stomach
stretch more
vago vagal reflexes
all 3 components needed for receptive relaxation
describe wave of appropriate activity in upper git
1 - generate pressure to transport to pharynx
2 - reflexes protect airways - stretch
3 - relax ues
4 - contract pharyngeal constrictors = gradient of pressure
5 - relax les = so wave of peristalsis can push food into stomach
6 - accommodate through gastric receptive relaxation
describe distal stomach peristalsis
main form of contractile activity in distal stomach
contractions start at midpoint and then more down to end
across antrum
physical disruption and regulated propulsion
is there peristalsis in proximal stomach
nah
describe gastrointestinal peristalsis
propagated wave of contraction results from series of local enteric reflexes in response to local distension
describe amplitude - gastrointestinal peristalsis
amp of contraction
due to magnitude of stimulus = amount of stretch and ach, interaction of neural and hormonal factors, more stretch = larger contraction
describe frequency - gastrointestinal peristalsis
direction and velocity
due to electrical characteristics of smooth muscle
ber anf icc
Oscillatory membrane potential creates
describe electrophysiological properties of proximal stomach
upper
no peristalsis
steady resting potential
55mv
describe electrophysiological properties of distal stomach
lower
Rhythmic waves of partial depolarization
do not cause muscle contraction
does not cross threshold
-55mv –> -45mv almost but not quite
define basic electrical rhythm
ongoing wave of partial depolarization
10-15mv in amplitude
lasting 1-4 seconds
reccuring at regular intervals
in stomach = every 20 seconds = 3/min
describe basic electrical rhythm of distal stomach
occur synchronously along circumference of stomach- same band of musculature
occur with a delay more distally in stomach
synchronously circumferential
migrates down longitudinal axis
does not cause muscle contraction tho
describe ber - spikes
second electrical signal at peak of ber depolarization = spikes
cause muscle contractions
always at peak = contracts now
spikes= second electrical signal = era - electrical response activity
when do spikes occur
only at peak of depolarization in ber
describe what magnitude of stimulus - spikes does
magnitude of stimulus determines number of spikes
describe what number of spikes does
number of spikes determines amplitude of muscle contraction
More spikes = larger muscle contraction
what is max frequency of muscle contraction in stomach
ber in stomach = 3/min
spikes all on ber peaks = stomach contraction would be 3/min
max freq of muscle contraction is 3/min
describe BER
constantly present - not initiative of contractions
propagated from cell to cell
frequency constant for given region
detectable in both longitudinal and circular muscle
origin = non neuronal, not ens pacemakers
what is icc
network of non neuronal non muscular cells located between smooth muscle layers and enteric plexuses
extending in circumferential and longitudinal directions
may act as intermediary between the neurons and the smooth muscle
kinda a modified fibroblast cell
what is icc function
pacemakers for spontaneous ber of git
what do icc cells may play a role in
groups of pacemaker cells controlling groups of muscle cells
origin and propagation of ber
communication between nerve and muscle
coordinating groups of muscle cells
describe spikes
Intermittent = only present when stimulus sufficient
phase locked to ber = at peak always
stimulus = ach and stretch
calcium dependent
found in longitudinal and circular fibers
cell to cell propagation via gap junctions
number of spikes/burst - depends on magnitude of stimulus (more stretch = more spikes)
describe contractions
associated with spikes
amplitude of contractions
maximal f of contractions limited by f of ber
more spikes/burst = bigger contraction
describe frequency of contractile activity
determined by f of ber
describe propagation of contractile activity
smooth muscle to propagate electrical signal - spikes from cell to cell
peristaltic contraction requires integrity of ens
describe amplitude of contractile activity
amplitude determined by magnitude of stimulus stretch ach
describe gastrointestinal peristalsis in distal stomach
weak, moderate and intense as get closer to duo
thicker musculature towards antrum and larger bands of muscles connected
band of contraction sequentially becomes wider and contractions stronger and more rapid as approach pyloric sphincter
antral systole = clamps down and closes antrum of stomach including pyloric sphincter
entire terminal part of stomach = antrum and pyloric sphincter contract synchronously to close pyloric sphincter
describe pyloric sphincter
OPEN ALL THE TIME
anatomically well developed = huge increase in band of circular muscle
functionally insignificant
open at rest, closed by antral peristalsis
very narrow lumen, behaves as filter = 1-2mm diameter, nothing big can pass
describe the functions of distal stomach
mixing and propulsion= as particles bound back from pyloric sphincter = mix with gastric juice and helps breakdown
physical disruption
move contents forwards and stomach contracts at midpoint
what is meal reduced to
semi liquid consistency of chyme
how is mixing achieved
result of strong antral systole and early closure of pyloric sphincter
describe what happens when wave of contraction passes over the antrum
some of chyme discharged into duo but most is squirted back into body of stomach at high velocity
what results in effective mixing and physical disruption into a suspension of particles <1mm in diameter
retropulsive turbulent flow
what does propulsion lead to
gastric empty
liquids and solids emptied by diff mechanisms
describe gastric emptying of liquids - 4
emptying due to delta p between proximal stomach and duodenum = p1>p2
normally have receptive relaxation, so delta p small = fluid flows slowly to duo
vagotomy (lose receptive relaxation) to proximal stomach –> delta p large - v comfy
Vagotomy to distal stomach only = not much change in liquid emptying = since movement of fluids depends on delta p and not peristalsis
describe gastric emptying of solids
meal is stored in the fundic reservoir - proximal stomach
distal stomach functions as an antral pump
pump 3/min x stroke vol – chyme fluidity and amplitude of contraction
distension –> amplitude of contraction
what is distension
a factor controlling antral peristalsis
what leads to distension and explains
stretch of muscle = leads to depolarization
local ens reflex = sense stretch signal excitatory ens neurons to release ach and increase depolarization of muscles and increase contraction
vago vagal reflex = increase ach and contraction to level of stomach
all 3 determine amplitude of contraction of peristaltic wave
what also controls rate of gastric emptying/antral peristalsis
factors in duo
what happens if cut vagi to distal stomach
sluggish emptying
what do factors in duo do
slow control of rate of gastric emptying/antral peristalsis
name the factors in duo which also control gastric emptying/antral peristalsis
distension
ph <3
Osmolarity
chemical composition
describe distention - duo factor
at level of duo = slow down release since duo doesnt want to be stretch
needs time to break stuff down
describe ph - duo factor
does not want top be acidic
slow down antral peristalsis
describe osmolarity - duo factor
slow down if lots of food and nutrients
hormonal = secretin and cck = at level of duo that can slow peristalsis in endocrine fashion
neural feedback here = slows movement of stomach
when stretch stomach = send vagal response that stretch but then activate ens neurons inhibitory
describe chemical composition - duo factor
more fat = slower = want meal to move forwards
compare gastric vs duodenal factors
gastric = increased motility - stretch of stomach, mix and breakdown
duo = decrease motility
push and pull between these 2 factors
