digestion - lecture 4 Flashcards by Misha Gandhi

describe before meal arrives

relax muscle
hyperpolarized
increase area in proximal region
vagal efferents release nanc

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describe when meal arrives

stretch
further stomach relaxation
ens inhibitory local neurons relax musculature more
still need more stomach relaxation

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describe meal in stomach

stretch more
vago vagal reflexes
all 3 components needed for receptive relaxation

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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

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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

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is there peristalsis in proximal stomach

nah

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describe gastrointestinal peristalsis

propagated wave of contraction results from series of local enteric reflexes in response to local distension

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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

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describe frequency - gastrointestinal peristalsis

direction and velocity
due to electrical characteristics of smooth muscle
ber anf icc
Oscillatory membrane potential creates

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describe electrophysiological properties of proximal stomach

upper
no peristalsis
steady resting potential
55mv

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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

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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

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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

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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

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when do spikes occur

only at peak of depolarization in ber

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describe what magnitude of stimulus - spikes does

magnitude of stimulus determines number of spikes

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describe what number of spikes does

number of spikes determines amplitude of muscle contraction
More spikes = larger muscle contraction

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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

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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

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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