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PHGY 210 > digestion - lecture 4 > Flashcards

digestion - lecture 4 Flashcards

1
Q

describe before meal arrives

A

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

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2
Q

describe when meal arrives

A

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

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3
Q

describe meal in stomach

A

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

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4
Q

describe wave of appropriate activity in upper git

A

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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5
Q

describe distal stomach peristalsis

A

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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6
Q

is there peristalsis in proximal stomach

A

nah

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7
Q

describe gastrointestinal peristalsis

A

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

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8
Q

describe amplitude - gastrointestinal peristalsis

A

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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9
Q

describe frequency - gastrointestinal peristalsis

A

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

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10
Q

describe electrophysiological properties of proximal stomach

A

upper
no peristalsis
steady resting potential
55mv

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11
Q

describe electrophysiological properties of distal stomach

A

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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12
Q

define basic electrical rhythm

A

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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13
Q

describe basic electrical rhythm of distal stomach

A

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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14
Q

describe ber - spikes

A

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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15
Q

when do spikes occur

A

only at peak of depolarization in ber

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16
Q

describe what magnitude of stimulus - spikes does

A

magnitude of stimulus determines number of spikes

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17
Q

describe what number of spikes does

A

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

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18
Q

what is max frequency of muscle contraction in stomach

A

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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19
Q

describe BER

A

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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20
Q

what is icc

A

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

21
Q

what is icc function

A

pacemakers for spontaneous ber of git

22
Q

what do icc cells may play a role in

A

groups of pacemaker cells controlling groups of muscle cells
origin and propagation of ber
communication between nerve and muscle
coordinating groups of muscle cells

23
Q

describe spikes

A

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)

24
Q

describe contractions

A

associated with spikes
amplitude of contractions
maximal f of contractions limited by f of ber
more spikes/burst = bigger contraction

25
Q

describe frequency of contractile activity

A

determined by f of ber

26
Q

describe propagation of contractile activity

A

smooth muscle to propagate electrical signal - spikes from cell to cell
peristaltic contraction requires integrity of ens

27
Q

describe amplitude of contractile activity

A

amplitude determined by magnitude of stimulus stretch ach

28
Q

describe gastrointestinal peristalsis in distal stomach

A

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

29
Q

describe pyloric sphincter

A

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

30
Q

describe the functions of distal stomach

A

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

31
Q

what is meal reduced to

A

semi liquid consistency of chyme

32
Q

how is mixing achieved

A

result of strong antral systole and early closure of pyloric sphincter

33
Q

describe what happens when wave of contraction passes over the antrum

A

some of chyme discharged into duo but most is squirted back into body of stomach at high velocity

34
Q

what results in effective mixing and physical disruption into a suspension of particles <1mm in diameter

A

retropulsive turbulent flow

35
Q

what does propulsion lead to

A

gastric empty
liquids and solids emptied by diff mechanisms

36
Q

describe gastric emptying of liquids - 4

A

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

37
Q

describe gastric emptying of solids

A

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

38
Q

what is distension

A

a factor controlling antral peristalsis

39
Q

what leads to distension and explains

A

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

40
Q

what also controls rate of gastric emptying/antral peristalsis

A

factors in duo

41
Q

what happens if cut vagi to distal stomach

A

sluggish emptying

42
Q

what do factors in duo do

A

slow control of rate of gastric emptying/antral peristalsis

43
Q

name the factors in duo which also control gastric emptying/antral peristalsis

A

distension
ph <3
Osmolarity
chemical composition

44
Q

describe distention - duo factor

A

at level of duo = slow down release since duo doesnt want to be stretch
needs time to break stuff down

45
Q

describe ph - duo factor

A

does not want top be acidic
slow down antral peristalsis

46
Q

describe osmolarity - duo factor

A

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

47
Q

describe chemical composition - duo factor

A

more fat = slower = want meal to move forwards

48
Q

compare gastric vs duodenal factors

A

gastric = increased motility - stretch of stomach, mix and breakdown
duo = decrease motility
push and pull between these 2 factors

PHGY 210 (36 decks)

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