physiology 2 > GIT physiology 1 > Flashcards

GIT physiology 1 Flashcards

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1
Q

mechanical digestion

A

mixing waves - gentle, rippling peristaltic movements - creates chyme

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2
Q

chemical digestion

A

different enzymes require different environments
many molecules require stepwise digestion
all require specific conditions

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3
Q

3 types of chemical digestion

A

secreted enzymes
brush border enzymes
cytosolic enzymes

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4
Q

carbohydrases

A

chemically digest carbohydrates

  • pancreatic amylase
  • a-dextrinase, sucrase, lactase, maltase in brush border
  • ends with monosaccharides which can be absorbed
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5
Q

proteases

A

chemically digest proteins

- trypsin, chymotryp[sin, carboxypeptidase, and elastase from pancreas

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6
Q

lipases

A

chemically digest lipids

  • pancreatic lipase most important in triglyceride digestion
  • emulsification by bile salts increases surface area
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7
Q

nucleases

A

chemically digest nucleic acids

  • ribonuclease and deoxyribonuclease in pancreatic juice
  • nucleosides and phosphates in brush border
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8
Q

3 types of movement in the GI tract

A
  • interdigestive clearing
  • squishing
  • peristalsis
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9
Q

interdigestive clearing

A

driven by a pacemaker

rhythm that sweeps the gut clean

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10
Q

squishing

A

stretch driven rhythmic contraction

for mechanically breaking up food

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11
Q

peristalsis

A

local stretch driven propulsion

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12
Q

mechanical aspects of digestion are modulated by

A

ANS/hormones/paracrines

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13
Q

basal electrical rhythm

A

cells opening and closing channels constantly

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14
Q

enteric smooth muscle

A

tonic/phasic

bundles electrically connected via gap junctions contraction stimulated by Ca

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15
Q

tonic/phasic

A

on/off or oscillating

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16
Q

bundles of enteric smooth muscle is connected via

A

gap junctions

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17
Q

contraction of enteric smooth muscle is stimulated by

A

calcium

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18
Q

Ca2+ channels in enteric smooth muscle are

A

slow to open/close

long AP duration/contraction

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19
Q

excitation of smooth muscle

A

lots of things can open smooth muscle Ca channels

  • ANS activity - acetyl choline
  • enteric nervous system activity
  • local chemistry
  • autorhythmicity - some GIT smooth muscle cells are pacemakers
  • hormones, lumocrines
  • stretch
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20
Q

how does stretch excite enteric smooth muscle

A

stretching smooth muscle opens mechanically gated channels;s and causes it tp contract

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21
Q

stretch triggering enteric smooth muscle is called

A

myogenic stretch response

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22
Q

how does ANS open Ca channel;s

A

acetylcholine stimulates Gi tract smooth muscle

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23
Q

autorhymicity

A

some GIT smooth muscle cells are pacemakers

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24
Q

when there is no food to digest

A

phasic pacemaker dominates - continual slow intrinsic electrical activity - basal electrical rhythm

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25
2 types of phasic pacemaker pattern
- slow waves | - spikes
26
when a slow pave passes the threshold
an AP is generated | this is a spike
27
migrating motor complex
rhythmic contraction event passing from cell to cell via gap junctions lasts 90-120 minutes
28
migrating motor complex stops when
feeding/eating occurs
29
migrating motor complex restarts when
resumes automatically when there is no food
30
segmentation and grinding
stretch initiates local rhythmical circular muscle contraction and relaxation
31
when there is food in the gut there is two stimuli
stretch and osmotic stimuli (hyperosmolar)
32
frequency and strength of segmentation and grinding and peristalsis is affected by
PNS - increased | SNS - decreased
33
peristalsis
retrograde circular contraction and anterograde circular relaxation moves
34
2 signals regulating peristalsis
retrograde signal and anterograde signal
35
retrograde signal results in
results in contraction
36
anterograde signal results in
results in relaxation
37
retrograde signal molecule
acetyl choline
38
anterograde signal molecule
NO and ATP
39
during absorption
segmentation and mixing
40
after completion of absorption
peristalsis to move food onto next section of the gut
41
colon motility
a reservoir for the undigested | slow to absorb sodium
42
ileocaecal valve
restricts colon bugs from leaving the colon | prevents back flow
43
increase in ileum pressure
ileocaecal valve opens
44
increase in colon pressure
ileocaecal valve shuts
45
ileocaecal calve opens when
increase in ileum pressure | opens briefly with each peristaltic wave
46
involuntary sphincters are controlled by
myogenic tone and relative pressures
47
three states of pressure control
resting state - closed, inhibits movement between segments relaxation - open, pressure infront of sphincter>after constriction - very closed, pressure after sphincter>>in front, prevents retrograde flow
48
neural control of sphincters
indirect mechanism - excites interneurons - uses NO/ATP, facilitates flow
49
neural control of defamation
parasympathetic stimulation causes internal anal sphincter relaxation external anal sphincter is under voluntary control
50
2 gut nerve plexuses
- submucosal plexus - meissner's | - myenteric plexus - aurbach's
51
submucosal plexus
between the mucosa and circular muscle layer
52
myenteric plexus
between circular and longitudinal muscle layer
53
myenteric plexus controls
GI tract motility - mechanical digestion
54
submucosal plexus controls
coordinates local secretions and local blood flow | chemical digestion
55
intrinsic reflexes
enteric nervous system only | control secretion, peristalsis, local effects
56
extrinsic reflexes
prevertebral ganglia | transmission of long distance signals
57
entero-gastric reflex
acidic duodenum contents promote colonic contractions
58
gastrocolic reflex
stretched stomach increases colon motility causing evacuation - so stomach can empty into duodenum
59
gastro-ileal reflex
stretch stomach causes ileocaecal valve to open
60
long reflexes
uses the CNS vago-vagal reflex pain reflex defecation reflex
61
3 things regulating hormonal control of motility
secretin cholecystokinin motilin
62
motilin
starts migrating motor complex
63
cholecystokinin (CCK) and secretin
produced by duodenum in response to food | once contents have left the stomach - they slow down the stomach to prevent overload of the duodenum
64
secretin produced in response to
acid (food)
65
cholecystokinin is produced in response to
FAs/peptides (food)
66
motilin initiates
interdigestive clearing - promotes migrating motor complex
67
motilin produced by
small intestine M cells
68
motilin is surpassed by
feeding
69
phases of digestion
cephalic phase gastric phase intestinal phase
70
cephalic phase
largely neural control | smell, sight and thought of food
71
gastric phase
neural and hormonal control | food enters stomach
72
intestinal phase
largely hormonal control | begins when food enters small intestine
73
inter digestive phase
when there is no food
74
what does cephalic phase do
reflex from taste buds stimulates vagal centre in the CNS cranial nerves from medulla stimulate secretion from salivary glands, stomach, pancreas vagus also increases motility of stomach, intestine
75
what does gastric phase do
food in the stomach stimulates vago-vagal reflexes and the release of hormones stimulates gastric and pancreatic secretion, priming for digestion hormones further stimulate gastric secretion
76
what does intestinal phase do
food releases stimulatory hormones from the gut mucosa - hormones stimulate secretion of exocrine pancreases, contraction of gallbladder - inhibitory hormones acting on stomach
77
what is excreted during the intestinal phase
HCO3- to nuetralise the acid, enzymes to further digest food, gallbladder delivers bile salts into intestines
78
why is the stomach inhibited during the intestinal phase
to prevent overloading the intestines
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