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digestion and metabolism - Wk 3 > small intestine - tuesday > Flashcards

small intestine - tuesday Flashcards

1
Q

What are the two types of contractions that the GI muscle exhibits

A

tonic and phasic

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2
Q

what determines the type of contraction

A

the electrical properties of gut smooth muscle

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3
Q

what type of wave is the tonic contraction

A

long lasting (sphincters/antrum)

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4
Q

what type of wave is phasic contraction

A

slow waves

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5
Q

what can phasic contractions be depending upon ENS/paracrine/endocrine signaling events

A
  • propulsive (peristalsis)
  • mixing (segmentation)
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6
Q

what are the three autonomic innervations of the GI

A
  1. parasympathetic
  2. sympathetic
  3. enteric
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7
Q

what does parasympathetic innervation do to the GI

A

promotes passage of food through GI

rest and digest

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8
Q

parasympathetic innervation to the upper GI is via which nerve

A

vagus nerve

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9
Q

parasympathetic innervation to the lower GI is via which nerve

A

pelvic nerve

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10
Q

what does sympathetic innervation do to the GI

A

inhibits passage of food through GI via:
*closing of sphincters
*inhibition of enteric motor neurons

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11
Q

what nerves does sympathetic innervation to the GI arise from

A

splanchnic nerves

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12
Q

what is the function of the the enteric nervous systen

A

control GI movements, secretions, regional blood flow, fluid flow, etc.

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13
Q

what is the activity of the ENS modulated by

A

the sympathetic and parasympathetic nervous system, but the ENS is able to function without any external input

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14
Q

what two plexuses does the ENS house along its length

A
  • outer plexus: myenteric
  • inner plexus: submucosal
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15
Q

where does the myenteric plexus lie

A

between the inner circular and outer longitudinal layers of the muscularis externa

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16
Q

what does the myenteric plexus control

A

controls the overall muscle tone of the gut as well as its rhythmic contractions

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17
Q

what is peristalsis

A
  • stimulated by distension of the gut
  • inner circular layer of ME forms a contractile ring - squeezing, around the gut
  • outer longitudinal layer contracts - pushing bolus caudally
  • at same time, the distal gut relaxes allowing food to enter
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18
Q

where does the submucosal plexus lie

A

within the submucosal layer

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19
Q

what does the submucosal plexus oversee

A

localized secretions and absorptions of the epithelium in the lumen, regulation of blood flow, etc

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20
Q

what is the submucosal plexus responsible for

A

localized contractions of the muscularis mucosae and the villi of the gut

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21
Q

what are the interstitial cells of cajal the origin of

A

electrical slow waves: sweeping waves of partial membrane depolarization (due to calcium flux)

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22
Q

what do the interstitial cells of cajal serve as

A

pacemaker cells

23
Q

what do interstitial cells of cajal form

A

a network surrounding smooth and longitudinal muscle

24
Q

how are interstitial cells of cajal coupled to smooth muscle cells

A

via gap junctions

25
Q

what are interstitial cells of cajal affected by

A

ENS

26
Q

slow waves initiated by interstitial cells of cajal are necessary but…..

A

not sufficient to induce muscle contraction

27
Q

what happens in the presence of norepinephrine to the slow wave

A

slow wave baseline is lowered, thus raising the threshold requisite for action potential

28
Q

what happens in the presence of acetylecholine to the slow wave

A

the slow wave baseline is raise, enabling the crest to reach the critical point of depolarization

29
Q

action potentials can trigger two major movements..

A
  1. segmentation
  2. peristalsis
30
Q

what is the principal motor pattern

A

segmentation

31
Q

what is segmentation/what does it do

A
  • mix and circulates chyme
  • regional gradient in frequency
32
Q

what is the stimulus and what does it require

A
  • distension
  • requires a preprogrammed ENS
33
Q

what is duration a function of

A
  • nutrient content
  • caloric density of the meal
34
Q

what is short distances of movements

A

peristalsis

35
Q

what is GI emptying

A
  • exit rate from stomach much match digestion rate in SI
  • liquids empty before solids
36
Q

what period foes undigestible food empty

A

interdigestive period NOT the digestive period

37
Q

coordination of stomach emptying with SI digestion occurs via the action of the ….

A

enterogastric reflex

38
Q

ingesta that cannot be broken down into small enough particles remains in the stomach throughout the digestive period. these items are cleared during the interdigestive period by the ….

A

interdigestive (migrating) motility complex

not interdigestive in ruminants, where it’s related to feeding

39
Q

how is the migratory motility complex characterized

A

by stong peristaltic contractions (~ hourly) through the distal stomach while the pyloric sphincter is relaxed

40
Q

what will disrupt the activity of the interdigestive motility complex (in monogastrics)

A

feeding

41
Q

digestive period motility

A
  • nonpropulsive segmentation
  • propulsive peristalsis over short distances
42
Q

interdigestive motility

A
  • strong peristaltic waves over long distances (migratory motility complex)
  • may be involved in aboral localization of gut flora (bacterial conc. high in colon, low orally)
43
Q

bicarbonate secreted by digestive glands must be ____ to maintain pH balance

A

recovered

44
Q

K+ is primarily absorbed by ____ diffusion through a paracellular route

A

passive

45
Q

why is all intestinal H2O absorption passive

A

because the absorption of osmotically active solutes

46
Q

what are the 3 mechanisms of Na+ absorption

A
  • co-transport (SI - jejunum)
  • coupled sodium-chloride absorption (ileum/colon)
  • diffusion
47
Q

what are the 4 steps in the coupled sodium-chloride absortion mechanism of Na+ absorption

A
  1. HCO3 and H+ from H2CO3 via carbonic anhydrase go into lumen
  2. hydrogen exchanged for sodium
  3. accumulating bicarbonate exchnaged for Cl
  4. pumped out by Na/K- ATPase pump
48
Q

what are 3 mechanisms of Cl- absorption

A
  1. coupled sodium-chloride absorption (ileum/colon)
  2. paracellular chloride absorption (SI)
  3. chloride-bicarbonate exchange
49
Q

what happens during coupled sodium-chloride absorption

Cl- absorption

A

Cl accumulation from Cl/Na couple absorption diffuses out once favorable gradient is reached

50
Q

what happens during paracellular chloride absorption

Cl- absorption

A

Cl slips though tight junctions to achieve electrical neutrality after Na cotransport

51
Q

what happens during chloride-bicarbonate exchange

Cl- absorption

A

the Cl-/HCO3- exchanger (or antiporter) to neutralize acid in lumen (colon of ruminants post-fermentation)

52
Q

what is the purpose of bicarbonate recovery

A

to maintain body acid-base balance

53
Q

what are the 4 steps in bicarbonate recovery

A
  1. H+ and HCO3 are formed inside the cell from water and CO2
  2. H+ and Na+ are exchanged at apical membrane
  3. luminal H+ neuralizes HCO3
  4. intracellular HCO3 and Na+ are electrically balanced
54
Q

what is the net effect ofr bicarbonate recovery

A

absorption of sodium bicarbonate NaHCO3

digestion and metabolism - Wk 3 (5 decks)

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