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Bmsc 208 > GI 2 > Flashcards

GI 2 Flashcards

1
Q

What is avoiding autodigesting

A

breaking food down into small enough molecules to be absorbed without digesting the cells of the GI tract

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2
Q

what are 3 challenges of digestive system

A

autodigestion, maintaining mass balance, defense

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3
Q

why is it hard to maintain mass balance

A

we secrete a lot more than we ingest (have to reabsorb most)

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4
Q

what is defense in the digestive system

A

absorbing water and nutrients while preventing bacteria, viruses and other pathogens from entering body

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5
Q

what are defense mechanisms

A

mucus, digestive enzymes, acid and lymphoid tissue

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6
Q

where are 80% of lymphocytes

A

in small intestine

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7
Q

how is water secreted

A

ions are transported from ECF into lumen
created osmotic gradient for water to follow

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8
Q

what secretes digestive enzymes

A
  1. exocrine glands (salivary and pancreas)
  2. epithelial cells in stomach and small int
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9
Q

how does secretion work in epithelial cells

A

proteins synthesized on rough ER and packaged in secretory vesicles until needed

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10
Q

what are mucus secretions

A

viscous glycoprotein (mucins) secretions that protect GI cells and lubricate the contents

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11
Q

what type of cell secretes mucus in stomach and salivary glands

A

mucus cells

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12
Q

what type of cell secretes mucus in intestines

A

goblet cells

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13
Q

what do most fluid secretions facilitate

A

digestion, soften and moisten

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14
Q

in stomach what kind of enzymes are there

A

enzymes preferring acidic conditions

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15
Q

in small intestine what kind of enzymes are there

A

enzymes preferring alkaline conditions

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16
Q

two purposes of motility

A
  1. moves food from mouth to anus
  2. mechanically mixing food breaks it into uniformly small particles
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17
Q

what part of digestive tract is skeletal muscle

A

mouth, pharynx, 1st part of esophagus

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18
Q

what is type of muscle is the digestive tract from 2nd part of esophagus on

A

smooth muscle

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19
Q

what is GI motility determined by

A

properties of smooth muscle and modified chemical/mechanical input from nerves, hormones, and paracrine signals

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20
Q

What type of smooth muscle cells are in digestive tract

A

single unit smooth muscle cells

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21
Q

what are single unit smooth muscle cells

A

gap junction slink them electrically and mechanically meaning uniform contraction

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22
Q

tonic smooth muscle that is usually contracted

A

sphincters
relaxes to allow material to pass

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23
Q

phasic smooth muscle that cycles between contraction and relaxation

A

2/3 esophagus, posterior region of stomach, small, large intestines

24
Q

what are slow waves

A

spontaneous depolarizations in GI smooth muscle

25
Q

what are slow waves modified by

A

chemical input from neurons, hormones, and paracrine signals

26
Q

where do slow waves originate

A

network of cells: interstitial cells of cajal (ICC)
next to myenteric plexus

27
Q

what are the ICC cells

A

modified smooth muscle cells serving as the pacemaker for slow wave activity

28
Q

how does slow waves spread through the smooth muscle

A

gap junctions of adjacent smooth muscle

29
Q

why does stomach have waves 3times/min but small int 12 times/min

A

different regions controlled by different ICC groups

30
Q

what are 3 basic patterns of contraction occurring in the GI bringing different types of movement

A
  1. migrating motor complex (motilin)
  2. peristatic
  3. segmental
31
Q

when does migrating motor complex begin

A

between meals

32
Q

where does migrating motor complex start

A

progressive wave of contraction begins in stomach and passes from section to section, terminating in ileum

33
Q

what are the parts of the migrating motor complex

A

45-60 minutes quiescent
20-30 min of infrequent peristaltic contractions
5-15 mins cycle rapid forceful contractions

34
Q

how long is MMC

A

90-120 mins

35
Q

what does the MMC do

A

sweeps food remnants and bacteria out of the upper GI tract and into large intestine

36
Q

what kind of movement are peristaltic contractions responsible for

A

forward movement (esophagus and less frequently in small int.)

37
Q

what is peristaltic contractions

A

progressive wave of contraction of circular muscle behind a mass (bolus) of food (2-25cm/s)

38
Q

what are segmental contractions responsible for

A

mixing (intestines)

39
Q

what are segmental contractions

A

small segments alternatively contact and relax circular and longitudinal (churns and mixes)

40
Q

what are the regulated functions in the GI system

A

motility and secretion

41
Q

what forms the ENS

A

100-500 million neurons of submucosal and myenteric plexuses

42
Q

what do neurons synapse with to regulate GI function

A

with eachother, smooth muscles, glands and epithelial cells

43
Q

where are short reflexes integrated

A

originate in ENS and carried out entirely within wall of gut

44
Q

where are long reflexes integrated

A

within CNS, some originate outside GI tract but some in ENS

45
Q

what GI peptides alter motility and secretion to regulate GI function

A

hormones, neuropeptides, and cytokines

46
Q

what similarities does the ENS share with CNS

A
  • intrinsic neurons: within GI
  • neurotransmitters (many similar to CNS) and neuromodulators
  • glial support cells
  • diffusion barrier (blood gut barrier)
  • integrating center (can function autonomously)
47
Q

what does myenteric plexus add input

A

motility

48
Q

what does submucosal plexus add input

A

secretion from GI secretory cells

49
Q

what stimuli causes short reflexes from ENS

A

distension, presence of food, osmolarity, acid

50
Q

If a long reflex begins in brain what is it

A

cephalic reflex (feedforward and emotional)

51
Q

what other type of info is sent to CNS

A

Sensory info
ENS receives info from CNS via autonomic nerves

52
Q

what does parasympathetic and sympathetic input do for digestion

A

parasympathetic enhances GI function (vagus) sympathetic inhibits

53
Q

what can GI peptides act as

A

hormones or paracrine signals

54
Q

what do GI peptides do

A

excite or inhibit motility and secretion

55
Q

where are GI peptides secreted

A

secreted into lumen to act on apical membrane receptors or ECF to act on neighbouring cells
- some act outside GI (brain)

56
Q

how many peptides have been identified and how many are hormones

A

over 30
only a handful

57
Q
A

Bmsc 208 (33 decks)

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