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Semester 4 > Case 1 - Overview of the gastrointestinal tract > Flashcards

Case 1 - Overview of the gastrointestinal tract Flashcards

1
Q

what is the oral/buccal cavity lined with

A

lined by oral mucosa, a thick stratified squamous epithelium that is resistant to abrasion

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2
Q

what does the mucosa produce

A

defensins to inhibit bacterial growth

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3
Q

what type of teeth appear in the first 6-24 months of life

A

deciduous teeth (n=20) appear within the first months of life

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4
Q

what are the deciduous teeth replaced by

A

gradually replaced in childhood as the permanent teeth erupt (finish by approx age 12)

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5
Q

what is there lots of in saliva

A

IgA

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6
Q

diagram showing the location of the different teeth

A
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7
Q

how many incisors are there and what do they do

A

2 - slice and cut

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8
Q

how many canines are there and what do they do

A

1 - tear and rip

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9
Q

how many premolars are there and what do they do

A

2 - grind and crush

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10
Q

how many molars are there and what do they do

A

3 - grind and crush (mostly grind)

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11
Q

what is the formula used by dentists for each side of the mouth

A

formula used to show the 32 teeth in the mouth - 2 incisors in top left, right, bottom left and right and so on

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12
Q

how much of saliva is water

A

approx 99%

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13
Q

what are the different glands that produce saliva

A

parotid, sub lingual, and sub mandibular

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14
Q

what lipases and amylases are in saliva

A

lingual lipases and alpha amylase

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15
Q

is saliva slightly acidic or alkaline and why

A

slightly acidic (pH 6.75-7) to provide reasonably optimal conditions for enzyme funciton

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16
Q

what act as lubricants in saliva

A

mucoproteins (mucin)

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17
Q

what is the most abundant immunoglobulin in saliva

A

IgA

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18
Q

what are included in saliva for dental repair

A

calcium and phosphate

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19
Q

what is salivation controlled by

A

salivatory nuclei in the medulla and pons in the brainstem

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20
Q

what stimulates the production of saliva with a high water content

A

mechanoreceptors and chemoreceptors in the mouth

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21
Q

what is an important feature about mechanoreceptors

A

they are not food specific - non food objects induce saiation

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22
Q

what can also induce salivation

A

inout from higher brain centres and lower digestive tract

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23
Q

what are the two intrinsic nerve plexuses

A

myenteric nerve plexus
submucosal nerve plexus

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24
Q

features of the ENS

A

the submucosal and myenteric plexuses are not simply nerve fibres from the CNS

they have their own neurones akin to the gut brain

the gut is influenced by the rest of the nervous system, but will function without any input from the brain or spinal cord

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25
Q

what does contraction of the circular smooth muscle do

A

squeezes the gut contents

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26
Q

what does contraction of the longitudinal muscle do

A

shortens that portion of the gut

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27
Q

what cells have ‘pacemaker’ activity and what does this mean/do

A

interstitial cells of Cajal

means that the smooth muscle layers in the gut are spontaneously active

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28
Q

what does loss of the cells of Cajal lead to

A

gut motor dysfunction disorders

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29
Q

how long is the oesophagus

A

25cm

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30
Q

what does the submucosa contain

A

blood vessels, lymphatics, nerves, lymphoid tissue and mucus glands

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31
Q

what is the oesophagus lined with

A

stratified squamous epithelium to resist abrasion

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32
Q

what kind of muscle is found in the oesophagus

A

in the first third (voluntary) it is skeletal muscle

in the last third (involuntary) it is smooth muscle

the middle third is mixed

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33
Q

what is the outer layer mostly made up of

A

adventita

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34
Q

what is the last part beyond the diaphragm covered with

A

serosa

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35
Q

what does the epithelium change to at the gastro-oesophageal junction

A

lining changes from squamous to columnar epithelium (glandular)

36
Q

what happens if there is metaplasia?

A

Barrett’s oesophagus - change of epithelium from stratified squamous to gastric due to repeated damage form gastric reflux - precursor to oesophageal cancer

37
Q

diagram showing peristalsis in the stomach

A
38
Q

where is peristalsis confined to in the stomach

A

the lower part

39
Q

what valve opens and closes here and how is it regulated

A

the pyloric valve opens and closes and is tightly regulated

40
Q

what does the action of peristalsis and the pyloric valve result in

A

vigorous churning of contents and relatively slow gastric emptying

41
Q

what is the rate of gastric emptying controlled to some extent by

A

the caloric value of the contents of the duodenum

42
Q

what forms the numerous longitudinal folds (rugae)

A

thick mucosal and sub mucosal layers

43
Q

what happens after a meal in the small intestine

A

there are small irregular contractions of the small intestine

44
Q

what happens in the inter digestive state

A

the small intestine exhibits the migrating motor complex (MMC), which can take up to 2 hours to pass along the small intestine

45
Q

what is the signal to stop this inter digestive activity

A

ingestion of food, and this can be mimicked by gastrin and by cholecystokinin (CCK) which are released from the stomach and intestine, respectively

46
Q

what is CCK

A

is a potent inhibitor of gastric emptying in response to high caloric value in the duodenum, an example of local integration of activity to meet demand

47
Q

how active is the colon

A

active almost continuously, although increased activity can be elicited by particular stimuli

48
Q

how long is transit time in the colon

A

2-3 days

49
Q

what is the major component in terms of transit time (dehydration and storage)

A

the transverse colon is the major component

50
Q

what do contractions of the circular muscle cause

A

haustra - not like peristalsis

51
Q

what happens as one haustrum fills

A

as one haustrum fills and distends, this induces contractions that push food into the next

52
Q

what is the gastrocolic reflex

A

powerful, propulsive contractions can be elicited by the introduction of food to the stomach

53
Q

what is the function of the stomach

A

mixes food
acts as a reservoir

54
Q

what starts disgestion

A

the stomach - proteins, nucleic acids

55
Q

what is the pH of the stomach and what does this do

A

pH 1-2 and this activates some enzymes

56
Q

what is the only truly essential function of the stomach

A

absorbing vitamin B12 using intrinsic factor

57
Q

what does the stomach absorb

A

alcohol
some water
some vitamin B12

58
Q

what produce gastrin

A

mucous cells and enteroendocrine cells produce gastrin. these are tightly coiled

59
Q

what are the exocrine gastric secretions

A

hydrochloric acid
mucus
pepsinogen
intrinsic factor

60
Q

what are the endocrine secretions

A

gastrin
somatostatin

61
Q

what are the main cells of the stomach

A

goblet cells
mucous cells
parietal cells
chief cells
G cells
D cells

62
Q

what do goblet cells do

A

secrete an alkaline mucus

63
Q

what do mucous cells do

A

secrete mucus and pepsinogens

64
Q

what do parietal cells do

A

secrete gastric acid and intrinsic factor

65
Q

what do chief cells do

A

secrete pepsin and gastric lipase

66
Q

what do G cells produce

A

gastrin

67
Q

what do D cells produce and where are they found

A

found in antrum and produce somatostatin

68
Q

what does hydrochloric acid do

A

acidifies the lumen, produces pepsin from pepsinogen

69
Q

what does mucus do

A

protects mucosal surface being damaged by HCL

70
Q

what does pepsinogen do

A

precursor of pepsin (which acts as an endopeptidase)

71
Q

what does intrinsic factor do

A

important in the absorption of Vit B12 and erythropoeisis

72
Q

what does gastrin do

A

stimulates acid production

73
Q

what does somatostatin do

A

inhibits release of gastrin

74
Q

what stimulates the release of pepsinogen

A

acetylcholine i.e vagal input

75
Q

what controls and stimulates HCL

A

acetylcholine i.e vagal input
gastrin (from G cells)
histamine (from enterochromaffin cells)
other hormones

76
Q

what is gastric acid secretion inhibited by

A

somatostatin (via decreased gastrin release)
secretin (via decreased gastrin secretion)
gastric inhibitory peptide and other enterogastrones (directly on parietal cells)

77
Q

what are the 3 phases of gastric secretion

A

cephalic phase
gastric phase
intestinal phase

78
Q

what is the cephalic stage

A

through smell, sight, taste of food releases ACh, stimulating the parietal cells and also the G cells - vagally mediated, about 40% of gastric acid secretion occurs here

79
Q

what is the gastric phase

A

distension and reflex activation of enteric neurones and vagal outflow stimulate the parietal cells and G cells.

digested proteins in the stomach also stimulate the G cells - about 50% of gastric acid secretion occurs here

80
Q

what is the intestinal phase

A

amino acids present in the bloodstream (products of protein digestion) directly stimulate the parietal cells - about 10% of gastric acid secretions occurs here

81
Q

what is the gastric mechanism for the inhibition of gastric secretion

A

if proteins are present in the stomach, they act as buffers to keep luminal pH>3

as the stomach empties, therefore, the luminal pH falls below 3. D cells release somatostatin to inhibit gastrin release and thereby reduce acid secretion

82
Q

what is the duodenal mechanism of gastric secretion

A

acidification of the duodenal lumen releases secretin, which inhibits gastrin secretion

acidification of the duodenal lumen and the presence of fatty acids and salt in the duodenum release gastric inhibitory peptide, which acts directly on parietal cells to inhibit HCL secretion

83
Q

main GI hormones - where are they produced and their major actions

A
84
Q

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A

ehfbeufb eufun

85
Q
A

Semester 4 (80 decks)

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