digestion - lecture 7 Flashcards

1
Q

name and describe what each cell type in gastric glands in fundus and corpus secrete

A

parietal = intrinsic factor and hcl
chief cells = pepsinogen
mucous neck cell = mucin
surface epi cell = bicarb mucus

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2
Q

does mucin protect git mucosa from acid damage

A

huge layer of mucous

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3
Q

what is gmb

A

gastric mucosal barrier
apical surfaces and tjs = impermeable to hydrogen ions

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4
Q

what is muci bicarb layer

A

bicarb secreted and mucin
absorbed into mucous layers
h+ neutralized = bc bicarb also added to layer
protects acidic ph from getting to cells = like surface epi cells

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5
Q

describe gastric mucosa protection

A

muci bicarb layer
gmb
rapid cell turnover = reepithelization ~ 1 mil new cells = stomach and si

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6
Q

how do ulcers form

A

normal hcl output but weak barrie = aspirin and nsaids and helicobacter pylori contribute to weak barrier
or
normal barrier but excessive hcl output = gastrin producing tumours

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7
Q

describe neural regulation of secretion - cephalic phase

A

ens
excitatory
acts on secretory cells = hcl, mucin, pepsin
when stretch vagal inputs (cephalic)
vagally mediated
also vasodilation = parasym
symp = inhibits secretion and vasoconstricts

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8
Q

describe neural regulation of secretion - gastric phase

A

distension - stretch receptors
reinforced by vagal vagal reflex
affected by secretagogues
gastrin goes to heart and increase hcl output from parietal cells

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9
Q

what are secretagogues

A

aas or partially digested proteins which act on gastrin releasing cells = g cells = leads to release of gastrin

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10
Q

what is gastrin

A

peptide hormone
released by endocrine cells in antrum - g cells

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11
Q

what is gastrin released in response to

A

secretagogues - products of protein digestion
local enteric reflexed = distension in antrum
vagally mediated reflexes = vagovagal

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12
Q

what also happens during cephalic phase

A

vagally mediated release of gastrin also released during cephalic phase
want to be prepared before meal arrives

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13
Q

describe gastrin release

A

self regulating
secretagogues (products of protein breakdown) = act on g cell and inhibit acid release from parietal - somatostatin - neg = g cell stops gastrin = goes to heart = parietal cells (give hcl which activates pepsinogen to pepsin optimal ph)
when ph <2 = g cells sense when stop gastrin
so then ph rise = neg feedback loop

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14
Q

what does low ph do

A

Low pH causes the release of Somatostatin which inhibits the G-cell and the Parietal Cell

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15
Q

describe physiological roles of gastrin

A

stimulates hcl secretion
trophic effect = growth, stimulates production of more parietal cells = increase number

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16
Q

what does gastrin stimulate

A

hcl secretion from parietal cell

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17
Q

when is gastrin released

A

Precedes and accompanies meal
occurs as part of cephalic phase

18
Q

describe pos feedback of gastric secretion

A

release stimulated by stretch in stomach and presence of secretagogues in stomach

19
Q

describe neg feedback of gastric secretion

A

release inhibited by low ph in stomach and by somatostatin

20
Q

describe somatostatin

A

release occurs in presence of low ph in stomach
inhibits gastrin release from g cells
inhibits hcl secretion from parietal cells

21
Q

What Role does Histamine Play in HCl Secretion?

A

lots of histamine present in gastric mucosa
histamine administration elicits large vols of gastric juice with lots of hcl

22
Q

what is common mediator hypothesis

A

gastrin and ach cause histamine release
histamine is final local common chemostimulator of parietal cell
WRONGGGGGGGG

23
Q

describe Regulation of Parietal Cell HCl Secretion

A

PARIETAL cells have receptors for all 3 on surface = ach, gastrin and histamine

24
Q

describe receptor interaction hypothesis

A

separate receptors
interaction among 3 receptors
blockade or stimulation of one receptor, changes properties of one or both of the other 2 receptors
cooperative effect = histamine sensitive to ach and gastrin

25
describe permissive hypothesis
histamine constantly released in gastric mucosa and presented to parietal cells as a tonic background = sensitize them to other stimuli blocking tonic background release of histamine or using h2 receptor antagonists inhibits acid secretion in response to ach and gastrin
26
describe intestinal phase
secretagogues to heart --> enterooxyntin --> gastrin ---> acts on parietal cell and secretes hcl also inhibits gastric secretion neg feedback on secretions = secretin, cck, gip, vip, neurotensin
27
describe motor and secretory activities of stomach
at any moment in time reflect balance between excite and inhibitory influences on muscular and glandular cells in gastric wall
28
describe optimal secretory activity
result of interplay between neural and hormonal mechanisms gastric secretions at any moment in time reflects balance between excite and inhibit
29
describe pre intestinal changes
meal reduced to semi liquid consistency = chyme acidified, osmotic pressure unchanged limited digestion
30
describe pre intestinal changes - enzymes
some polysacc --some salivary amylase pytalin (inactivated in acidic ph of stomach)--> disacc some proteins --gastric pepsin--> polypep lipid --> di and monoglycerides, fatty acids - active at stomach only
31
describe upper intesine functions
chyme neutralization = alkaline secretions osmotic equilibration = will be isotonic by time reaches colon = want nutrients to flow back to systems Digestion continues absorption begins
32
name accessory organs which secrete stuff into si
liver gallbladder pancrease all into duo via common pathway = ampulla of water (sphincter of oddi)
33
describe liver and biliary system
right and left hepatic ducts cystic duct common bile duct ampulla of water pancreatic duct w/ sphincter of oddi
34
describe pancreas
endo and exocrine components
35
describe pancreatic juice - composition
0.5-1.5l/day isotonic main electrolytes = sodium, potassium, chloride, BICARB ph = 7.2-8.2
36
describe pancreatic juice - enzymes
pancreas produces largest and most powerful digestive enzymes enzymes = 3% protein, only breast milk has more proteins than this = amylases, proteases, lipases
37
what is important for absorption
dissac must be converted to monosacc right now = amylase converts poly to disacc
38
describe pancreatic proteases - trypsin
proenzyme -- enteropeptidase - enterokinase --> enzyme trypsinogen --> trypsin by enterokinase in SMALL INTESTINE
39
describe pancreatic proteases
chymotrypsinogen --> chymotrypsin proelastase --> elastase procarboxypeptidase --> carboxypeptidase all BY TRYPSIN ENZYME trypsin inhibitor = also secreted by pancreas = to prevent activation in pancreas
40
where is gastrin released
by g cells in stomach and duo
41
what does proton pump inhibitor do
blocks 90-95% of release of acid from parietal cells
42
what happens if block h2 receptor
ulcer diseases treatment = bc blocks 70% of acid release from parietal used to decrease hcl secretion also h+/k+ atpase blockers