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Alim 1 > gastric acid secretion - regulation > Flashcards

gastric acid secretion - regulation Flashcards

1
Q

what are the contents of normal gastric juice in the fasting state

A

cations: na, k, mg, h
anions: cl, hpo4, so4
pepsins, lipase
mucus
intrinsic factor

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2
Q

normal pH of fasting gastric juice

A

about 3.0

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3
Q

what are secreted by the fundus and body of the stomach

A

mucus
HCl
pepsinogen
ALL EXOCRINE

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4
Q

what are secreted by the antrum

A

dec HCl

inc gastrin

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5
Q

what are the walls of tubular glands in epithelial cells lined with

A

parietal cells

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6
Q

what do parietal cells secrete

A

HCl and intrinsic factor

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7
Q

What do enterochromaffin-like cells (ECL) secrete

A

paracrine agents eg histamine

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8
Q

how is gastric acid made in the stomach lumen

A

bicarb exhanged for Cl- in the blood - acidity of venous blood from stomach is dec c.f. blood serving it.
excess Cl- diffused into stomach through cl channels; H+ pumped into stomach via K+ATPase
results in net flow of H+ and Cl- out of parietal cell and into lumen

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9
Q

how does mucus protect against H+ secretion

A

inc HCO3 forms water insoluble gel on epithelial surface

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10
Q

effect of lipase on triglycerides

A

converts into fatty acids and triglycerol

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11
Q

what does intrinsic factor do

A

prevents pernicious anemia - absorbs Vit B12

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12
Q

what does HCl do

A

kills bacteria
denatures digested food
activates PEPSINOGEN

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13
Q

What are the phases of HCl secretion by parietal cells

A

cephalic
gastric
intestinal

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14
Q

what regulates HCl secretion

A

neuronal pathways, duodenal hormones

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15
Q

how do neuronal pathways and duodenal hormones regulate secretion of HCL

A
  1. directly, on parietal cell
  2. indirectly influence gastrin and histamine secretion
    BOTH UPREGUALTE ACID SECRETION
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16
Q

how is gastric acid secretion regulation in the cephalic phase

A

ach released
stimulated release of histamine from ECL cells
ach acts directly on parietal cells - inc HCl

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17
Q

how is gastric acid secretion regulated in the gastric phase

A

stomach distension inc pepitde conc

inc acidity/ lowering of [H+]

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18
Q

why is the acidity of the lumen of the stomach higher before a meal

A

no bueffers

19
Q

what do proteins do to luminal acidity

A

act as buffers in the gastric lumen - so HCl secretion increases

20
Q

mechanism for effect of proteins on luminal acidity

A

proteins remove free H+ - their conc decreases; proteins remove inhibitory effect of HCl on gastrin and therefore acid secretion
gastrin-mediated acid secretion is increased

21
Q

summary of gastric phase

A

food in stomach:

  1. distension - neural reflex - ach on parietal cells
  2. buffers acid - blocks stimulation of somatostatin secretion
  3. peptides, AAs, act on G cells for gastrin release
22
Q

what increases gastrin secretion

A

luminal distension, inc activity of PSNS nerves to stomach

23
Q

what inhibits gastrin secretion

A

increased HCl secretion

24
Q

what does gastrin secretion promote

A

histamine secretion, acid secretion from parietal cells

25
Q

what can act on parietal cells to increase acid secretion

A

gastrin, histamine

increased activity of PSNS nerves on stomach

26
Q

function of the intestinal phases of gastric acid secretion

A

balances secretory activity of stomach and digestive/absorptive capacities of the SI

27
Q

how does the high acidity of the duodenal contents affect acid secretion

A

reflexly inhibits it

28
Q

what can inhibit acid secretion

A 
duodenal distension
hypertonic solution
AA
fatty acids
monosaccharides
29
Q

what does inhibition of acid secretion in the SI depend on

A

chyme volume and composition

30
Q

how is acid secretion inhibited in the intestinal phase

A

short and long neuronal reflexes, hormones eg secretin and CCK inhibit parietal cell acid secretion

31
Q

what can lack of HCl result in

A

failure of protein digestion - production of gastric acid in the stomach is absent or low

32
Q

symptoms of HCl deficiency

A

undigested food in stool
flatulence, bloating
lack of intrinsic factor

33
Q

treatment of HCl deficiency

A

bitter herbs
lemon juice, vinegar, vit b1
all stimulate HCl secretion

34
Q

other ways HCl secretion can be stimulated

A 
caffeine
alcohol
nsaids
nicotine
h. pylori
stress
35
Q

effect of histamine on gastric acid secretion

A

inhibition

36
Q

effect of histamine / ach/ gastrin on binding to parietal cells -

A

increased HCl secretion

37
Q

where is pepsin secreted from

A

chief cells as pepsinogen

38
Q

how is pepsinogen activated

A

high [proton] - high acidity exposes its active site

39
Q

how is pepsinogen inactivated

A

entry of food into SI - HCO3 - and peptides neutralise H+

40
Q

what stimulates pepsinogen secretion

A

inputs to chief cells from nerve plexus

stimulators/inhibitors of acid secretion in cephalic and intestinal phases exert the same effect on pepsinogen secretion

41
Q

what does pepsin do

A

initiates protein digestion - degrades proteins in food into peptides

42
Q

pepsin in not required for food digestion, but what is?

A

intrinsic factor - secreted by the parietal cells

43
Q

how do NSAIDS eg aspirin affect acid secretion

A

impair barrier properties of mucosa
supress gastric prostaglandin synthesis - COX inhibtion
inhibit platelet aggregation

Alim 1 (11 decks)

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