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Alimentary System > [Physiology] Gastric Secretion > Flashcards

[Physiology] Gastric Secretion Flashcards

1
Q

what is the role of the fundas

A

smooth muscle / thin and stretchy (storage little mixing little chemical material)

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2
Q

what is the role of the stomach body

A

Storage
secrete Mucus
produce HCl
pepsin stored in its inactive precursor Pepsinogen
Intrinsic factor
contrains cells that produce intrinsic factor (vitamin B12)

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3
Q

what is the role of the stomach antrum

A

musculature more powerful more mixing everything till lliquid

secretes GI hormone gastrin from G cells travels all over body and acts on the cells in the body just a few cm away

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4
Q

what is found on the surface of gastric glands

A

mucous secreting cells

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5
Q

what is the gastric pit

A

opening of the gastric gland

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6
Q

what are the three main cell types in gastric glands

A

mucous neck cell, parietal cell and chief cell

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7
Q

mucous neck cells

A

mucous producing

mainly immature surface mucous cells waiting to replace some of the cells that slide off

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8
Q

cheif cells

A

recruit inactive precursors to pepsin (pesinogen) - contain it as an inactive form prior to release

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9
Q

parietal cells

A

slightly odd shape - responsible for secretion of HCl and intrinsic factor

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10
Q

CO2 role in stomach lumen

A

waste product of respiration - goes across membrane into lumen of parietal cell and combines with water to form semi stable compound known as carbonic acid

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11
Q

what does CO2 combining with water to form carbonic acid require

A

catalyst (carbonic anhydrase)

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12
Q

what is the difficulty with carbonic acid

A

very unstable immediately dissociates to give H and a bicarbonate ion

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13
Q

what happens to the hydrogen ion that is produced

A

gets pumped out out apical membrane on hydrogen potassium ATPase

  • uses atp proton pump, needs careful regulation
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14
Q

what happens to the bicarbonate ion that is produced

A

transported across basolateral membrane in exchange for chloride ion into blood

increases blood ph above 7.4

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15
Q

what is the increase in blood ph following meals known as

A

post prandial alkalanisatin

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16
Q

what occurs due to the entry and exit of chlorine and H

A

allows water to join stomach lumen causing it to become very acidic PH<2

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17
Q

what does gastrin produced from g cells and gastric antrum bind to

A

CCKB receptors

when gastrin binds to cckb calcium then acts on protein kinase c and increases actvity of hydrogen potassium atpase

increasing level of hydrogen being pumped onto lumen - lowering the ph

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18
Q

what does histamine act on

A

unique receptor in the stomach H2

H2 receptor is coupled up to an enzyme adenylate cyclase by the stimulatory G protein GS

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19
Q

what is the H2 receptor coupled up to

A

enzyme adenylate cyclase by the stimulatory G protein GS

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20
Q

what happens when histamine binds to Gs receptor

A

activates adenyate cyclase and that converts adenosine triphosphate ATP into cyclic AMP

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21
Q

what does cyclic AMP act on once stimulated by histamine

A

its own protein kinase A which also activates hydrogen potassium ATPase increasing its activity and producing more H into the lumen

22
Q

what do prostaglandins act on

A

receptor E3 which is coupled up to adenocyclase by Gi the inhibitory protein

prevents production of camp

23
Q

what does acetylcholine act on

A

vagus nerve innervates cells and releases acetylcholine which acts on a cholinergic receptor (muscarinic M3)

like a gastrin receptor causes a rise in intracellular calcium following acetylcholine binding to that M3 receptor

activate protein kinase 3
activating hydrogen potassium ATPase

24
Q

what are the three mechanisms gastric acid secretion is controlled by

A

Neurocrine (vagus/local reflexes)
Endocrine (gastrin)
Paracrine (histamine)

25
Q

what stimulates the vagus nerve

A

sight, smell and taste of food

26
Q

what does stimulation of the vagus nerve stimulate

A

ACh (acetylcholine) and G cells (Gastrin) to parietal cells

27
Q

what does gastrin and ACh stimulate

A

ECL cells which produce histamine to parietal cells

28
Q

what does distention / physical presence of food cause

A

vagal/enteric reflexes releasing ACh to parietal cells

29
Q

what do peptides in lumen stimulate

A

g cells which produce gastrin to parietal cells

30
Q

gastrin/ACh

A

ECL cells releasing histamine

31
Q

cephalic phase

A

stopping eating (reduces vagal activity)

32
Q

gastric phase

A

reduces PH and increases HCl
reduces gastrin

33
Q

intestinal phase

A

acid in duodenum

  • enterogastric (splanchnic reflex)
  • secretin release
34
Q

what does the enterogastric (splanchnic reflex) and secretin release cause

A

reduced gastrin secretion and reduced gastrin stimn of parietal cells

35
Q

what does fat/CHO in duodenum cause

A

GIP release

36
Q

GIP release cause

A

Gastrin secrn
Parietal HCl secrn

37
Q

Enterogastrones

A

Hormones released from gland cells in duodenal mucosa - secretin, cholecystokinin (CCK), GIP

38
Q

when are enterogastrones released

A

in response to acid, hypertonic solutions, fatty acids or monoglycerides in duodenum

39
Q

how do entergastrones act

A

Act collectively to prevent further acid build up in duodenum

40
Q

what are the two strategies by which enterogastrones act

A

inhibit gastric acid secretion
reduce gastric emptying (inhibit motility/contract pyloric sphincter)

41
Q

pepsinogen secretion

A

Pepsinogen (zymogen = inactive prcursor) secreted by Chief cells

42
Q

Low pH (<3) → Pepsinogen → Pepsin

A
43
Q

what does zymogen storage do

A

prevents cellular digestion

44
Q

when are pepsins inactivated

A

neutral pH

45
Q

Mechanisms for pepsin control of pepsin secretion parallel HCl secretion

A
46
Q

where is gastric mucous produced from

A

produced by surface epithelial cells and mucus neck cells

47
Q

what role does gastric mucous play

A

Protects mucosal surface from mechanical injury

Neutral pH (HCO3) → Protects against gastric acid corrosion and pepsin digestion due to high bicarbonate content

48
Q

what is intrinsic factor

A

Only essential (non-compensated) function of stomach

Produced by parietal cells

Required for vitamin B12 absorption

49
Q

what happens to intrinsix factor/B12 complex

A

Intrinsic factor/B12 complex absorbed from ileum
taken up to liver where it gets stored - three years worth in liver

50
Q

what defect with intrinsic factor/B12

A

Pernicious Anaemia (failure of erythrocyte maturation)

51
Q
A

Alimentary System (44 decks)

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