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Y2 AlimenTORY > Gastric Secretion > Flashcards

Gastric Secretion Flashcards

1
Q

Whats the function of the fundus?

A

Storage, its got a lot very stretchy rugae

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2
Q

What are the functions of the stomach body?

A 
- Storage
production of:
- Mucous
- Gastric acid (HCl)
- Pepsinogen
- Intrinsic factor
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3
Q

What does Gastric acid do?

A

Begins protein digestion by acid hydrolysis and sterilizes food.

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4
Q

What can survive gastric acid?

A

Only Heliobacter Pylori can survive stomach acid

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5
Q

How does pepsinogen become pepsin and what does it do?

A

Pepsinogen is activated (converted to pepsin) by gastric acid.
Its a protease.

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6
Q

Whats the function of the antrum of the stomach?

A
  • Mixing an Grinding stomach contents

- Gastrin production

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7
Q

What does gastrin do?

A

Its a peptide hormone that stimulates gastric acid production

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8
Q

What kind of cells are in a gastric gland and what do they produce?

A

Mucous neck cells -> mucous

Chief Cells -> Pepsinogens

Parietal Cells -> HCl & Intrinsic factor (contains receptors for the various chemicals that affect HCl secretion)

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9
Q

How is Gastric acid secreted from the epithelium?

A

1) CO2 from blood + water in the epithelial cell froms carbonic acid
2) degrades to bicarbonate and H+
3) Cl- enters the cell swapping with bicarbonate
4) Cl- exits into the stomach through a Cl- channel
5) the H+ from the carbonic acid is pumped into the stomach in exchange for K+ 1 for 1

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10
Q

How does the blood pH change after a meal and why?

A

Transient alkalisation due to the bicarbonate being pumped into the blood from the stomach epithelium in exchange for Cl- ions.
Part of gastric acid secretion

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11
Q

Does gastric acid secretion happen all the time?

A

No only when eating as its a high energy process

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12
Q

What 4 chemicals control the gastric acid secretion? Which are stimulatory and which are inhibitory?
What cell type do they act on to affect HCl secretion?

A

Stimulatory:

  • Gastrin
  • Histamine
  • Acetylcholine

Inhibitory:
- Prostoglandin

They bind to receptors on parietal cells in the stomach epithelium

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13
Q

How does Gastrin affect HCl secretion in the stomach?

A

Gastrin:

  • > Binds to receptor on epithelial cell
  • > Receptor releases intracellular Ca2+
  • > Ca2+ activates protein kinases
  • > Induces H+K+ATPase initiating HCl secretion
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14
Q

How does histamine affect Gastric acid secretion?

A

The stomach has a unique histamine receptor (H2).

  • > Binds to H2
  • > Activates a g coupled protein (Gs)
  • > Converts ATP to cAMP
  • > Acts on protein Kinase
  • > Stimulates HKATPase
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15
Q

How does acetylcholine affect HCl secretion?

A
  • > Binds to receptor on parietal cell
  • > Secretes intracellular Ca2+
  • > Acts on protein kinase
  • > Induces H+K+ATPase
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16
Q

Which two chemicals follow the same pathway to stimulate gastric acid secretion?

A

Gastrin & Acetylcholine both stimulate secretion of intracellular calcium in turn stimulate protein kinases

17
Q

How does prostoglandin affect Gastric acid secretion?

A
  • > Binds to receptor on parietal cell
  • > activates Gi coupled protein
  • > inhibits AC converting ATP -> cAMP
  • > Basically disabling the histamine pathway
  • > Reduction in protein kinase activty & so gastric acid secretion
18
Q

How are vagal and local reflexes involved in gastric acid secretion?

A

They stimulate or inhibit the release of Acetylcholine, gastrin, histamine and prostoglandins depending on the reflex.

19
Q

What phases are there to stimulating or inhibiting gastric acid secretion?

A
  • Cephalic
  • Gastric
  • Intestinal (purely inhibitory)
20
Q

What occurs during the cephalic phase?

A

The sight/smell/taste of food stimulates the vagus nerve

  • > Increases Ach + acts on G cells to increase Gastrin
  • > Both activate ECL cells which produce histamine
  • > All 3 act on parietal cells to induce HCl secretion

When you stop eating the vagal tone decreases and all this is inhibited

21
Q

Why is the cephalic stage so important to digestion?

A

If it didn’t occur food would hit your stomach acid less and bacteria would multiply and you’d get sick

22
Q

What occurs during the gastric phase to stimulate gastric acid secretion?

A

Stimulatory:
1a) Stomach Distension -> Vagal/ENS reflexes -> Ach secretion

1b) Peptides in the lumen -> G cell activation -> Gastrin secretion
2) Both Gastrin & Ach act on ECL cells to induce histamine secretion
3) All 3 act on parietal cells to induce HCl secretion

23
Q

What occurs in the gastric phase to inhibit HCl secretion?

A

Inhibitory:
The more acid released the lower the pH goes.
Lower pH inhibits gastrin release which lowers HCl secretion & inhibits histamine release from ECL cells

24
Q

What occurs during the intestinal phase?

A

Two processes:

1) Acid in duodenum from stomach
- > Enterogastric (splanchnic) reflex + Secretin release
- > Reflex lowers gastrin secretion and secretin stimulates bicarbonate release

2) Fat in duodenum from stomach
- > GIP released (Gastric inhibitory polypeptide)
- > Lowers gastrin secretion and directly lowers parietal HCl secretion

25
Q

Define enterogastrone?

A

A hormone released by glands in the duodenal mucosa to inhibit forward movement of gastric contents

26
Q

Name 3 enterogastrones

A

Secretin
Cholecystokinin (CCK)
Gastric Inhibitory polypeptide (GIP)

27
Q

What triggers enterogastrone release?

A

A response to acid/fats(& products)/amino acids and a hypertonic solution in the duodenum

28
Q

How do enterogastrones affect the gut?

A

They prevent excess build up of gastric contents (chyme) in the small intestine by:

  • Inhibiting Gastric acid secretion
  • Stimulating bicarbonate secretion to neutralize acid
  • Inhibiting gastric motility & contracting pyloric sphincter to reduce gastric emptying
  • Inducing secretion of pancreatic enzymes to break down chyme
29
Q

Define a zymogen?

A

An inactive precursor to an enzyme, activated by another enzyme

30
Q

Why are digestive enzymes stored as zymogens?

A

To prevent self digestion

31
Q

Where is pepsinogen stored?

A

In chief cells in the gastric glands

32
Q

What triggers pepsinogen release?

A

pepsin release is activated alongisde HCl release by Vagal tone and gastrin

33
Q

What activate pepsinogen to pepsin?

A

In the acidic enviroment of gastric acid pepsinogen can cleave itself then pepsin continues cleaving more pepsin off the pepsinogen chains.

34
Q

How is pepsin inactivated?

A

By a neutral pH, so it stops when acid stops too

35
Q

What makes up the gastric mucous layer and what produces it on the surface of the gastric epithelium?

A

Mucous and bicarbonate

Surface epithelium and mucous neck cells

36
Q

Whats the purpose of the gastric mucous layer?

A

Protecting the mucosa against gastric acid corrosion and pepsin digestion

37
Q

What is the only essential (or non-compensated for) function of the stomach?

A

Intrinsic factor secretoin

38
Q

What cells secrete intrinsic factor?

A

Parietal cells , same as HCl

39
Q

What is intrinsic factor required for?

A

Vitamin B12 absorption. The complex of the 2 is absorbed in the ileum.
An intrinsic factor defect causes pernicious anemia as erythrocytes fail to mature.

Y2 AlimenTORY (38 decks)

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