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ZA - GI Medicine > Gastric Secretion > Flashcards

Gastric Secretion Flashcards

1
Q

Function of fundus?

A

Storage

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2
Q

Functions of stomach body?

A

Storage and production of:

  • Mucous
  • Gastric acid (HCl)
  • Pepsinogen
  • Intrinsic factor
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3
Q

What does HCL 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

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5
Q

What is pepsinogen?

A

The inactive version of protease enzyme pepsin

Pepsin is in this form to stop it digesting protein of actual stomach

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6
Q

Function of the antrum?

A

Mixing/grinding

Making gastrin - a hormone that acts on cells in the body to control acid and pepsinogen secretion

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7
Q

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

A

Mucous neck cells - make mucus

Chief cells - make pepsinogens

Parietal cells - make HCL and intrinsic factor

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8
Q

What do parietal cells contain to help in HCL secretion?

A

Receptors for the various chemicals that affect HCl secretion

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9
Q

How is HCL secreted from the epithelium?

A

1) CO2 from blood + water in the epithelial cell froms carbonic acid via carbonic anhydrase enzyme
2) CO2 quickly degrades to bicarbonate and H+
3) Cl- enters the cell swapping with bicarbonate which enetrs the blood
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+

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10
Q

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

A

Alkalisation due to the bicarbonate being pumped into the blood from the stomach epithelium in exchange for Cl- ions.

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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?

A

Stimulatory:

  • Gastrin
  • Histamine
  • Acetylcholine

Inhibitory:
- Prostoglandin

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13
Q

Where do these 4 chemicals act?

A

Bind to receptors on parietal cells in the stomach epithelium

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14
Q

How does Gastrin affect HCl secretion?

A

Gastrin enters circulation and passes through the heart and heads towards stomach

  • Binds to its g-protein coupled receptor on epithelial cell
  • This causes a rise in Ca2+ ions inside the cell
  • This stimulates the H+/K+-ATPase to pump more H+ into the stomach
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15
Q

How does histamine work to increase HCL secretion?

A

Stomach has a unique histamine G-protein coupled receptor

Once bound it is activates adenosine cyclase which converts ATP to cAMP

cAMP acts on its protein kinase A

This causes H+ to be pumped into stomach

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16
Q

How does Ach work?

A

Acts on cholinergic muscarinic m3 receptors

M3 acts on a g-protein that is coupled to the IP3 system

This causes release of Ca2+ which acts on protein kinase C

H+ pumped into stomach

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17
Q

For all the stimulatory systems, what else is pumped and where?

A

K+ is pumped into the cell

18
Q

How does prostaglandin inhibit HCL ?

A

It turns off adenosine cyclase and stops it turning ATP to cAMP

19
Q

By what mechanisms is HCL secretion controlled?

A

Neurocrine
Endocrine
Paracrine

20
Q

Describe what neuro responses exist.

A

Vagal and local reflexes

21
Q

Desc. what endocrine responses exist.

A

Gastrin response

22
Q

What paracrine response exists? What does paracrine mean?

A

Histamine

paracrine means locally released

23
Q

What is the cephalic phase of gastric acid secretion?

A

Vagus nerve stimulation that occurs before food even reaches stomach

Vagus nerve stimulates release of Ach and g cells which activate gastrin - all these go on to activate parietal cells

Presence of gastrin and Ach causes local release of histamine

24
Q

How can we stop the H+ ion pumps?

A

Proton pump inhibitors - omeprazole

25
Q

Describe the gastric phase of HCL secretion.

A

Stomach distends due to food which activates vagal/enteric reflexes further

  • Ach released
  • Presence of peptides in stomach causes G-cells and gastrin release
  • Gastrin and Ach cause histamine release
26
Q

What inhibits HCL secretion in the cephalic phase?

A

Reduced vagal stimulation

27
Q

What reduces HCL in the gastric phase?

A

A decreased ph due to high levels of HCL = lowered gastrin secretion

28
Q

What inhibits HCL production once food enters the intestinal phase?

A

If acid covered food is detected in the duodenum the enterogastric/splanchnic reflex activates the secretion of secretin

Secretin reduces stimulation of gastrin and also reduces gastrins effect on parietal cells

29
Q

How can fat in the duodenum inhibit HCL secretions?

A

Causes release of GIP which inhibits G-cells

30
Q

Why is acid in the duodenum such a bad thing?

A

Pancreatic enzymes can’t work in acidic conditions

31
Q

What are enterogastrones?

A

Hormones released by gland cells in the duodenal mucosa in response to acid/food

  • Secretin
  • CCK
  • GIP
32
Q

How does secretic, cholecystokinin (CCK) and GIP work?

A

Inhibit gastric acid secretion and reduce gastric emptying by contracting pyloric sphincter

This is all to stop acid in duodenum

33
Q

What secretes pepsinogen?

A

Chief cells

34
Q

What is a zymogen enzyme?

A

An inactive precursor of the enzyme

35
Q

What converts pepsinogen to pepsin?

A

A low pH acts on pensinogenvia acid hydrolysis

36
Q

What happens to the cleaved off zymogen part of the enzyme?

A

Is digested by pepsin

37
Q

What stops pepsin?

A

When all food is digested and HCL is stopped being secreted - pepsin will inactivate at neutral pH

38
Q

What makes gastric mucus?

A

Surface epithelial cells

Mucous neck cells

39
Q

Gastric mucus role?

A

Protects wall against mechanical injury, acid corrosion or pepsin digestion

40
Q

What does mucus have to help it protect?

A

High bicarbonate

41
Q

What is the only essential/non-compensatory role of stomach?

A

Production of intrinsic factor from parietal cells

-needed for B12 absorption

ZA - GI Medicine (16 decks)

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