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GI > Gastric Secretion > Flashcards

Gastric Secretion Flashcards

1
Q

What is the function of the fundus?

A

storage

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2
Q

Functions of the body of the stomach?

A

Storage

Produce and Secrete - mucous, gastric acid, pepsinogen, intrinsic factor

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3
Q

Functions of the antrum of the stomach?

A

Mixing/ginding

Release gastrin

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4
Q

Describe the anatomy of a gastric gland

A

Gastric pit is up the way, comprised of surface mucous cells

Gastric gland is below, composed of mucous neck cells, parietal cells and chief cells

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5
Q

What do chief cells secrete? Parietal cells?

A

Chief cells secrete pepsinogens

Parietal cells secrete gastric acid and intrinsic factor

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6
Q

Describe production of HCL in parietal cells of stomach

A

H2O and CO2 combine to carbonic acid (H2CO3) via the enzyme carbonic anhydrase
H2CO3 almost immediately dissociates to HCO3 and H
HCO3 out across basolateral membrane, switched for Cl by transporter
Cl into lumen via leaky channels
H into lumen via H/K exchanger
H2O spontaneously follows H + Cl due to osmotic gradient, hydrochloric acid forms in lumen of stomach

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7
Q

Effect of gastrin on parietal cells?

A

interacts with receptors on basolateral membrane, causes influx of Ca into the cell
Ca activates protein kinases that increase H/K pump activity (HCL production)

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8
Q

Effect of histamine on parietal cells? What type of hormone is it?

A

Paracrine hormone - released locally
Interacts with G-coupled histamine receptors on basolateral membrane - causes cAMP release - protein kinases - increased H/K pump activity

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9
Q

Effect of acetylcholine on parietal cells?

A

ACh released by parasympathetic system, binds muscarinic receptors - influx of Ca into cells
Increases H/K pump activity via protein kinases

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10
Q

Effect of prostaglandins on parietal cells?

A

Exogenous prostaglandins inhibit gastric acid secretion

Stimulate mucous and bicarbonate secretion

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11
Q

3 Mechanisms of promoting gastric acid secretion?

A

Neurocrine - vagus/local reflexes
Paracrine - histamine (ECL cells)
Endocrine - gastrin (G cells)

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12
Q

Where is gastrin released from?

A

G cells in the antrum of the stomach, duodenum and pancreas

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13
Q

Where is histamine released from?

A

ECL cells in the gastric mucosa

enterochromaffin-like cells

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14
Q

What stimulates the release of ACh and gastrin?

A

The sight, smell or taste of food increases vagal output causing ACh/gastrin release

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15
Q

What stimulates ECL cells to release histamine?

A

Gastrin and ACh

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16
Q

What stimuli cause a reduction in gastric acid secretion?

A

Stopping eating - reduces vagal activity
Drop in pH of stomach lumen - reduces gastrin activity
Secretin being released from duodenum

17
Q

How does the small intestine inhibit gastric acid secretion

A

Acid in duodenum stimulates enterogastric reflex and secretin release (secretin stimulates secretion by liver and pancreas)
Fat/carbs in duodenum causes decrease in gastrin and gastric acid secretion via GIP (hormone) release

18
Q

What is the enterogastric (splanchnic) reflex?

A

Reflex in response to a pH of 3-4 in the duodenum, inhibits the release of gastrin by G cells - inhibits gastric secretion

19
Q

What are enterogastrones?

A

Hormones released from glands in duodenal mucosa
Secretin, cholecystokinin (CCK) and GIP
Act to reduce acid buildup in duodenum by inhibiting gastric acid secretion and reducing gastric emptying

20
Q

Where is CCK released from? What is its function?

A

Released in duodenum

Functions:

  • Activate secretion of pancreatic enzymes
  • Reduce gastric emptying
  • Promote bile secretion
  • Relax sphincter of Oddi
21
Q

What is a zymogen? Example?

A

It’s an inactive precursor.

Pepsinogen

22
Q

Where is pepsinogen secreted from and what catalyzes it’s conversion to pepsin?

A 
It is secreted from chief cells of the stomach wall
Low pH (<3) converts it to pepsin
23
Q

What causes the inactivation of pepsins?

A

Raises in pH (towards normal ~7)

24
Q

Which cells produce gastric mucus and what is its function?

A

Produced by surface mucus cells and neck mucus cells

Has a cytoprotective role - protects mucosal surface from mechanical injury. Keeps a neutral pH due to bicarbonate presence - protects against acid corrosion

25
Q

What is the only essential (non-compensatable) function of the stomach?

A

Intrinsic factor production by parietal cells

Allows for vit B12 uptake, RBC maturation. If absent - pernicious anaemia

GI (46 decks)

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