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GI - Year 2 > Gastric Secretion > Flashcards

Gastric Secretion Flashcards

1
Q

What is the function of the fundus of the stomach?

A

Storage

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2
Q

What are the functions of the body of the stomach?

A 
Storage
Mucus
HCl (stomach acid)
Pepsinogen
Intrinsic factor
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3
Q

What are the functions of the antrum?

A

Mixing/grinding

Gastric

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4
Q

Why does the stomach not digest itself?

A

Enzymes are stored in inactive precursor forms

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5
Q

What is the content of mucous neck cells?

A

Mucus

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6
Q

What is the content of chief cells?

A

Pepsinogens

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7
Q

What are contents of parietal cells?

A

HCl

Intrinsic factor

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8
Q

What regulates low pH in stomach and higher pH in blood?

A

CO2 combines with water in cytoplasm (carbonic anhydrase present) = H2CO3
H ion pumped out against massive gradient as K moves into cell using ATP hydrolysis
Bicarbonate is exchanged for chloride which moves through cell and out with H ion forming osmotic gradient
Causes pH in stomach to drop = acidic
Bicarbonate in blood causes increase in blood pH

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9
Q

What are the 3 stimulatory signalling substrates involved with gastric secretion?

A

Gastrin
Histamine
Acetylcholine

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10
Q

What is an inhibitory signalling substrate involved with gastric secretion?

A

Prostaglandin

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11
Q

What effect does gastrin have on proton pump?

A

Increases activity

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12
Q

How is cyclase produced?

A

Type II histamine receptors couple with stimulator gene

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13
Q

What type of cells have receptors for gastrin? + effect

A

Parietal cells

Causes rise in intracellular calcium

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14
Q

Where does acetylcholine come from?

A

Vagus and enteric nerves

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15
Q

What happens to acetylcholine when it binds with receptor?

A

Generates into calcium which adds to protein kinases

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16
Q

What effect does prostaglandin have?

A

Prostaglandins couple up with glandin 3 receptors which are bound up to inhibitory gene which prevents ATP turning into cAMP
Affects production of protein kinases = inhibits proton pump

17
Q

What 3 mechanisms control gastric acid secretion?

A

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

18
Q

What happens in the cephalic phase? + result

A

Sight, smell, taste and or thought of food causes stimulatory response -> increase vagus nerve stimulation -> acetylcholine
Increase vagus nerve stimulation also causes G cells to produce gastrin
Gastrin and ACh trigger ECL cells to release histamine
Result = more HCl

19
Q

How is cephalic phase inhibited?

A

By stopping eating which decreases vagal activity

20
Q

What happens in the gastric phase?

A

Distension of stomach causes vagal/enteric reflexes triggers release of ACh
Peptides in lumen causes G cells to release gastric
Gastrin/ACh causes ECL cells to release histamine

21
Q

How is gastric phase inhibited?

A

Decrease in pH (increase in HCl) causes decreased gastrin

22
Q

How is intestinal phase inhibited?

A

Acid in the duodenum causes enterogastric reflex and secretin release which causes decrease in gastrin secretion and decrease in gastrin stimulation of parietal cells
Fat/CHO in duodenum causes gastric inhibitory peptide release which results in decrease gastrin secretion and parietal HCl secretion

23
Q

Why does HCl need to be reduced in small intestine?

A

Enzymes secreted from the pancreas have an optimum pH of about neutral - acidic pH from HCl would denature those enzymes

24
Q

What are enterogastrones?

A

Hormones released from gland cells in duodenal mucosa (e.g. secretin, cholecystokinin (CCK), GIP)

25
Q

When are enterogastrones released?

A

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

26
Q

What is the function of enterogastrones?

A

Act collectively to prevent further acid build up in duodenum

27
Q

What are the 2 strategies for enterogastrones to carry out their function?

A

Inhibit gastric acid secretion

Reduce gastric emptying (inhibit motility/contract pyloric sphincter)

28
Q

What causes hypertonicity in duodenum?

A

Molecules coming out of the stomach

29
Q

What is pepsinogen secreted by?

A

Chief cells

30
Q

What in the inactive precursor of pepsinogen?

A

Zymogen

31
Q

What is the effect of low pH < 3 on pepsinogen?

A

Turns into pepsin through acid hydrolysis

32
Q

What does the storage of zymogen prevent?

A

Cellular digestion

33
Q

What are pepsins inactivated?

A

At a neutral pH

34
Q

What is gastric mucus produced by?

A

Surface epithelial cells and mucus neck cells

35
Q

What is the cytoprotective role of gastric mucus?

A

Protects mucosal surface from mechanical injury

Neutral pH protects against gatric acid corrosion and pepsin digestion

36
Q

What is the only essential function of the stomach?

A

Intrinsic factor

37
Q

What is intrinsic factor produced by?

A

Parietal cells

38
Q

What is intrinsic factor required for?

A

Vitamin B12 absorption

39
Q

Where is the intrinsic factor/B12 complex absorbed from?

A

Tail end of the ileum

GI - Year 2 (39 decks)

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