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GI AM > Gastric secretion > Flashcards

Gastric secretion Flashcards

1
Q

What is the fundus?

A

Upper part forming the majority of the stomach

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2
Q

What is the structure of the fundus?

A

Thinner musculature

Pleats on surface allow for increase in volume

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3
Q

What is the function of the fundus?

A

Storage

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4
Q

What is the function of the body of the stomach?

A 
Storage
Mucus
HCl production for sterilisation
Pepsinogen production
Intrinsic factor production
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5
Q

What is the function of the antrum?

A

Mixing and grinding

Gastrin production

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6
Q

What is the cellular composition of gastric glands?

A

Mucous neck cells
Chief cells
Parietal cells

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7
Q

What is the function of mucous neck cells?

A

Secrete mucus

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8
Q

What are mucous neck cells?

A

Immature surface cells

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9
Q

What is the function of chief cells?

A

Secrete pepsinogen

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10
Q

What is the function of parietal cells?

A

Secrete HCl and intrinsic factor

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11
Q

How does water pass from the stomach lumen to the bloodstream?

A

Passes through tight junctions between the parietal cells

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12
Q

What happens to CO2 in the stomach lumen?

A

Passiveley enters the parietal epithelium and binds with H20 to form H2CO3

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13
Q

What happens to H2CO3 in the parietal epithelium?

A

Splits into HCO3 and H
H is transported into lumen as K is transported in
HCO3 transported into blood as Cl is transported in

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14
Q

What happens to H in the stomach lumen?

A

Binds with Cl to form HCl and lower the stomach pH

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15
Q

What secretions have an effect on the stomach?

A

Gastrin
Histamine
Acetylcholine
Prostaglandins

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16
Q

What does gastrin do?

A

Activates a receptor on the basolateral membrane causing a rise in intracellular Ca, that tells protein kinases to pump more H across the apical membrane, decreasing the pH of the stomach lumen

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17
Q

What does histamine do?

A

Stimulated the H2 receptor inducing uptake of CO2 and H2O which in turn decrease the pH of the stomach lumen

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18
Q

What does acetylcholine do?

A

Cause increase in intracellular Ca, that tells protein kinases to pump more H across the apical membrane, decreasing the pH of the stomach lumen

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19
Q

What do prostaglandins do?

A

Couple themselves to inhibited G proteins and reduce protein kinase activity to even out the pH of the stomach lumen

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20
Q

What is the main release of acetylcholine and what does it act on for the stomach?

A

Vagus nerve

Muscarinic cholinergic

21
Q

What are the 3 types of control of gastric secretion?

A

Neurocrine
Endocrine
Paracrine

22
Q

What is the neurocrine control of gastric secretion?

A

Acetylcholine from Parasympathetic- Vagus and ENS

23
Q

What is endocrine control of gastric secretion?

A

Gastrin

24
Q

What is paracrine control of gastric secretion?

A

Histamine

Local effect

25
Q

What are the 2 mechanisms stimulating gastric secretions?

A

Cephalic phase

Gastric phase

26
Q

Why is the cephalic phase of secretion important?

A

Create acidity before food arrives in the stomach so it can be sterilised immediately

27
Q

What happens in the cephalic phase of secretion?

A

Sight, smell and taste of food causes an increase in vagus activity causing Ach release and gastrin release

28
Q

What happens during the gastric phase of secretion?

A

Distension of stomach activates vagal and enteric reflexes, releasing Ach
Peptides in limen activate G cells to release gastrin
Gastrin and Ach act on ECL to release histamine

29
Q

What happens in the cephalic phase on inhibition?

A

Stop eating causes a decrease in vagal activity

30
Q

What happens in the gastric phase of inhibition?

A

Decrease of lumen pH causes a decrease in gastrin secretion so pH doesn’t drop too low

31
Q

What kind of reaction is the gastric phase of inhibition?

A

Negative feedback

32
Q

What initiates the intestinal phase of inhibition?

A

Acid or fat in duodenum

33
Q

What does acid in the duodenum cause?

A

Enterogastric reflex and secretin release, decreasing gastrin secretion and stimulation

34
Q

What does acid in the duodenum indicate?

A

Stomach is empty

35
Q

What does fat in the duodenum cause?

A

GIP release, decreasing gastrin and parietal HCl secretion

36
Q

What are enterogastrones?

A

Hormones released from gland cells in duodenal mucosa

37
Q

What are the main enterogastrones?

A

Secretin
CCK
GIP

38
Q

What are enterogastrones released in response to?

A 
Acid
Hypertonic solutions
Fatty acids
Monoglycerides 
in the duodenum
39
Q

What do enterogastrones aim to do?

A

Prevent any acid getting into the duodenum

40
Q

What are the 2 methods of action of enterogastrones?

A

Inhibit gastric secretion

Reduce gastric emptying- inhibit motility and contract pyloric sphincter

41
Q

What is pepsinogen?

A

Inactive precursor to pepsin

42
Q

What activated pepsinogen to turn into pepsin?

A

pH of below 3

43
Q

Why is pepsin stored in its inactive form?

A

To prevent cellular damage

44
Q

How is pepsin deactivated?

A

When the stomach reaches a neutral pH or pepsin enters and area of neutral pH

45
Q

What are the mechanisms for control of pepsin?

A

Sight, smell and taste of food causes an increase in vagus activity causing Ach release and gastrin release- lowering pH and activating pepsin
Distension of stomach activates vagal and enteric reflexes, releasing Ach
Peptides in limen activate G cells to release gastrin
Gastrin and Ach act on ECL to release histamine- lowering pH and activating pepsin

46
Q

Where is gastric mucus produced?

A

Epitelial cells and mucus neck cells

47
Q

What is the role of gastric mucus?

A

Cytoprotective
Protects mucosal surface from mechanical injury
Protects against gastric acid corrosion and pepsin digestion

48
Q

How does the mucus protect against gastric acid and pepsin?

A

Gastric acid neutralised by bicarbonate buffer

Pepsin deactivated by neutral pH

GI AM (34 decks)

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