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07. Year 2: Alimentary System > Gastric Secretion > Flashcards

Gastric Secretion Flashcards

1
Q

What are some areas of the stomachs anatomy?

A

Fundus

Body

Antrum

Pyloris region

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2
Q

What is the function of the fundus of the stomach?

A

Storage

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3
Q

What are the functions of the body of the stomach?

A

Storage

Mucus protects stomach surface

Produce hydrochloric acid

Pepsinogen production

Intrinsic factor production

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4
Q

What is the function of mucus in the stomach?

A

Protect the surface of the stomach

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5
Q

What causes the low pH of the stomach?

A

Presence of hydrochloric acid

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6
Q

Why is pepsinogen in the stomach and not pepsin?

A

Active pepsin would digest the stomach itself as it is made of proteins

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7
Q

What is the function of intrinsic factor?

A

Required for vitamin B12 absorption

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8
Q

What are the functions of the antrum?

A

Mixing/grinding (mix secretions with content of diet and grind them down)

Gastrin production

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9
Q

What is the function of gastrin?

A

Enter circulation system (is a hormone) and come back to the body of the stomach where it switches on hydrochloric acid and pepsinogen secretion

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10
Q

Where in the stomach is hydrochloric acid secreted?

A

Body

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11
Q

Where in the stomach is pepsinogen secreted?

A

Body

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12
Q

Where in the stomach is gastrin secreted?

A

Antrum

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13
Q

What is found in gastric pits?

A

Surface mucous cells

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14
Q

What area is deep to the gastric pit?

A

Gastric gland

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15
Q

What cells make up the gastric gland?

A

Mucous neck cell

Parietal cell

Chief cell

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16
Q

What do mucous neck cells secreted?

A

Mucus

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17
Q

What do chief cells secreted?

A

Pepsinogen

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18
Q

What do parietal cells secrete?

A

Hydrochloric acid

Intrinsic factor

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19
Q

Why are surface mucous cells found superficial to the gastric gland?

A

To protect us from the secretions of the gastric gland

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20
Q

What happens do mucous neck cells once they mature?

A

They become surface mucous cells

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21
Q

What is the pH of blood?

A

7.4

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22
Q

What is the mechanism of parietal cell secretions?

A

1) Carbon dioxide is present in the blood which diffuses across the cell membrane into cell
2) CO2 combines with H2O in the cytoplasm which is controlled by enzyme carbonic anhydrase
3) Forms unstable H2CO3 which dissociates into H+ and HCO3 (bicarbonate)
4) H+ ion pumped by H/K ATPase up to its concentration gradient out of the cell while K is pumped in (1:1 ratio)
5) Bicarbonate is transferred out of the cell at baseolateral membrane for Cl
6) Cl exits alongside H+ ion into stomach lumen
7) Osmotic gradient due to H+ and Cl leaving the cell causes water to transfer across from the blood into the stomach
8) pH of stomach is less than 2 because of hydrogen ions being pumped into stomach
9) Because bicarbonate transferred out into blood the pH increases a bit over 7.4

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23
Q

What pump causes the stomach pH to be less than 2?

A

H/K ATPase pumping H+ into the stomach lumen

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24
Q

What enzyme allows CO2 to combine with H2O?

A

Carbonic anhydrase

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25
Q

What are examples of things that activates the K/K ATPase pump?

A

Histamine

Acetylcholine

Gastrin

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26
Q

What is an example of something that inhibits the H/K ATPase pump?

A

Prostaglandins

27
Q

What is the mechanism of gastrin activating the H/K ATPase pump?

A

1) Gastrin binds with receptor on parietal cell that is coupled up to a system that increases intracellular Ca2+
2) Ca2+ acts on protein kinases to switch on H/K ATPase causing more hydrogen to be pumped into the stomach

28
Q

What is the mechanism of histamine activating the H/K ATPase pump?

A

1) Histamine acts on receptor on parietal cell (unique histamine receptor for stomach, type 2 receptor whereas everywhere else is type 1)
2) Coupled with Gs that act on AC causing the conversion of ATP to cAMP
3) cAMP acts on protein kinases that turn on H/K ATPase pump

29
Q

What is the mechanism of acetylcholine activating the H/K ATPase pump?

A

1) Acts on muscurinic cholinergic receptor that is coupled up to a system that increases Ca2+ intracellular levels
2) Ca2+ acts on protein kinases that turn on H/K ATPase pump

30
Q

What is the mechanism of prostaglandins inhibiting the H/K ATPase pump?

A

1) Acts on receptor that is bound to inhibitor protein Gi
2) Inhibits conversion of ATP to cAMP
3) So reduces activation of protein kinases and turns off H/K ATPase pump

31
Q

What kind of mediator is histamine?

A

Paracrine mediator

32
Q

What kind of mediator is acetylcholine?

A

Nervous mediator

33
Q

What are the 3 mechanisms that controls gastric acid secretion?

A

Neurocrine (vagus/local reflexes)

Endocrine (gastrin)

Paracrine (histamine)

34
Q

What are the two phases for stimulating gastric acid secretion?

A

1) Cephalic phase
2) Gastric phase

35
Q

What is the mechanism of the cephalic phase stimulating gastric acid secretion?

A

1) Thinking, seeing or tasting food activates the vagus nerve
2) Releases acetylcholin which activates parietal cells
3) Vagus nerve also acts on G cells that secretes gastrin and switches on parietal cells
4) Locally, gastrin and acetylcholine also act on ECL cells that releases histamine that activates parietal cells

36
Q

What is the mechanism of the gastric phase for gastric acid secretion?

A

1) Presence of food in stomach causes distension of stomach (stretch in wall)
2) Activates vagul/enteric (enteric nervous system) reflexes
3) Both release acetylcholine which activates parietal cells
4) Or peptides arrive in lumen stimulate G cells that release gastrin that activates parietal cells
5) Or gastrin/acetycholine acts on ECL cells which releases histamine that activates parietal cells

37
Q

Why is the cephalic phase of gastric secretion important?

A

Stomach must be ready with acid to kill pathogens before they arrive

38
Q

What are the 3 phases for inhibiting gastric acid secretion?

A

Cephalic phase

Gastric phase

Intestinal phase

39
Q

What kind of loop is the gastric phase of gastric acid secretion?

A

Negative feedback because as the pH falls due to the rise of hydrochloric acid the concentration of gastrin is decreased

40
Q

What is the mechanism for the cephalic phase in inhibiting gastric acid secretion?

A

1) Stop eating
2) Vagal activity decreases

41
Q

What is the mechanism for the gastric phase for inhibiting gastric acid secretion?

A

1) pH in stomach decreases due to concentration of hydrochloric acid rising
2) Concentration of gastric decreases

42
Q

What is the mechanism of the intestinal phase for the inhibition of gastric acid secretion?

A

1) Acid present in the duodenum activates the enterogastric (splanchnic) reflex and/or causes secretin release
2) Both inhibit gastrin secretion which decreases gastrin stimulation of parietal cells

or

1) Fat or carbohydrates in duodenum
2) GIP is released
3) Inhibits gastric secretion decreasing parietal hydrochloric acid secretion

43
Q

What are enterogastrones?

A

Hormones released from gland cells in duodenal mucosae

44
Q

What are examples of enterogastrones?

A

Secretin

Cholecystokinin (CCK)

GIP

45
Q

What are examples of things that when they enter the duodenum they activate the release of enterogastrones?

A

Acid

Hypertonic solutions

Fatty acids

Monoglycerides

46
Q

What is the function of enterogastrones?

A

Act collectively to prevent further acid build up in the duodenum

47
Q

What 2 strategies do enterogastrones use to preven acid build up in the duodenum?

A

Inhibit gastric gland secretion

Reduce gastric emptying (inhibit motility/contract pyloric sphincter)

48
Q

What is a zymogen?

A

Inactive precurser

49
Q

What is pepsinogen secreted by?

A

Chief cells

50
Q

What is pepsinogen the zymogen of?

A

Pepsin

51
Q

Why is pepsin stored as a zymogen (pepsinogen)?

A

Prevents cellular digestion

52
Q

When is pepsin inactive and why is this important?

A

At neutral pH so is not active in the duodenum

53
Q

What are the mechanisms for controlling pepsin secretion?

A

Same as those for hydrochloric acid secretion, using activators such as acetylcholine and histamine

54
Q

What is a consequence of the mechanisms for pepsin control using the same substances as the mechanisms for hydrochloric acid secretion?

A

When pepsin is secreted so is hydrochloric acid

55
Q

What is gastric mucus produced by?

A

Surface epithelial cells and mucous neck cells

56
Q

What is the role of mucus described as?

A

Cytoprotective (protection against harmful agents)

57
Q

What are the functions of mucous in the stomach?

A

Protects the mucosal surface from mechanical injury

Has neutral pH so protects against gastric acid corrosion and pepsin digestion

58
Q

What substance does mucus have a high content of?

A

Bicarbonate

59
Q

What is a consequence of mucus having a high bicarbonate content?

A

Has a neutral pH

60
Q

What does mucus form above the epithelium and why is this important?

A

As mucus is secreted meets the pH 2 gastric juice and forms mucous layer

So by the time acid reaches the pH 7 cell surface the acid is effectively denatured

61
Q

What is intrinsic factor produced by?

A

Parietal cells

62
Q

For absorption of what is intrinsic factor crucial for?

A

Vitamin B12

63
Q

Where is the vitamin B12/intrinsic factor complex absorbed from?

A

Ileum

64
Q

What does a defect in the intrinsic factor lead to?

A

Pernicious anaemia

07. Year 2: Alimentary System (41 decks)

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