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Alimentary System > Lecture 7 Gastric Secretion > Flashcards

Lecture 7 Gastric Secretion Flashcards

1
Q

What is the Antrum

A

This is the wider part of the pylorus, which is the narrower part of the stomach. It resides upstream from the pyloric canal and its junction of the pyloric sphincter to the duodenum

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2
Q

Define pepsinogens

A

Precursor protein digesting enzymes

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3
Q

Mucous neck cells in the gastric glands secrete

A

Mucus

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4
Q

Chief cells in the gastric glands secrete

A

pepsinogens

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5
Q

Parietal cells in the gastric glands secrete

A

HCl

Intrinsic factor

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6
Q

What is the concentration of HCl in the parietal cells compared to the blood

A

3-million fold higher

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7
Q

What type of gradient is chloride secreted against

A

Concentration and electrical

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8
Q

What is the ability of parietal cells to secrete acid dependent on

A

Active transport using the H+/ATPase or proton pump

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9
Q

Where is the proton pump located

A

near the lumen of the gastric pit in the canalicular membrane

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10
Q

How are hydrogen ions generated

A

Dissociation of water

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11
Q

How is bicarbonate ion formed in the parietal cell

A
  • Hydrogen ions are generated within the parietal cell from dissociation of water
  • The hydroxyl ions formed in this process rapidly combine with carbon dioxide to form bicarbonate ion, a reaction catalysed by carbonic anhydrase
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12
Q

What is the alkaline tide and what is its purpose

A
  • Bicarbonate is transported out of the basolateral membrane in exchange for chloride
  • The outflow of bicarbonate into blood results in slight elevation of blood pH known as “alkaline tide”. This process serves to maintain intracellular pH in the parietal cell
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13
Q

What is necessary for the secretion of acid

A

• Chloride and potassium ions are transported into the lumen of the canaliculus by conductance channels

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14
Q

How does outward diffusion of water occur from the parietal cell

A
  • Hydrogen ion is pumped out of the cell, into the lumen, in exchange for potassium through the action of the proton pump and potassium is recycled
  • Accumulation of osmotically active hydrogen ion in the canaliculus generates an osmotic gradient across the membrane that results in outward diffusion of water
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15
Q

How is gastric acid secretion controlled

A
  • Neurocrine – Vagus/local reflexes
  • Endocrine – gastrin
  • Paracrine- histamine
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16
Q

What is histamine’s effect on the parietal cells

A

Activates adenylate cyclase which leads to elevation of cAMP concentrations and activates protein kinase A
PKA phosphorylates cytoskeleton involved in transport of the H+/k+ ATPase pump from cytoplasm to plasma membrane

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17
Q

What is the action of acetylcholine and gastrin binding onto receptors on parietal cells

A

Elevation of intracellular calcium

This leads to activation of PKA

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18
Q

What neuroendocrine cells can Gastrin and Acetylcholine act on to cause the release of histamine

A

Enterochromaffin Cells

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19
Q

What a G cells

A

a type of cell in the stomach and duodenum that secretes gastrin. It works in conjunction with gastric chief cells and parietal cells.

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20
Q

Where a G cells found

A

G cells are found deep within the pyloric glands of the stomach antrum, and occasionally in the pancreas and duodenum

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21
Q

Where are G cells found

A

Deep within pyloric glands of the stomach antrum and occasionally in pancreas and duodenum

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22
Q

Describe the gastric phase of secretion

A

When there is distension in the stomach the vagal/enteric reflexes are activated leading to the release of Act.
Peptides in the lumen cause the relate of gastrin from G cells and Act and G cells act on ECL cells to release histamine and all 3 act on parietal cell

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23
Q

Define the gastric phase

A

Occurs while food is in the stomach. 60% of total secretion
Vagal and enteric nerves
Paracrine (local) hormones (histamine) and endocrine hormones (gastrin)

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24
Q

What inhibits the secretion of gastrin

A

Lumen pH <2

25
Q

How does the intestinal phase end

A

Acid in the duodenum leads to aplnchnic reflex that caused a decreased of gastrin secretion and the release of GIP which also reduces gastrin secretion and HCl

26
Q

What are the mechanisms of the cephalic phase

A

The sight, smell and taste of food causes an increase in activity of the vagus nerve which stimulates the release of Ach and G cells which release gastrin
Gastrin and Ach act on ECL cells which release histamine

27
Q

What are the mechanisms for the gastric phase

A

Distension in the stomach is detected by vagal/enteric reflexes which leads to the release of Ach
peptides in lume G cells release Gastrin
Gastrin and Ach act on ECL which release gastrin

28
Q

What stops the cephalic phase of gastric secretion

A

Decrease in pH (increase in HCl) which reduces the amount of gastrin

29
Q

What stops the intestinal phase

A

Splanchnic reflex, secretin release and GIP release

30
Q

What are Enterogastrones

A

Hormones released from gland cells in duodenal mucosa- secretin, cholecystokinin (CCK), GIP

31
Q

What are enterogastrones

A

Hormones released from gland cells in duodenal mucosa- secretin, cholecystokinin (CCK), GIP

32
Q

What is the function of enterogastrones

A

• Released in response to acid, hypertonic solution, fatty acids or monoglycerides in duodenum
• Act collectively to prevent further acid build up in duodenum
• Two strategies
o Inhibit gastric secretion
o Reduce gastric emptying (inhibit motility/contract pyloric sphincter)

33
Q

What is pepsinogen and what is it secreted by

A

(zymogen = inactive precursor) secreted by chief cells

34
Q

Why is pepsin kept as a zymogen

A

Prevents cellular digestion and is activated at low pH (more acidic)

35
Q

What is the role of gastric mucus

A

produced by surface epithelial cells and mucous neck cells. protect mucosal surface from mechanical injury and gastric acid corrosion and pepsin digestion

36
Q

Where are intrinsic factors produced

A

Parietal cells

37
Q

Why are intrinsic factors essential

A

Vitamin B12 absorption

38
Q

What happens when there is a defect in Intrinsic factor and Vitamin B12 absorption

A

Pernicious Anaemia (failure of erythrocyte maturation)

39
Q

Describe the Cephalic phase of gastric acid secretion

A

When there is sight, smell or taste of food the vagus nerve activity increases leading to the release of ch and Gastrin from G cells. Gastrin and School bind to ECL cells to release Histamine and all three bind to parietal cells

40
Q

What are Enterochromaffin Cells

A

distinctive type of neuroendocrine cell in the gastric mucosa underlying the epithelium that release histamine

41
Q

What are G cells

A

a type of cell in the stomach and duodenum that secretes gastrin. It works in conjunction with gastric chief cells and parietal cells

42
Q

Where are G cells found

A

Deep within pyloric glands of the stomach antrum and occasionally in pancreas and duodenum

43
Q

Describe the gastric phase of secretion

A

When there is distension in the stomach the vagal/enteric reflexes are activated leading to the release of Act.
Peptides in the lumen cause the relate of gastrin from G cells and Act and G cells act on ECL cells to release histamine and all 3 act on parietal cell

44
Q

How does the Cephalic phase end

A

Decrease in vagal activity

45
Q

How does the gastric phase end

A

Decrease in pH (increase in HCl) and a decrease in Gastrin

46
Q

How does the intestinal phase end

A

Acid in the duodenum leads to aplnchnic reflex that caused a decreased of gastrin secretion and the release of GIP which also reduces gastrin secretion and HCl

47
Q

When does the cephalic phase occur

A

Before food enters stomach and is 30% of secretion

48
Q

When does the gastric phase occur

A

When the food is in the stomach >60% of secretion

49
Q

When does the intestinal phase occur

A

Occurs after food enters the small intestine and is largely hormonal

50
Q

What stimulates the intestinal phase

A

Gastrin

51
Q

What inhibits the intestinal phase

A

GIP, secretin, cholecystokinin

52
Q

What are enterogastrones

A

Hormones released from gland cells in duodenal mucosa- secretin, cholecystokinin (CCK), GIP

53
Q

What is the function of enterogastrones

A

• Released in response to acid, hypertonic solution, fatty acids or monoglycerides in duodenum
• Act collectively to prevent further acid build up in duodenum
• Two strategies
o Inhibit gastric secretion
o Reduce gastric emptying (inhibit motility/contract pyloric sphincter)

54
Q

What is pepsinogen

A

A zymogen that is secreted by chief cells

55
Q

Why is pepsin kept as a zymogen

A

Prevents cellular digestion and is activated at low pH (more acidic)

56
Q

What is the role of gastric mucus

A

produced by surface epithelial cells and mucous neck cells. protect mucosal surface from mechanical injury and gastric acid corrosion and pepsin digestion

57
Q

What is Intrinsic Factor

A

Produced by paritetal cells and are required for Vitamin B12 absorption from ileum

58
Q

What occurs if vitamin B12 is unable to be absorbed

A

Pernicious anaemia (failure of rbc maturation)

Alimentary System (39 decks)

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