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BMS13 > Gastrointestinal Secretions > Flashcards

Gastrointestinal Secretions Flashcards

1
Q

How much water leaves the gut in 24 hours?

A

~150ml

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2
Q

Where is water absorbed in the gut?

A

Small intestine

Large intestine

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3
Q

What is the cephalic phase of digestion? (3)

A

Thinking about food/presence of food in mouth promotes salivary and gastric secretions

Chewing breaks food down into smaller particles

Amylase in saliva initiates starch digestion

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4
Q

What controls the cephalic phase of digestion?

A

CNS

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5
Q

What is the gastric phase of digestion? (3)

A

Stomach secretes in response to presence of food in stomach

Gastric motility for further mechanical breakdown

Protein digestion starts

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6
Q

What controls the gastric phase of digestion?

A

CNS

ENS

Hormones

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7
Q

What is the intestinal phase of digestion? (3)

A

Food entering small intestine gradually causes release of hormones that inhibit gastric secretion and motility

Hormones provoke release of biliary and pancreatic secretions into duodenum

Digestion and absorption

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8
Q

What controls the intestinal phase of digestion?

A

Mostly ENS (some CNS)

Hormones

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9
Q

Which cells in salivary glands produce saliva?

A

Acinar cells

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10
Q

Describe the process by which the primary salivary secretion is produced. (6)

A

BL Na/K-ATPase moves Na out of cell

BL NKCC2 allows 2Cl to enter cell; Cl also enters in exchange for HCO3

BL K channel

Cl leaves cell via luminal channels

Negative charge in lumen attracts Na paracellularly

Water follows by osmosis and aquaporins

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11
Q

What is the tonicity of the primary salivary secretion in relation to plasma?

A

Isotonic

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12
Q

When is the primary salivary secretion modified?

A

As it passes along the duct

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13
Q

How is the primary salivary secretion modified?

A

Some Na and Cl reabsorbed (tight junctions prevent paracellular movement back) which also results in water reabsorption

K and HCO3 added

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14
Q

Describe the secretion produced after the primary salivary secretion has been modified.

A

HCO3 rich, hypotonic secretion

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15
Q

How does high flow rate affect the tonicity of saliva (compared to plasma) and why?

A

Modification is less effective

Less hypotonic

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16
Q

What are the other components of saliva (other than Na, Cl, water, K, HCO3)?

A

Calcium and phosphate

Large molecule components (mucins, lysozyme, amylase)

IgA

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17
Q

How are large molecule components transported into saliva?

A

Produced by acinar cells and released by exocytosis

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18
Q

What cells produce the IgA in saliva?

A

Nearby plasma cells of salivary gland

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19
Q

What are the functions of saliva? (4)

A

Lubrication

Amylase initiates starch digestion

Antimicrobial activities

pH and ions protect teeth from demineralisation

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20
Q

What is the relative amount of amylase and mucus in saliva produced by the parotid gland?

A

Amylase > mucus

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21
Q

What is the relative amount of amylase and mucus in saliva produced by the submandibular gland?

A

Amylase < mucus

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22
Q

What is the relative amount of amylase and mucus in saliva produced by the sublingual gland?

A

Mucus and no amylase

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23
Q

Which salivary gland has the highest flow rate during basal conditions?

A

Submandibular

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24
Q

Which salivary gland has the highest flow rate during stimulation (eg. by eating)?

A

Parotid

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25
Q

How does ANS control generally affect saliva?

A

Parasympathetic - increase formation of fluid and electrolyte components

Sympathetic - increase release of large molecule components

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26
Q

Describe the glands in the oesophagus.

A

Widespread minor glands which only produce mucus

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27
Q

What do gastric chief/peptic cells produce?

A

Pepsinogen

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28
Q

What do gastric parietal cells produce?

A

HCl and intrinsic factor

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29
Q

What is another name for a gastric parietal cell?

A

Oxyntic cell

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30
Q

What do the gastric enterocytes produce?

A

Mucus

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31
Q

What are the main gastric secretions? (6)

A

Pepsinogen

HCl

Intrinsic factor

Mucus

Gastric lipase

Water

32
Q

What does intrinsic factor bind?

A

Vitamin B12/cobalamin

33
Q

Describe the mechanism of gastric acid secretion. (4)

A

Main drive is H/K-ATPase

Carbonic acid dissociates into HCO3 (into blood exchanged for Cl) and H+ (into lumen via ATPase)

K and Cl balance maintained by luminal channels

Water follows net ion movement into lumen

34
Q

How much more acidic is the stomach lumen than the blood?

A

3 times

35
Q

How does gastric acid secretion increase in response to stimulation?

A

Resting = proton pumps confined to intracellular tubulovesicles

Stimulated = tubulovesicles rearrange and fuse with canaliculi (continuous with luminal membrane)

36
Q

Describe how stomach distension/presence of food in mouth affects gastric acid secretion.

A

Triggers CNS/ENS = ACh released which acts on:

  • M3 receptors on parietal cells
  • Activates enterochromaffin-like cells = histamine = H2 receptors on parietal cells

Protein and amino acids in stomach cause gastrin release from G cells which travel via blood to bind CCKB receptors on parietal cells

Increased gastric acid secretion

37
Q

What is the effect of ACh on D cells?

A

Binds muscarinic receptor to release somatostatin

38
Q

What negative feedback system prevents oversecretion of stomach acid in response to ACh?

A

ACh binds muscarinic receptors on D cells to release somatostatin

SST:

  • Inhibits ECL cells
  • Inhibit G cells
  • Directly inhibit parietal cells
39
Q

Which endocrine factors affect the stomach and where are they released from? (5)

A

Gastrin from pyloric antrum

Cholecystokinin from duodenal wall

Secretin from duodenal wall

GIP from small intestine

GLP-1 from ileum/colon

40
Q

What is another name for cholecystokinin?

A

Pancreozymin

41
Q

How does gastrin affect the stomach?

A

Induces gastric secretions

Increases motility

42
Q

What affects the release of gastrin (non-hormonal)?

A

Stimulated by proteins, coffee, alcohol…

Inibited by low gastric pH

43
Q

How does cholecystokinin affect the stomach?

A

Depresses gastric motility and secretion

44
Q

What stimulates the release of cholecystokinin from the duodenal wall?

A

Fats

45
Q

How does secretin affect the stomach?

A

Inhibits gastric secretion

46
Q

What stimulates the release of secretin from the duodenal wall?

A

Acid

47
Q

How do GIP and GLP-1 affect the stomach?

A

Inhibit gastric motility and secretion

48
Q

What stimulates the release of GIP and GLP-1?

A

Fat and chyme in lumen

49
Q

What is secreted to achieve efficient absorption in the small intestine? (4)

A

Mucus (goblet cells)

Isotonic saline (crypt cells)

Alkaline mucus (Brunner’s glands)

Digestive enzymes and HCO3 rich fluid (surface enterocytes)

50
Q

Where are the digestive enzymes produced by small intestine enterocytes found?

A

Embedded in the glycocalyx of their brush border

51
Q

The relaxation of which sphincter allows secretions to enter the duodenum?

A

Sphincter of Oddi

52
Q

What are the two main components of pancreatic exocrine secretions and what produces them?

A

Alkaline, HCO3-rich fluid by pancreatic duct cells

Digestive enzymes by acinar cells

53
Q

Why are pancreatic secretions alkaline?

A

To neutralise acidic chyme entering from stomach

54
Q

How are the digestive enzymes of pancreatic secretions stored before exocytosis?

A

Intracellularly as inactive precursor forms in zymogen granules

55
Q

What hormones affect pancreatic exocrine secretion and where are they released from?

A

Cholecystokinin

Secretin

Both from duodenal wall

56
Q

How does cholecystokinin affect the pancreas?

A

Induces release of enzyme-rich secretions

57
Q

How does secretin affect the pancreas?

A

Induces release of HCO3-rich secretions

58
Q

Describe the mechanism of alkaline fluid secretion by pancreatic duct cells. (6)

A

Driven by BL Na/K-ATPase

BL Na and HCO3 move into cell in exchange for H

CO2 from blood => carbonic acid in cells (carbonic anhydrase) => HCO3 + H

HCO3 into lumen via anion exchanger (Cl into cell)

Cl leaks into lumen

Negative charge in lumen attracts Na paracellularly and water by osmosis

59
Q

What disorder can affect the alkaline fluid secretion of pancreatic duct cells and why?

A

Cystic fibrosis

Defect in Cl channels (CTFR-type)

60
Q

What does the primary biliary secretion consist of? (4)

A

Solutes extracted from blood by hepatocytes

Bile salt/acids

Bile pigments

Cholesterol and lecithin

61
Q

When is the primary biliary secretion modified?

A

As it passes along bile duct

62
Q

How is the primary biliary secretion modified?

A

Water and HCO3 added (similar to pancreatic alkaline secretion)

63
Q

What stimulates the modification of the primary biliary secretion?

A

Secretin

64
Q

What causes the gall bladder to contract and the sphincter of Oddi to relax?

A

Cholecystokinin

65
Q

What does GIP do?

A

Stimulates insulin release (feed-forward)

66
Q

What does GLP-1 do?

A

Stimulates insulin release (feed-forward)

Inhibits glucagon release

Promotes satiety

67
Q

Which hormones promote satiety?

A

Cholecystokinin

GLP-1

68
Q

What is ghrelin and what inhibits its release?

A

Hunger hormone (promotes appetite)

Food digestion

69
Q

What ions are secreted in the colon?

A

K+

HCO3-

70
Q

Describe the secretory/reabsorptive process in the colon. (4)

A

Na/K-ATPase drives process

Luminal Na channel allows Na to enter cell; Na enters in exchange for H

More Na is absorbed than Cl = negative charge in lumen driving K paracellularly into lumen

Water follows sodium paracellularly and via aquaporins for reabsorption

71
Q

What can inadequate production of saliva lead to? (4)

A

Dry mouth

Difficulty swallowing

Enamel damage

Reduced microbiological protection

72
Q

What can gastric atrophy lead to?

A

Lack of intrinsic factor

Pernicious anaemia

73
Q

What can gastritis lead to?

A

Gastric (and duodenal) ulcers

74
Q

What can excess gastric acid production lead to? (3)

A

Duodenal ulcers

Malabsorption

Diarrhoea

75
Q

What can pancreatitis lead to?

A

Inadequate enzyme production so malabsorption

76
Q

How does cystic fibrosis affect digestion?

A

Decreased Cl conductance so decreased formation of pancreatic alkaline fluid

Decreased delivery of enzymes to duodenum so less digestion

77
Q

What can insufficient biliary secretions lead to?

A

(Fat) malabsorption

BMS13 (7 decks)

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