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Gastrointestinal physiology > Gastrointestinal hormones > Flashcards

Gastrointestinal hormones Flashcards

1
Q

What do GI hormones regulate?

A

Feeling of hunger, motility, insulin release, secretion (of gastric acid, digestive enzymes)

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2
Q

Describe how most GI hormones begin as?

A

Larger precursors (often from same preprohormone product)

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3
Q

Why do GI hormones have short half life?

A

Inactivation and cleavage by peptidases (3-5mins)

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4
Q

Where are gut endocrine cells found?

A

Scattered in gut epithelium in crypts in villi

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5
Q

Describe structure of gut endocrine cells

A

Most have microvilli on apex opening to gut lumen (sense its contents)

Nutrient sensing apical GPCRs

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6
Q

What do gut endocrine cells sense/respond to?

A

Respond to carbs, bile salts lipids and proteins

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7
Q

From which surface of endocrine cells are gut hormones released?

A

Basally

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8
Q

What are the different routes for gut endocrine secretions?

A

Endocrine/paracrine, neuroendocrine (enteric nervous system)

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9
Q

What stimulates release of gut hormones?

A

Mechanical/electrical presence of food

Cephalic phase

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10
Q

What region(s) are hormones released from? What is the most common?

A

Stomach, duodenum, and colon

Small intestine is the most common

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11
Q

What mechanism releases peptide hormones?

A

Exocytosis

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12
Q

What layer are gut endocrine cells derived from?

A

Endoderm

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13
Q

What 2 structures release peptide hormones?

A

Gut endocrine cells

Nerves of ENS (endocrine)

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14
Q

Integrated role of gut endocrine and nervous systems…

A

Control motor/digestive/vascular activity of the gut

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15
Q

What are 2 families of gut hormones?

A

Gastrin like and secretin like

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16
Q

Example of gastrin like hormones

A

Gastrin, CCK

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17
Q

Example of secretin like hormones

A

VIP, secretin, GIP, glucagon

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18
Q

Which hormones regulate digestion (4)?

A

Histamine, somatostatin, secretin, gut glucagon

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19
Q

What hormone regulates digestion and appetite (1)?

A

CCK

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20
Q

What do the incretin hormones do, give an example?

A

Regulate insulin secretion

GIP and GLP1

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21
Q

Which hormones are released in stomach?

A

Histamine, gastrin, ghrelin and somatostatin

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22
Q

What hormone is released by duodenum?

A

Gastrin

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23
Q

What hormones are released by small intestine and colon?

A

VIP, CCK, PYY, GIP, GLP1

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24
Q

What cell makes histamine?

A

ECL cells of stomach

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25
Q

What is histamine made from, and how (enzyme)?

A

Histidine by histidine decarboxylase

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26
Q

What stimulates histamine release

A

Gastrin, vagal stimulation, and stretch

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27
Q

What are the actions of histamine?

A

Local paracrine action stimulate HCl secretion via H2 receptors on parietal cell

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28
Q

What receptor and what cell does histamine act on?

A

H2 receptor on parietal cells

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29
Q

Where is Gastrin synthesised?

A

G cells of gastric antrum crypts and duodenal cells

30
Q

What factors stimulate gastrin secretion (4)?

A

Luminal protein digestion products (e.g. AA)

Vagus (via ACh + gastrin release peptide)

Stomach distention

Hypercalcaemia

31
Q

What inhibits gastrin release?

A

Stomach pH<2.5 (H+ -ve feedback)

Somatostatin (and secretin)

32
Q

What part of stomach makes gastrin?

A

Gastric antrum

33
Q

What are the actions of gastrin (5)?

A

Stimulate gastric acid secretion via
insertion of K+/H+ ATPase into apical membrane of parietal cells

Parietal cell growth

Pepsinogen secretion secretion

Antral motility and mucosal blood flow

Water and electrolyte secretion in liver, pancreas and intestine

34
Q

How does gastrin stimulate gastric acid secretion (2 ways)?

A

Directly via binding to parietal cell to induce apical expression of K+/H+ATPase

Indirectly binding to ECL cells to induce release of histamine (which acts on H2)

35
Q

What receptor does gastrin bind to on parietal cells?

A

CCK-B

36
Q

What are ECL cells?

A

Enterochromaffin-like cells or ECL cells are a type of neuroendocrine cell secreting histamine.

37
Q

Where is secretin made?

A

From duodenum to ileum (S cells in the neck of crypts)

38
Q

What cells secrete secretin?

A

S cells

39
Q

Describe distribution of S cells from duodenum to distal ileum?

A

Fewer

40
Q

What stimulates secretin release?

A

Acid in proximal duodenum

41
Q

What inhibits secretin release?

A

Somatostatin

42
Q

What are the effects of secretin?

A

Stimulate pancreatic secretions of HCO3- and water (wash pancreatic enzymes into gut)

Stimualte liver secretion of HCO3- and water into bile
(potentiate CCK, calcitonin PTH secretion)

Controlling gut pH

Reduces acid secretion by parietal cells of the stomach.

43
Q

Which gut hormone is important for controlling gut pH?

A

Secretin

44
Q

How does secretin reduce acid secretion by the stomach parietal cells?

A

Stimulating release of somatostatin

Inhibiting release of gastrin in the pyloric antrum

Direct downregulation of the parietal cell acid secretory mechanics.

45
Q

What cells secrete somatostatin, where?

A

D cells in gastric antrum to colon

46
Q

What is the function of somatostatin?

A

Suppresses secretion of GI hormones

Suppresses their effects (acid etc)

Retards absorption glucose (protects against post-prandial hyperglycaemia)

47
Q

Where is VIP released?

A

Enteric neurons in pelvic parasympathetic nerves also in brain and in nerves in pancreas

48
Q

What triggers VIP release

A

Unknown: not food releated

49
Q

What triggers somastatin release?

A

Stimulated by meals: amino acids, glucose, fatty acids, gastrin, secretin.

50
Q

What does VIP do?

A

Relaxes cardiac sphincter, stomach, anal sphincter; vasodilator. Causes pancreatic bicarbonate secretion.

51
Q

What cells secrete motilin ?

A

Mo cells from antrum to colon

52
Q

What is motilin thought to be involved with?

A

Initiating the MMC (migrating myoelectric motility complex)

53
Q

What cells secret gut glucagon and where?

A

Gastric A cells

Ilial, colonic L cells

54
Q

What effect does gut glucagon have?

A

Stimulates gastric/intestinal motility, stimulates intestinal absorption sugars, systemic glucagon-like effects.

55
Q

Where is CCK made?

A

I cells in duodenum and jejunum

56
Q

What stimulates release of CCK?

A

Protein and fat digestion products in duodenum

57
Q

What are the actions of CCK (3)?

A

Stimulate secretion of pancreatic enzymes and potentiates secretin action

Contraction of gall bladder

Causes satiety by signalling on vagal afferent terminals

58
Q

Which enzyme can potentiate secretin?

A

CCK

59
Q

Which hormone stimulates gall bladder contraction and pancreatic enzyme secretion?

A

CCK

60
Q

Which enzyme stimulates HCO3- excretion?

A

Secretin

61
Q

What hormone stimulates pepsin and gastric acid secretion?

A

Gastrin

62
Q

What releases GLP1?

A

L cells in small intestine

63
Q

When is GLP1 released?

A

Meals, carbs, fat and GIP

64
Q

What does GLP1 do?

A

Potentiates glucose stimulated insulin release (sensitises beta cells to glucose)

Suppresses appetite

65
Q

What secrets GIP?

A

K cells small intestine

66
Q

What does GIP do?

A

Potentiates glucose stimulates insulin release

67
Q

What stimulates GIP production?

A

Oral, glucose, fat and protein

68
Q

What hormone is important in gall bladder contraction?

A

CCK

69
Q

What hormone is important in pancreatic enzyme secretion?

A

CCK

70
Q

Where is CCK secreted from?

A

Duodenum

71
Q

What is CCK secreted in response to?

A

Chyme in duodenum

Gastrointestinal physiology (5 decks)

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