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Year 1: Alimentary System > 10. Regulation of Gut Function > Flashcards

10. Regulation of Gut Function Flashcards

1
Q

What are the three mechanisms to regulate the function of the gut?

A

Nervous, paracrine and endocrine system

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2
Q

What are the two mechanisms within the nervous system?

A

Intrinsinc (enteric NS - motility)

Extrinsic (autonomic)

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3
Q

What makes up the enteric nervous system?

A

Rich plexus of ganglia (nerve cells + glial cells) interconnected by tracts of fine, unmyelinated nerve fibres

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4
Q

What is the function of the enteric nervous system?

A

Integrates the motor and secretory activities of the GI system

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5
Q

How does the enteric NS function with the central control?

A

It can do so independently - many of the motor and secretory activities are controlled the ENS

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6
Q

What are some examples of enteric neural dysfunction/degeneration?

A

Inflammation (UC and CD = IBD)
Post-operative injury
IBS
Ageing (constipation)

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7
Q

What does the enteric nervous system regulate?

A 
Motility
Blood flow 
Water and electrolytes transport
Secretion 
Absorption
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8
Q

What are the three types of neurons in the enteric nervous system?

A

Sensory
Motor
Interneurones

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9
Q

What do sensory neurons respond to?

A

Mechanical, thermal, osmotic and chemical stimuli

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10
Q

Where do motor neurons terminate?

A

Axons terminate on smooth muscle cells of the circular or longitudinal layers, secretory cells of the GI tract or GI blood vessels

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11
Q

What is the function of interneurones?

A

They integrate sensory input and effector output. They lie between neurons

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12
Q

What plexus lies in the submucosa?

A

submucosal plexus

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13
Q

What plexus lies in the muscularis externa?

A

Myenteric plexus - between the circular and longitudinal muscle

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14
Q

What is the function of the myenteric plexus?

A

Controls gut motor function

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15
Q

What is the function of the submucosal plexus?

A

Sensing environment within the lumen then regulating blood flow, epithelial and endocrine cell function

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16
Q

Give examples of minor plexuses?

A

Deep muscular plexus (inside circular muscle)

Ganglia supplying the bilary system and pancreas

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17
Q

What does the autonomic nervous system regulate?

A

Smooth muscle, cardiac muscle and glands

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18
Q

What are the two branches of the autonomic nervous system?

A

Sympathetic and parasympathetic

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19
Q

Describe the sympathetic neurons?

A

Short preganglionic neurons

Long postganglionic neurons

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20
Q

Describe parasympathetic neurons

A

Long preganglionic neurones

Short postganglionic neurons

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21
Q

Where do the cell bodies of the preganglionic neurones of the sympathetic NS lie?

A

In the thoracic and lumbar spinal cord

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22
Q

Which sympathetic nerves innervate the foregut, midgut and remainder of the gut?

A

Fore and mid gut - Thoracic splanchnic nerve

Remainder of the gut - lumbar splanchnic

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23
Q

What is the major neurotransmitter of the sympathetic nervous system?

A

Norepinephrine/noradrenaline

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24
Q

What effect does activation of the sympathetic nerves have on the GI system?

A

It tends to inhibit the activities of the GI system

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25
Q

Where do the cell bodies of the preganglionic neurons of the parasympathetic system lie?

A

In the brainstem and sacral spinal cord.

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26
Q

Where do the cell bodies of the postganglionic neurones of the sympathetic neurons lie?

A

In the pre- and para vertebral ganglia

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27
Q

Where do the cell bodies of the postganglionic neurons of the parasympathetic system lie?

A

Close to target to organs - somtimes directly onto the enteric plexi

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28
Q

What innervates most of the GI tract down to the level of the transverse colon?

A

Vagus nerve

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29
Q

Where does the descending colon, sigmoid colon, rectum and anus receive parasympathetic fibres from?

A

Pelvic nerve

30
Q

What neurotransmitter is used by parasympathetic system?

A

acetylcholine

31
Q

How does the parasympathetic affect the GI tract?

A

Excitation

32
Q

What two nerve plexuses make up the enteric nervous system?

A

Myenteric plexus and submucosal plexus

33
Q

What structures do sympathetic fibres innervate?

A

The plexuses of the enteric nervous system but also directly on the blood vessels of the GI tract - to control vasocontriction

34
Q

What does the enteric nervous system directly affect?

A

Smooth muscle
Endocrine cells
Secretory cells
Blood vessels

35
Q

What types of receptors exist on the GI tract wall?

A

Chemo and mechanoreceptors

36
Q

What do receptors on the GI tract wall feedback to?

A

Local afferents - back to the enteric nervous system

Splanchnic and vagal afferents - back to the CNS

37
Q

Where do endocrine cells exist in the gut?

A

Mucosa or submucosa of the stomach, intestine and pancreas

38
Q

What hormones does the stomach secrete?

A

Gastrin
Ghrelin
Somatostatin
Histamine

39
Q

What hormones does the duodenum secrete?

A

Secretin
CCK
Somatostatin

40
Q

What hormones does the jejunum and ileum secrete?

A 
PYY
GIP
GLP-1
GLP-2
Oxyntomodulin
Neurotensin
Somatostatin
41
Q

What hormones does the colon secrete?

A 
PYY
GLP-1
Oxyntonmodulin
Neurotensin
Somatostatin
42
Q

What hormones does the pancreas secrete?

A

Insulin
Glucagon
Somatostatin
Pancreatic polypeptide

43
Q

Where are enteroendocrine cells found?

A

In crypts near a blood supply. The nuclues is basal sided with lots secretory vesicles near the basal membrane for release into the blood. The apical membrane contains receptors for sensing nutrients

44
Q

What can enteroendocrine cells sense?

A

Amino acids
Fatty Acids
Glucose

45
Q

What is the function of the gastrointestinal endocrine system?

A

Regulation of the mechanical process of digestion
Regulation of the chemical and enzymatic process of digestion
Control post absorptive processes (GIP stimulates insulin release, PYY3-36 acts on the CNS to supress appetite)
Effects on the growth and development of the GI tract (GLP-2 promotes small intestinal growth)

46
Q

What is the effect of histamine in terms of paracrine effects?

A

Released from stomach walls - it stimulates HCl secretion by gastric parietal cells

47
Q

What is the effect of somatostatin in terms of paracrine effects?

A

Released from the stomach - it inhibits acid secretion by paracrine mechanisms

48
Q

Where is gastrin synthesised?

A

Gastric antrum and upper small intestine

49
Q

What stimulates the release of gastrin?

A

aa and peptides
Gastric distension
Vagus nerve

50
Q

What the function of gastrin?

A

Stimulates gastric acid secretion

51
Q

What inhibits the release of gastrin?

A

When pH of the stomach falls below pH 3

52
Q

Where is somatostatin synthesised?

A

All over the GI tract in endocrine D cells

53
Q

What is the function of somatostatin?

A

Universal inhibitor of:
gastric secretion, motility, intestinal and pancreatic secretions, release of gut hormones, intestinal nutrient and electrolyte transport, growth and proliferation

54
Q

When is somatostatin released?

A

in response to a mixed meal

55
Q

What is a somatosatin analogue?

A

Octreotide - has a much longer half life thWhatan somatostatin. Won’t be broken down as quickly

56
Q

What is octreotide used for?

A

Treatment of GI tumours

57
Q

Where is secretin secreted from?

A

S cells of the upper duodenum and jejunum

58
Q

What causes the secretion of secretin?

A

Presence of acid in the duodenum (pH falls below 4.5)

59
Q

What is the function of secretin?

A

Stimulates pancreatic bicarbonate secretion (potentiated by CCK)
High concentrations of secretin inhibits gastric acid and gastric emptying

60
Q

Where is CCK secreted from?

A

Upper small intestine

61
Q

What stimulates the release of CCK?

A

Fat and peptides in the upper small intestine

62
Q

What is function of CCK?

A

Stimulates pancreatic enzyme release
Delays gastric emptying
Simulates gallbladder contraction
Decreases food intake and meal size

63
Q

Where is GIP secreted from?

A

Mucosal K cells in the duodenum and jejunum

64
Q

What does GIP stand for?

A

Gastric inhibitory polypeptide or glucose-dependent insulintropic peptide

65
Q

When is GIP released?

A

Following ingestion of a mixed meal

66
Q

What is the function of GIP?

A

Stimulates insulin secretion

67
Q

What happens if there are GIP receptor antagonists?

A

There is a reduced postprandial insulin release

68
Q

Where are PYY released?

A

Release from L cells throughout the muscosa of the terminal ileum, colon and rectum

69
Q

When is PYY released?

A

Postprandially

70
Q

What is the function of PYY?

A

Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion
It inhibits intestinal fluid and electrolyte secretion

71
Q

What is PYY3-36 do?

A

Inhibits food intake

Year 1: Alimentary System (15 decks)

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