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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
Where do the cell bodies of the preganglionic neurons of the parasympathetic system lie?
In the brainstem and sacral spinal cord.
26
Where do the cell bodies of the postganglionic neurones of the sympathetic neurons lie?
In the pre- and para vertebral ganglia
27
Where do the cell bodies of the postganglionic neurons of the parasympathetic system lie?
Close to target to organs - somtimes directly onto the enteric plexi
28
What innervates most of the GI tract down to the level of the transverse colon?
Vagus nerve
29
Where does the descending colon, sigmoid colon, rectum and anus receive parasympathetic fibres from?
Pelvic nerve
30
What neurotransmitter is used by parasympathetic system?
acetylcholine
31
How does the parasympathetic affect the GI tract?
Excitation
32
What two nerve plexuses make up the enteric nervous system?
Myenteric plexus and submucosal plexus
33
What structures do sympathetic fibres innervate?
The plexuses of the enteric nervous system but also directly on the blood vessels of the GI tract - to control vasocontriction
34
What does the enteric nervous system directly affect?
Smooth muscle Endocrine cells Secretory cells Blood vessels
35
What types of receptors exist on the GI tract wall?
Chemo and mechanoreceptors
36
What do receptors on the GI tract wall feedback to?
Local afferents - back to the enteric nervous system | Splanchnic and vagal afferents - back to the CNS
37
Where do endocrine cells exist in the gut?
Mucosa or submucosa of the stomach, intestine and pancreas
38
What hormones does the stomach secrete?
Gastrin Ghrelin Somatostatin Histamine
39
What hormones does the duodenum secrete?
Secretin CCK Somatostatin
40
What hormones does the jejunum and ileum secrete?
``` PYY GIP GLP-1 GLP-2 Oxyntomodulin Neurotensin Somatostatin ```
41
What hormones does the colon secrete?
``` PYY GLP-1 Oxyntonmodulin Neurotensin Somatostatin ```
42
What hormones does the pancreas secrete?
Insulin Glucagon Somatostatin Pancreatic polypeptide
43
Where are enteroendocrine cells found?
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
What can enteroendocrine cells sense?
Amino acids Fatty Acids Glucose
45
What is the function of the gastrointestinal endocrine system?
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
What is the effect of histamine in terms of paracrine effects?
Released from stomach walls - it stimulates HCl secretion by gastric parietal cells
47
What is the effect of somatostatin in terms of paracrine effects?
Released from the stomach - it inhibits acid secretion by paracrine mechanisms
48
Where is gastrin synthesised?
Gastric antrum and upper small intestine
49
What stimulates the release of gastrin?
aa and peptides Gastric distension Vagus nerve
50
What the function of gastrin?
Stimulates gastric acid secretion
51
What inhibits the release of gastrin?
When pH of the stomach falls below pH 3
52
Where is somatostatin synthesised?
All over the GI tract in endocrine D cells
53
What is the function of somatostatin?
Universal inhibitor of: gastric secretion, motility, intestinal and pancreatic secretions, release of gut hormones, intestinal nutrient and electrolyte transport, growth and proliferation
54
When is somatostatin released?
in response to a mixed meal
55
What is a somatosatin analogue?
Octreotide - has a much longer half life thWhatan somatostatin. Won't be broken down as quickly
56
What is octreotide used for?
Treatment of GI tumours
57
Where is secretin secreted from?
S cells of the upper duodenum and jejunum
58
What causes the secretion of secretin?
Presence of acid in the duodenum (pH falls below 4.5)
59
What is the function of secretin?
Stimulates pancreatic bicarbonate secretion (potentiated by CCK) High concentrations of secretin inhibits gastric acid and gastric emptying
60
Where is CCK secreted from?
Upper small intestine
61
What stimulates the release of CCK?
Fat and peptides in the upper small intestine
62
What is function of CCK?
Stimulates pancreatic enzyme release Delays gastric emptying Simulates gallbladder contraction Decreases food intake and meal size
63
Where is GIP secreted from?
Mucosal K cells in the duodenum and jejunum
64
What does GIP stand for?
Gastric inhibitory polypeptide or glucose-dependent insulintropic peptide
65
When is GIP released?
Following ingestion of a mixed meal
66
What is the function of GIP?
Stimulates insulin secretion
67
What happens if there are GIP receptor antagonists?
There is a reduced postprandial insulin release
68
Where are PYY released?
Release from L cells throughout the muscosa of the terminal ileum, colon and rectum
69
When is PYY released?
Postprandially
70
What is the function of PYY?
Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion It inhibits intestinal fluid and electrolyte secretion
71
What is PYY3-36 do?
Inhibits food intake

Year 1: Alimentary System (15 decks)

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