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Gastroenterology > Regulation of Gut Function > Flashcards

Regulation of Gut Function Flashcards

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1
Q

What are the two parts of the nervous system involved in git function?

A

Autonomic (extrinsic)

Enteric (intrinsic)

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2
Q

What is the autonomic nervous system further divided into?

A

Sympathetic ‘fight and flight’

Parasympathetic ‘rest and digest’

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3
Q

Where does the sympathetic neurones come from?

A

Preganglionic neurons arise from the thoracic and lumbar spinal cord
Stomach (T6-9)
Colon (L2-5)

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4
Q

What terminates in ganglions?

A

Short pre-ganglionic axon

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5
Q

What are the important ganglions in the GI tract?

A

Stomach - coeliac ganglion
Small intestine – superior mesenteric ganglion
Colon – inferior mesenteric and pelvic ganglion

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6
Q

What sympathetic neurotransmitter is key in the GI tract?

A

Norepinephrine

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7
Q

What does the sympathetic nervous system do to the GI tract?

A

Inhibits GI function

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8
Q

What provides the parasympathetic innervation to the GI tract?

A

Vagus nerve

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9
Q

What is the structure of parasympathetic neurones in the GI tract?

A

Preganglionic neurons originate in dorsal vagal complex within brainstem from sacral spinal cord.

Long myelinated pre-ganglionic axons
Short un-myelinated post-ganglionic axons

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10
Q

What parasympathetic neurotransmitter is key in the GI tract?

A

Acetylcholine

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11
Q

What does activation of the parasympathetic nervous system do?

A

Stimulates the GI tract

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12
Q

What is the enteric nervous system?

A

2nd brain
functions autonomously
Interacts with autonomic nervous system
Resides within gut itself

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13
Q

What are the two plexus’ in the intrinsic nervous system?

A

Meissner’s (submucosal) plexus

Auberbach’s (myenteric) plexus

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14
Q

Where do you find Meissner’s plexus?

A

Submucosa

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15
Q

Where do you find Auberbach’s plexus?

A

In muscular propria

In-between circular and longitudinal muscle

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16
Q

What does the Meissner’s plexus do?

A
  • senses the local environment (gut lumen)
  • controls secretion, blood flow, epithelial and endocrine cell function
  • plays small role in motility of gut
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17
Q

What does Auberbach’s plexus do?

A
  • controls activity of muscularis externa
  • controls gut motor (motility) function
  • tone, velocity of contraction and intensity of contraction
  • responsible for peristalsis
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18
Q

Describe the first step of the local reflex of the enteric nervous system?

A

Food enters gut lumen and stretches the intestinal smooth muscles

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19
Q

Describe the second step of the local reflex of the enteric nervous system?

A

Distension of the gut causes stimulation of the sensory neurons in the myenteric plexus

Chemicals in food stimulates sensory neurons in submucosal plexus

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20
Q

Describe the third step of the local reflex of the enteric nervous system?

A

Sequential contraction/relaxation of circular and longitudinal muscle by inhibitory/excitatory neurotransmitter cause peristalsis, which allows food to move along the GI tract

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21
Q

What is peristalsis?

A

Wave of muscular contraction that moves the blows of food along the GI tract

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22
Q

What do the muscles behind bolus of food do in peristalsis?

A

Circular muscles behind food bolus contract

Longitudinal muscles behind food bolus relax and stretch

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23
Q

What do the muscles in front bolus of food do in peristalsis?

A

Circular relax

Longitudinal contract

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24
Q

How to the extrinsic and intrinsic nervous systems interact?

A

Feedback via sensory neurones from epithelium of gut to pre-vertebral ganglia, spinal cord and brainstem

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25
What are the overall effects of the sympathetic nervous system on the GI tract?
``` 'fight and flight’ reduces peristalsis reduces absorption reduces secretion reduces blood flow (via enteric nervous system and also directly) ```
26
What are the overall effects of the parasympathetic nervous system on the GI tract?
``` ‘rest and digest’ increases peristalsis increases absorption increases secretion increases blood flow ```
27
What is Hirschsprung's disease?
Congenital absence of ganglions of myenteric and submucosal plexus' Tonal contraction without reciprocal relaxation Intestinal distension proximal to aganglionic segment of bowel Most will require surgery
28
What are the three categories of gut-hormone?
Endocrine Paracrine Neurocrine
29
What are the main features of Endocrine hormones?
secreted by enteroendocrine cells | hormone released into bloodstream
30
What are the main features of paracrine hormones?
secreted by enteroendocrine cells hormone that acts only within the vicinity that it is released diffuses through extracellular space
31
What are the main features of neurocrine hormones?
secreted by postganglionic non-cholinergic neurons of the enteric nervous system hormone that affects ‘nerves’
32
Give example of endocrine hormones?
gastrin, cholecystokinin, secretin, glucose-dependent insulinotropic peptide (GIP), motilin
33
Give example of paracrine hormones?
somatostatin and histamine
34
Give example of neurocrine hormones?
vasoactive intestinal peptide (VIP), gastrin release peptide (GRP), and enkephalins
35
Where do you find enteroendocrine cells?
specialised epithelial cells located at the base of intestinal crypts throughout the GI tract, from stomach to colon
36
What are the function of enteroendocrine cells?
Possess hormone-containing granules concentrated at the basolateral membrane, adjacent to capillaries, that secrete their hormone in response to a wide range of stimuli
37
What stimulates enteroendocrine cells to secrete hormones?
small peptides, amino acids, fatty acids, oral glucose, distension of an organ, and vagal stimulation
38
What gut hormones are released in the stomach?
Gastrin Ghrelin Somatostatin Histamine
39
What gut hormones are released in the duodenum?
Secretin CCK Somatostatin
40
What gut hormones are released in the pancreas?
Insulin Glucagon Somatostatin Pancreatic Polypeptide
41
Where is gastrin synthesised?
gastric antrum and upper small intestine
42
What stimulates the release of gastrin?
amino acids and peptides in the lumen of the stomach gastric distension vagus nerve
43
What does gastrin stimulate?
gastric acid secretion by parietal cells in stomach
44
When is the release of gastrin inhibited?
when pH of stomach falls below pH 3
45
What effects can gastrin have?
Trophic (growth) effects on the mucosa of the small bowel, colon and stomach
46
What secreted secretin?
Secreted by the S cells of the upper duodenum and jejunum
47
What stimulates release of secretin?
Major stimulus is the presence of acid in the duodenum (pH falls below 4.5)
48
What is the function of secretin?
stimulates pancreatic bicarbonate secretion (effect potentiated by CCK) inhibition of gastric acid and gastric emptying inhibits gastrin, acid secretion, and growth of stomach mucosa stimulates biliary secretion of bicarbonate and fluid trophic effect on the exocrine pancreas
49
What secretes cholecystokinin (CCK)?
Secreted by cells most densely located in the small intestine
50
What stimulates release of CCK?
Release stimulated by fat and peptides in the upper small bowel
51
What is the function of CCK?
stimulates pancreatic enzyme release (lipase, amylase, proteases) delays gastric emptying stimulates gallbladder contraction and relaxation of the sphincter of Oddi decreases food intake and meal size trophic effects on the exocrine pancreas and gallbladder
52
What is GIP?
Glucose-dependent insulintropic peptide | a.k.a Gastic inhibitory peptide
53
What secreted GIP?
mucosal K cells (predominant in the duodenum and jejunum)
54
What stimulates release of GIP?
Ingestion of mixed meal The only hormone with a response to all 3 macronutrient types (glucose, amino acid, fatty acids) Likely stimulated by change in intraluminal osmolarity
55
What is the function of GIP?
Stimulates insulin secretion from pancreas
56
What is the function of motilin?
Increases GI motility
57
Where is somatostatin synthesised?
Synthesized in endocrine D cells of the gastric and duodenal mucosa, pancreas Released in response to meal
58
What is the function of somatostatin?
Somatostatin is a universal inhibitor (Endocrine Cyanide)
59
What does somatostatin inhibit?
``` gastric secretion motility intestinal and pancreatic secretions release of gut hormones intestinal nutrient and electrolyte transport growth and proliferation ```
60
Where is GLP-1 produced?
Small bowel and secreted from L cells
61
What stimulates release of GLP-1?
Presence of hexose and fat
62
What is the function of GLP-1?
Induces satiety | Increases sensitivity of pancreatic beta-cells to glucose
63
What cells secrete pancreatic polypeptide?
PP cells in the pancreas
64
What stimulates PP secretion?
Fat
65
What is the function of PP?
Potential role in satiety
66
What cells secrete peptide YY?
Secreted from cells found throughout the mucosa of the terminal ileum, colon and rectum Released from L cells post- prandially (particularly protein)
67
What is the function of peptide YY?
Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion
68
What are the three neurocrines active in the gut?
Vasoactive intestinal peptide (VIP) Gastrin releasing peptide (GRP) Enkephalins
69
What is the function of VIP?
relaxation of gut smooth muscle
70
What is the function of GRP?
Induces gastrin release
71
What is the function of enkephalins?
Increase smooth muscle tone
72
What are neuroendocrine tumours?
Tumours of the neuroendocrine cells (which are found predominantly in the gastrointestinal tract and pancreas) Does not behave like other cancers
73
What is Zollinger Ellison syndrome?
tumour of gastric cells causing overproduction of gastrin and acid resulting in stomach and intestinal ulceration - treatment with proton pump inhibitor to inhibit acid secretion - role for somatostatin analogues to halt tumour growth and reduce secretion
74
What are the three phases of gastric secretion?
Cephalic phase Gastric phase Intestinal phase
75
What is the cephalic phase (1)?
Smell, thought, sight and taste of food and tactile sensations of food in the mouth stimulate brain stem
76
What is the second step of the cephalic phase?
Parasympathetic nervous system via the vagus nerves stimulate the enteric plexus
77
What is the third step of the cephalic phase?
Postganglionic neurons stimulate secretion of gastrin, acid (parietal cells) and digestive enzymes (chief cells)
78
What is the fourth step of the cephalic phase?
Gastrin released into bloodstream and induces secretion by parietal and chief cells
79
What is the first step of the gastric phase?
This phase lasts 3-4 hours | Food arrives in stomach and distension causes signals via the vagus nerve to the brainstem
80
What is the second step of the gastric phase?
This in turn stimulates stomach secretion
81
What is the third step of the gastric phase?
Distension of the stomach and chemicals in food also activate the enteric nervous system to increase stomach secretion
82
What is the first step of the intestinal phase?
Chyme in the duodenum with pH<2 or lipids stimulate stretch and chemoreceptors that generate action potentials to the brainstem whereby they inhibit the parasympathetic nervous system, thereby inhibiting gastric secretions.
83
What is the second step of the intestinal phase?
Local reflexes activated by acid and lipids also act on the enteric nervous system to inhibit gastric secretions.
84
What is the third step of the intestinal phase?
Secretin, gastric inhibitory polypeptide and cholecystokinin, released by the duodenum inhibit gastric secretions.

Gastroenterology (12 decks)

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