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BRS Y1 > Week 11- Regulation of Gut Function > Flashcards

Week 11- Regulation of Gut Function Flashcards

1
Q

Where do sympathetic preganglionic neurons arise from?

A

Thoracic and lumbar spinal cord

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2
Q

What sympathetic nerves go to the stomach?

A

T6-9

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3
Q

What sympathetic nerves go to the colon?

A

L2-5

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4
Q

What postganglionic neurons innervate the stomach?

A

Coeliac ganglion

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5
Q

What postganglionic neurons innervate the small intestine?

A

Superior mesenteric ganglion

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6
Q

What postganglionic neurons innervate the colon?

A

Inferior mesenteric and pelvic ganglion

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7
Q

What neurotransmitter is involved with the sympathetic nervous system?

A

Norepinephrine

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8
Q

What does activation of sympathetic nervous system do to the activities of gastrointestinal tract?

A

Inhibit it

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9
Q

How is parasympathetic innervation to stomach, small

intestine and proximal colon supplied?

A

Vagus nerve

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10
Q

Where do parasympathetic preganglionic neurons originate?

A

Dorsal vagal complex within brainstem from sacral spinal

cord

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11
Q

What neurotransmitter is involved with the parasympathetic nervous system?

A

Acetylcholine

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12
Q

What does activation of parasympathetic nervous system

stimulate?

A

The GI tract

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13
Q

Describe the enteric (intrinsic) nervous system

A

Autonomous, can also interact with sympathetic and parasympathetic nervous system, the wall of the gastrointestinal tract contains many neurons

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14
Q

Where is the Meissner’s (submucosal) plexus found?

A

Submucosa

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15
Q

Where is the Auerbach’s (myenteric) plexus found?

A

Muscularis propria

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16
Q

Describe the Myenteric (Auerbach’s) plexus

A

Controls activity of muscularis externa
Controls gut motor (motility) function
Tone, velocity of contraction and intensity of
contraction.

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17
Q

Describe the Submucosal (Meissner’s) plexus

A

Senses the local environment (gut lumen)
Controls secretion, blood flow, epithelial and
endocrine cell function

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18
Q

What is the myenteric plexus known as?

A

Auerbach plexus

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19
Q

What is the submucosal plexus known as?

A

Meissner’s plexus

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20
Q

Describe the enteric nervous system local reflex

A

Food enters gut lumen and stretches the intestinal smooth muscles
Distension of the gut causes stimulation of the sensory neurons in the myenteric plexus
Chemicals in food stimulates sensory neurons in submucosal plexus
Sequential contraction/relaxation of circular and longitudinal muscle by inhibitory/excitatory neurotransmitter causes peristalsis, which allows food to
move along the GI tract

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21
Q

What do circular muscles do during peristalsis?

A

Contract behind the bolus of food

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22
Q

What do longitudinal muscles do during peristalsis?

A

Contract ahead of the bolus causing it to shorten and widen to receive the bolus

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23
Q

What does sympathetic stimulation of the enteric nervous system do to the gut?

A

Reduces peristalsis, absorption, secretion and blood flow

via enteric nervous system and also directly

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24
Q

What does parasympathetic stimulation of the enteric nervous system do to the gut?

A

Increases peristalsis, absorption, secretion, blood flow

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25
What is Hirschsprung’s disease? What is visible about the bowel for patients?
Congenital absence of ganglion of myenteric and submucosal Tonal contraction without reciprocal relaxation Intestinal distension proximal to ganglionic segment of bowel Most will require surgery The colon will be enlarged
26
What are the main endocrine gut hormones, what cells secrete them and where are they released?
Secreted by enteroendocrine cells Hormone released into bloodstream Main ones: gastrin, cholecystokinin, secretin, glucose-dependent insulinotropic peptide (GIP), motilin
27
What are the main paracrine gut hormones, where do they act?
Secreted by enteroendocrine cells Hormone that acts only within the vicinity that it is released Main ones: somatostatin and histamine
28
What hormones have both endocrine and paracrine mechanisms?
glucagon-like peptide-1 (GLP1), pancreatic polypeptide, and peptide YY
29
What are the main neurocrine gut hormones, what cells secrete them, what do they effect them and what are the main ones?
Secreted by postganglionic non-cholinergic neurons of the enteric nervous system Hormone that affects ‘nerves’ Main ones: vasoactive intestinal peptide (VIP), gastrin release peptide (GRP), and enkephalins
30
Where is gastrin secreted?
Gastric antrum and upper small intestine
31
What stimulates gastrin release?
Amino acids and peptides in the lumen of the stomach, gastric distension, vagus nerve
32
What does gastrin stimulate?
Gastric acid secretion by parietal cells in stomach
33
When is gastrin release inhibited?
When pH of stomach falls below pH 3
34
Where is secretin secreted?
By the S cells of the upper duodenum and jejunum
35
What stimulates secretin release?
Major stimulus is the presence of acid in the duodenum (pH falls below 4.5)
36
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
37
Where is cholecystokinin secreted?
Secreted by cells most densely located in the small intestine
38
What stimulates cholecystokinin release?
By fat and peptides in the upper small bowel
39
What is the function of cholecystokinin?
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
40
Where is glucose-dependent insulinotropic peptide (GIP) secreted?
By mucosal K cells (predominant in the duodenum and jejunum)
41
When is GIP released?
Following ingestion of a 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
42
What does GIP stimulate?
Insulin secretion
43
What is an example of a neuroendocrine tumour and describe it
Zollinger Ellison syndrome – tumour of gastric cells causing overproduction of gastrin and acid resulting in stomach and intestinal ulceration
44
How is Zollinger Ellison syndrome treated?
Treatment with proton pump inhibitor to inhibit | acid secretion, role for somatostatin analogues to halt tumour growth and reduce secretion
45
What is the role of motilin?
Increases gastrointestinal motility
46
Where is somatostatin synthesised?
In endocrine D cells of the gastric and duodenal mucosa, pancreas
47
When is somatostatin released?
in response to a mixed meal
48
What does somatostatin inhibit?
``` Gastric secretion Motility Intestinal and pancreatic secretions Release of gut hormones Intestinal nutrient and electrolyte transport Growth and proliferation ```
49
What is somatostatin?
A universal inhibitor
50
Where is GLP 1 produced?
In the small bowel and secreted from L cells
51
What stimulates GLP 1 release?
The presence of hexose and fat
52
What does GLP 1 induce?
Satiety and increases sensitivity of pancreatic beta-cells to glucose
53
What secretes pancreatic polypeptide?
PP cells in the pancreas
54
What stimulates the secretion of pancreatic polypeptide?
Stimulated by fat
55
What secretes peptide YY?
From cells found throughout the mucosa of the terminal ileum, colon and rectum, from L cells post- prandially (particularly protein)
56
What is the role of peptide YY?
Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion
57
What are the 3 main neurocrines?
VIP GRP Enkephalins
58
Where are neurocrines found?
Within nerves in the gut
59
What is the role of vasoactive intestinal peptide (VIP)?
Relaxation of gut smooth muscle
60
What is the role of gastrin releasing peptide (GRP)?
Induces gastrin release
61
What is the role of enkephalins?
Increases smooth muscle tone
62
Describe the role of the nervous system in the cephalic phase
Smell, thought, sight and taste of food and tactile sensations of food in the mouth stimulate brain stem Parasympathetic nervous system via the vagus nerves stimulate the enteric plexus Postganglionic neurons stimulate secretion of gastrin, acid (parietal cells) and digestive enzymes (chief cells) Gastrin released into bloodstream and induces secretion by parietal and chief cells
63
Describe the role of the nervous system in the gastric phase
Food arrives in stomach and distension causes signals via the vagus nerve to the brainstem This in turn stimulates stomach secretion Distension of the stomach and chemicals in food also activate the enteric nervous system to increase stomach secretion
64
How long does the gastric phase last?
3-4 hours
65
Describe the role of the nervous system in 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. Local reflexes activated by acid and lipids also act on the enteric nervous system to inhibit gastric secretions. Secretin, gastric inhibitory polypeptide and cholecystokinin, released by the duodenum inhibit gastric secretions.

BRS Y1 (52 decks)

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