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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
Q

What is Hirschsprung’s disease? What is visible about the bowel for patients?

A

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

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26
Q

What are the main endocrine gut hormones, what cells secrete them and where are they released?

A

Secreted by enteroendocrine cells
Hormone released into bloodstream
Main ones: gastrin, cholecystokinin, secretin, glucose-dependent insulinotropic peptide (GIP), motilin

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27
Q

What are the main paracrine gut hormones, where do they act?

A

Secreted by enteroendocrine cells
Hormone that acts only within the vicinity that it is released
Main ones: somatostatin and histamine

28
Q

What hormones have both endocrine and paracrine mechanisms?

A

glucagon-like peptide-1 (GLP1), pancreatic polypeptide, and peptide YY

29
Q

What are the main neurocrine gut hormones, what cells secrete them, what do they effect them and what are the main ones?

A

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
Q

Where is gastrin secreted?

A

Gastric antrum and upper small intestine

31
Q

What stimulates gastrin release?

A

Amino acids and peptides in the lumen of the stomach, gastric distension, vagus nerve

32
Q

What does gastrin stimulate?

A

Gastric acid secretion by parietal cells in stomach

33
Q

When is gastrin release inhibited?

A

When pH of stomach falls below pH 3

34
Q

Where is secretin secreted?

A

By the S cells of the upper duodenum and jejunum

35
Q

What stimulates secretin release?

A

Major stimulus is the presence of acid in the duodenum (pH falls below 4.5)

36
Q

What is the function of secretin?

A

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
Q

Where is cholecystokinin secreted?

A

Secreted by cells most densely located in the small intestine

38
Q

What stimulates cholecystokinin release?

A

By fat and peptides in the upper small bowel

39
Q

What is the function of cholecystokinin?

A

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
Q

Where is glucose-dependent insulinotropic peptide (GIP) secreted?

A

By mucosal K cells (predominant in the duodenum and jejunum)

41
Q

When is GIP released?

A

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
Q

What does GIP stimulate?

A

Insulin secretion

43
Q

What is an example of a neuroendocrine tumour and describe it

A

Zollinger Ellison syndrome – tumour of
gastric cells causing overproduction of gastrin and acid
resulting in stomach and intestinal ulceration

44
Q

How is Zollinger Ellison syndrome treated?

A

Treatment with proton pump inhibitor to inhibit

acid secretion, role for somatostatin analogues to halt tumour growth and reduce secretion

45
Q

What is the role of motilin?

A

Increases gastrointestinal motility

46
Q

Where is somatostatin synthesised?

A

In endocrine D cells of the gastric and duodenal mucosa, pancreas

47
Q

When is somatostatin released?

A

in response to a mixed meal

48
Q

What does somatostatin inhibit?

A 
Gastric secretion
Motility
Intestinal and pancreatic secretions
Release of gut hormones
Intestinal nutrient and electrolyte transport
Growth and proliferation
49
Q

What is somatostatin?

A

A universal inhibitor

50
Q

Where is GLP 1 produced?

A

In the small bowel and secreted from L cells

51
Q

What stimulates GLP 1 release?

A

The presence of hexose and fat

52
Q

What does GLP 1 induce?

A

Satiety and increases sensitivity of pancreatic beta-cells to glucose

53
Q

What secretes pancreatic polypeptide?

A

PP cells in the pancreas

54
Q

What stimulates the secretion of pancreatic polypeptide?

A

Stimulated by fat

55
Q

What secretes peptide YY?

A

From cells found throughout the mucosa of the terminal ileum, colon and rectum, from L cells post- prandially (particularly protein)

56
Q

What is the role of peptide YY?

A

Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion

57
Q

What are the 3 main neurocrines?

A

VIP
GRP
Enkephalins

58
Q

Where are neurocrines found?

A

Within nerves in the gut

59
Q

What is the role of vasoactive intestinal peptide (VIP)?

A

Relaxation of gut smooth muscle

60
Q

What is the role of gastrin releasing peptide (GRP)?

A

Induces gastrin release

61
Q

What is the role of enkephalins?

A

Increases smooth muscle tone

62
Q

Describe the role of the nervous system in the cephalic phase

A

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
Q

Describe the role of the nervous system in the gastric phase

A

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
Q

How long does the gastric phase last?

A

3-4 hours

65
Q

Describe the role of the nervous system in the intestinal phase?

A

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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