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BRS Bioregulatory Systems > Regukation Of Gut Function > Flashcards

Regukation Of Gut Function Flashcards

1
Q

What are the 2 components to the gut nervous system?

A
  • Autonomic (extrinsic) NS → made of sympathetic and parasympathetic NS
  • Enteric (intrinsic) NS
  • They work independently of each other but can work together
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2
Q

Where do the preganglionic neurones arise from?s

A
  • Thoracic and lumbar spinal cord
  • Stomach is supplied by T6-9 neurones
  • Colon is supplied by L2-5 neurones
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3
Q

Which postganglionic neurones innervate which parts of the GI system?s

A
  • Stomach supplied by coeliac ganglion
  • Small intestine supplied by superior mesenteric ganglion
  • Colon supplied by inferior mesenteric and pelvic ganglion
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4
Q

What neurotransmitter is used in the sympathetic NS?

A

Norepinephrine (noradrenaline)

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5
Q

What does activation of sympathetic NS do to GI tract?

A

Inhibits its activities

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6
Q

What nerve gives parasympathetic innervation to stomach, small bowel and proximal colon?

A

Vagus

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7
Q

Where do the preganglionic neurones originate?

A
  • Dorsal vagal complex in brainstem
  • Also originate separately from sacral spinal cord
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8
Q

What NT do the postganglionic neurones use?

A

Ach

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9
Q

What does the parasympathetic NS do to the GI tract?

A

Stimulates its activity

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10
Q

Enteric nervous system

A
  • The second brain
  • It’s autonomous but can interact with SN and para NS
  • The walls of the GI tract have the enteric NS neurones as the myenteric and submucosal plexuses
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11
Q

What and where are the 2 plexuses?

A
  • Meissner’s (submucosal) plexus
  • Auerbach’s (myenteric) plexus → lies between circular and longitudinal muscles
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12
Q

What does the submucosal plexus do?

A
  • Senses local environment in gut lumen
  • Controls secretion, blood flow, epithelial and endocrine cell function
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13
Q

What does the myenteric plexus do?

A
  • controls activity of muscularis propria
  • Controls gut motor (motility) function
  • Controls tone, velocity of contraction and intensity of contraction
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14
Q
  • Describe the local reflex of the enteric NS when food enters the gut lumen
A

1) Food enters gut lumen and stretches intestinal smooth muscles

2) Distension of the gut stimulates the sensory neurones in the myenteric plexus

3) This coordinates a peristaltic wave by sequential contraction/relaxation of circular and longitudinal muscle by inhibitory/excitatory NTs- moves food through gut

4) Chemicals in the food also stimulate sensory neurones in the submucosal plexus which stimulates release of gut secretions and increases local blood flow to promote digestion and nutrient absorption

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15
Q

What are the sympathetic NS effects on enteric NS? (4)

A

Inhibits digestion

  • Reduces peristalsis
  • Reduces absorption
  • Reduces secretion
  • Reduces blood flow (via enteric NS and also directly)
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16
Q

What are the parasympathetic NS effects on enteric NS? (4)

A

Promotes digestion

  • Increases peristalsis
  • Increases absorption
  • Increases secretion
  • Increases blood flow
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17
Q

What is Hirschsprung’s Disease?

A
  • commonest cause of neonatal bowel obstruction
  • Congenital absence of ganglion of myenteric and submucosal plexus
  • Tonal contraction without reciprocal relaxation
  • Faeces accumulates and can’t be passed as stool due to failure to relax muscle
  • Here, affected rectum remains contracted and so left side of bowel dilates
  • Standard management is resection of affected segment- surgery usually takes place at 6-12 months
18
Q

What are endocrine hormones + secreted by what?

A

Secreted by enteroendocrine cells
Secretin
Motilin
Gastrin
Cholecystokinin
Glucose dependant insulinotropic peptide

19
Q

Secretin

A
  • Secreted by S cells of upper duodenum and jejunum
  • Major stimulus is presence of acid in duodenum- when pH falls below 4.5
  • Stimulates pancreatic bicarbonate secretion (effect potentiated by CCK)
  • Inhibition of gastric acid and gastric emptying
  • Inhibits gastrin, acid secretion & growth of stomach mucosa
  • Stimulates biliary secretion of bicarbonate and fluid
  • Trophic effect on the exocrine pancreas
20
Q

Motilin

A

Released in proximal small bowel
Increases gastrointestinal motility

21
Q

Gastrin

A
  • Synthesised in gastric antrum and upper small intestine by G cells
  • Release stimulated by amino acids + peptides in stomach lumen, gastric distension and the vagus nerve
    It stimulates gastric acid secretion by parietal cells in stomach
    Inhibited by low pH
22
Q

Glucose-dependent insulinotropic peptide (GIP) aka gastric inhibitory polypeptide

A

Secreted by Mucosal K cells predominant in duodenum and jejunum and is released following ingestion of a mixed meal

Likely stimulated by change in intraluminal osmolarity

It’s the only hormone with a response to all three macronutrient types eg glucose amino acids and fatty acids

It stimulates insulin secretion and decreases gastric acid release

23
Q

Cholecystokinin

A
  • Secreted by I cells most densely located in the small bowel
  • Release stimulated by fat & peptides in the upper small bowel
  • stimulates pancreatic enzyme release (lipase, amylase, proteases)
  • stimulates gallbladder contraction and relaxation of the sphincter of Oddi
  • delays gastric emptying
  • decreases food intake and meal size
  • trophic effects on exocrine pancreas and gallbladder
24
Q

What are paracrine hormones + secreted by what?

A
  • Hormone that acts only within vicinity its released in- diffuses through extracellular space
  • Secreted by enteroendocrine cells
    Eg somatostatin and histamine
25
Q

Somatostatin

A
  • Synthesised in endocrine D cells of gastric and duodenal mucosa & pancreas
  • Release in response to a mixed meal- fat, glucose, bile salts

It’s a universal inhibitor (endocrine cyanide). It inhibits:

  • gastric (acid) secretion
  • motility
  • intestinal and pancreatic secretions
  • release of gut hormones
  • intestinal nutrient and electrolyte transport
  • growth and proliferation
26
Q

Which hormones have both endocrine and paracrine mechanisms?

A

Glucagon like peptide
Pancreatic polypeptide
Peptide YY aka peptide tyrosine tyrosine

27
Q

GLP-1

A
  • Produced and secreted from L cells in small bowel
  • Release stimulated by presence of hexose and fat
  • Induces satiety
  • Increases sensitivity of pancreatic beta cells to glucose (thereby stimulate insulin secretion), also inhibits glucagon
28
Q

Pancreatic polypeptide

A

Secreted by pancreatic polypeptide (PP) cells in pancreas

Secretion stimulated by fat

Potential role in satiety

29
Q

Peptide tyrosine tyrosine

A

Secreted by L cells in mucosa of terminal ileum,colon,rectum post prandially

  • Reduces intestinal motility
  • Reduces gallbladder contraction
  • Reduces pancreatic exocrine secretion
30
Q

What are neurocrine hormones + secreted by what?

A
  • Hormone that affects nerves
  • Secreted by postganglionic non-cholinergic neurones of the enteric nervous system
31
Q

Examples of neurocrine hormones

A
  • Vasoactive intestinal peptide (VIP)- what does it do?Relaxes gut smooth muscle and stimulates pancreatic secretions
  • Gastrin release peptide (GRP)- what does it do?Induces gastrin release
  • Enkephalins- what do they do?Act on opioid receptors in gut and inhibit peristalsis by increasing smooth muscle tone in gut
32
Q

Enteroendocrine cells

A
  • Specialised epithelial cells in base of intestinal crypts through GI tract from stomach to colon
  • Have hormone-containing granules concentrated at basolateral membrane next to capillaries that secrete hormone in response to many stimuli

Stimuli include small peptides amino acids fatty acids oral glucose distension of an organ and vagal stimulation

33
Q

Enteroendocrine cell types

A

K cells
I cells
L cells

34
Q

Hormones released by stomach

A
  • Gastrin
  • Ghrelin
  • Somatostatin
  • Histamine
35
Q

Duodenum

A
  • Secretin
  • CCK
  • Somatostatin
36
Q

Pancreas

A
  • Insulin
  • Glucagon
  • Somatostatin
  • Pancreatic polypeptide
37
Q

Small bowel

A
  • Peptide YY
  • GIP
  • GLP-1 and GLP-2
  • Oxyntomodulin
  • Neurotensin
  • Somatostatin
38
Q

Large bowel

A
  • Peptide YY
  • GLP-1
  • Oxyntomodulin
  • Neurotensin
  • Somatostatin
39
Q

Neuroendocrine tumours

A

Tumours of neuroendocrine cells which are predominantly found in GI tract and pancreas

Most (60%) originate in GI tract but 20-30% originate in lungs and 15% in skin/thymus/other places

40
Q

Zollinger Ellison syndrome

A

Gastrinoma- tumour of gastric cells causes overproduction of gastrin and acid resulting in stomach and intestinal ulceration

  • Treatment with proton pump inhibitors like Omeprazole which inhibits acid secretion
  • Somatostatin analogues that mimic somatostatin to halt tumour growth and reduce secretion

BRS Bioregulatory Systems (54 decks)

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