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2.8 BRS Gastroenterology > Regulation of Gut > Flashcards

Regulation of Gut Flashcards

1
Q

How does the SNS control gut function?

A

Inhibits digestion (NA)
Preganglionic - stomach —> T6-9
- colon —> L2-5
Postganglionic - stomach —> coecliac ganglion
- small bowel —> superior mesenteric
- colon —> inferior mesenteric + pelvic

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2
Q

What are the 2 nervous controls of gut function?

A
  1. ANS
  2. Enteric nervous system
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3
Q

How does the PNS control gut function?

A

Stimulates digestion (ACh)
Preganglionic - stomach, small bowel, proximal colon
—> vagus (dorsal vagal complex)
- distal colon —> sacral spinal cord
Postganglionic - stomach, small bowel, proximal colon
—> vagal nerves
- distal colon —> pelvic nerves

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4
Q

How does the enteric nervous system control gut function?

A

Submucosal plexus —> submucosa
- senses gut lumen environment
(distension and food chemicals)
- controls secretions, blood flow,
epithelial/endothelial function

Myenteric plexus —> muscularis propria
- controls gut motility (contraction
velocity and intensity)

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5
Q

How does peristalsis occur?

A

Circular muscles behind contract
Longitudinal muscles in front contract

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6
Q

What is Hirschsprung’s Disease?

A

Congenital absence of myenteric and submucosal ganglion
- contractions without relaxation
- intestinal distension near issue —> resected

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7
Q

What are the 3 hormonal controls of gut function?

A
  1. Endocrine —> hormone to bloodstream
    - secretion via enteroendocrine cells
  2. Paracrine —> hormone only acts where released
    via diffusion
    - secretion via eneteroendocrine cells
  3. Neurocrine —> hormone affects nerves
    - secretion via enteric postganglionic
    non-cholinergic neurones
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8
Q

What are enteroendocrine cells?

A

Specialised epithelial cells at base of intestinal crypts
- hormone-containing granules (basolateral) —>
secreted into bloodstream

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9
Q

How does endocrine control of the gut occur? (5)

A
  1. Gastrin
  2. Cholecystokinin
  3. Secretin
  4. GIP (gastric inhibitory peptide)
  5. Motilin
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10
Q

How does paracrine control of the gut occur? (5)

A
  1. Somatostatin
  2. Histamine
  3. GLP-1
  4. Pancreatic polypeptide
  5. Peptide YY
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11
Q

How does neurocrine control of the gut occur?

A
  1. VIP (vasoactive intestinal peptide)
  2. GRP (gastrin release peptide)
  3. Enkephalins
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12
Q

Which 5 regions of the GI tract secrete hormones?

A
  1. Stomach —> gastrin
    —> ghrelin
    —> somatostatin
    —> histamine
  2. Pancreas —> insulin
    —> glucagon
    —> pancreatic polypeptide
    —> somatostatin
  3. Duodenum —> secretin
    —> CCK
    —> somatostatin
  4. Jejunum —> PYY
    —> GIP
    —> GLP-1
    —> GLP-2
    —> oxyntomodulin
    —> neurotensin
    —> somatostatin
  5. Ileum —> PYY
    —> GLP-1
    —> oxyntomodulin
    —> neurotensin
    —> somatostatin
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13
Q

What is gastrin?

A

Function:
Stimulate gastric acid secretion by parietal cells

Secretion:
- gastric antrum
- upper small intestine

Stimulus:
- amino acids and peptides in stomach
- gastric distension
- vagus nerve

Inhibition:
- stomach pH < 3

Effects:
- inc gastrin secretion
- growth of mucosal layer

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14
Q

What is secretin?

A

Function:
Neutralise gastric acid (pancreatic bicarbonate)

Secretion:
- S cells of duodenum and jejunum

Stimulus:
- stomach pH < 4.5

Effects:
- stimulates —> pancreatic bicarbonate secretion
—> biliary bicarbonate and fluid secretion
- inhibits —> gastrin secretion
—> gastric emptying
- growth of exocrine pancreas

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15
Q

What is cholecystokinin?

A

Function:
Pancreatic enzyme and gallbladder bile secretion

Secretion:
- small bowel cells

Stimulus:
- fats and peptides in upper small intestine

Effects:
- stimulates —> pancreatic enzyme release
—> gallbladder contraction
—> sphincter of Oddi relaxation
- inhibits —> gastric emptying (delay)
—> food intake
- growth of exocrine pancreas and gallbladder

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16
Q

What is GIP?

A

Function:
Stimulates insulin secretion

Secretion:
- K cells of duodenum and jejunum (mucosal)

Stimulus:
- ingestion of glucose, amino acids and fatty acids —>
changes intraluminal osmolarity

17
Q

What is motilin?

A

Function:
Increase gastrointestinal motility

Stimulus:
- food ingested

18
Q

What is somatostatin?

A

Function:
Universal inhibitor

Secretion:
- D cells in gastric mucosa, duodenal mucosa,
pancreas

Stimulus:
- ingestion of glucose, amino acids and fatty acids —>

Effects:
- inhibits —> gastric, intestinal, pancreatic secretions
—> motility
—> gut hormone release
—> intestinal nutrient/electrolyte transport
—> growth and proliferation

19
Q

What is GLP-1?

A

Function:
Satiety

Secretion:
- L cells of small intestine

Stimulus:
- hexose and fat

Effects:
- inc β-cell sensitivity to glucose

20
Q

What is pancreatic polypeptide?

A

Function:
Satiety

Secretion:
- PP cells of pancreas

Stimulus:
- fat

21
Q

What is peptide YY?

A

Function:
Dec intestinal motility, galbladder contractions, pancreatic exocrine secretions

Secretion:
- L cells of terminal ileum, colon, rectum mucosa

Stimulus:
- meal eaten (especially protein)

22
Q

What is VIP?

A

Function:
Relaxation of gut smooth muscles

23
Q

What is GRP?

A

Function:
Induce gastrin release

24
Q

What are enkephalins?

A

Function:
Increase smooth muscle tone

25
Q

What is Zollinger Ellison syndrome?

A

Gastric cell tumour
—> overproduction of gastric acid
- treatment —> proton pump inhibitor
—> somatostatin analogues

26
Q

What are the 3 phases of gastric secretion?

A
  1. Cephalic
  2. Gastric
  3. Intestinal
27
Q

What is the cephalic phase?

A

Preparation for digestion
1. Food seen, smelt, tasted etc. —> stimulate
brainstem
2. PNS stimulate enteric plexus via vagus nerve
3. Inc gastrin secretion —> inc gastric acid secretion
—> inc enzyme secretion

28
Q

What is the gastric phase?

A

Bolus enters stomach
1. Distension of stomach —> sensed by vagus nerve
2. Inc stomach secretion
Activate enteric nervous system
- lasts 3-4 hrs

29
Q

What is the intestinal phase?

A

Chyme enters duodenum
1. Chyme pH < 2 and lipids enter —> stretch and
chemoreceptors —> brainstem
2. PNS inhibited
Enteric nervous system activated —> secretin, GIP,
cholecystokinin secreted by duodenum
3. Gastric secretions inhibited

2.8 BRS Gastroenterology (13 decks)

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