Regulation of Gut Flashcards
(29 cards)
How does the SNS control gut function?
Inhibits digestion (NA)
Preganglionic - stomach —> T6-9
- colon —> L2-5
Postganglionic - stomach —> coecliac ganglion
- small bowel —> superior mesenteric
- colon —> inferior mesenteric + pelvic
What are the 2 nervous controls of gut function?
- ANS
- Enteric nervous system
How does the PNS control gut function?
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
How does the enteric nervous system control gut function?
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)
How does peristalsis occur?
Circular muscles behind contract
Longitudinal muscles in front contract
What is Hirschsprung’s Disease?
Congenital absence of myenteric and submucosal ganglion
- contractions without relaxation
- intestinal distension near issue —> resected
What are the 3 hormonal controls of gut function?
- Endocrine —> hormone to bloodstream
- secretion via enteroendocrine cells - Paracrine —> hormone only acts where released
via diffusion
- secretion via eneteroendocrine cells - Neurocrine —> hormone affects nerves
- secretion via enteric postganglionic
non-cholinergic neurones
What are enteroendocrine cells?
Specialised epithelial cells at base of intestinal crypts
- hormone-containing granules (basolateral) —>
secreted into bloodstream
How does endocrine control of the gut occur? (5)
- Gastrin
- Cholecystokinin
- Secretin
- GIP (gastric inhibitory peptide)
- Motilin
How does paracrine control of the gut occur? (5)
- Somatostatin
- Histamine
- GLP-1
- Pancreatic polypeptide
- Peptide YY
How does neurocrine control of the gut occur?
- VIP (vasoactive intestinal peptide)
- GRP (gastrin release peptide)
- Enkephalins
Which 5 regions of the GI tract secrete hormones?
- Stomach —> gastrin
—> ghrelin
—> somatostatin
—> histamine - Pancreas —> insulin
—> glucagon
—> pancreatic polypeptide
—> somatostatin - Duodenum —> secretin
—> CCK
—> somatostatin - Jejunum —> PYY
—> GIP
—> GLP-1
—> GLP-2
—> oxyntomodulin
—> neurotensin
—> somatostatin - Ileum —> PYY
—> GLP-1
—> oxyntomodulin
—> neurotensin
—> somatostatin
What is gastrin?
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
What is secretin?
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
What is cholecystokinin?
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
What is GIP?
Function:
Stimulates insulin secretion
Secretion:
- K cells of duodenum and jejunum (mucosal)
Stimulus:
- ingestion of glucose, amino acids and fatty acids —>
changes intraluminal osmolarity
What is motilin?
Function:
Increase gastrointestinal motility
Stimulus:
- food ingested
What is somatostatin?
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
What is GLP-1?
Function:
Satiety
Secretion:
- L cells of small intestine
Stimulus:
- hexose and fat
Effects:
- inc β-cell sensitivity to glucose
What is pancreatic polypeptide?
Function:
Satiety
Secretion:
- PP cells of pancreas
Stimulus:
- fat
What is peptide YY?
Function:
Dec intestinal motility, galbladder contractions, pancreatic exocrine secretions
Secretion:
- L cells of terminal ileum, colon, rectum mucosa
Stimulus:
- meal eaten (especially protein)
What is VIP?
Function:
Relaxation of gut smooth muscles
What is GRP?
Function:
Induce gastrin release
What are enkephalins?
Function:
Increase smooth muscle tone
