Regulation of gut function (42) Flashcards
How is the gut nervous system divided?
- autonomic/extrinsic–> sympathetic + parasympathetic
- enteric/intrinsic
Where do the sympathetic preganglionic neurones that supply the gut arise from in the spinal cord?
thoracolumbar region
stomach: T6-9
colon: L2-5
What ganglion does the supply to the stomach come from?
coeliac
What ganglion does the supply to the small intestine come from?
superior mesenteric
What ganglion does the supply to the colon come from?
inferior mesenteric and pelvic
What is the main neurotransmitter involved in the sympathetic nervous system supply to the gut?
norepinephrine
What happens to the GI tract when the sympathetic nervous system is activated?
activities are inhibited
What is the parasympathetic innervation to the GI tract and where do the preganglionic neurons originate?
- vagus nerve supplies stomach, small intestine and proximal colon
- pelvic nerve supplies distal colon
- preganglionic neurons originate in dorsal vagal complex (vagal nerves) within brainstem and from sacral spinal cord (pelvic nerves)
What is the main neurotransmitter involved in the parasympathetic nervous system supply to the gut?
acetylcholine
What happens to the GI tract when the parasympathetic nervous system is activated?
GI tract is stimulated
What is the difference between the placement of the ganglia in the sympathetic and parasympathetic nervous systems?
- sympathetic ganglia = near spinal cord, so short preganglionic axons
- parasympathetic ganglia = near target organ, so long preganglionic axons
What is a plexus?
a network of intersecting nerves
Where is the submucosal plexus located?
in submucosal layer of the GI tract
Where is the myenteric plexus located?
in between the circular muscle layer (inner) and longitudinal muscle layer (outer)
What is the function of the submucosal plexus?
- senses the local environment in the gut lumen e.g. change in pH
- controls secretion, blood flow, epithelial and endocrine cell function
What is the function of the myenteric plexus?
- controls activity of muscularis externa
- senses stretch
- controls gut motor function: tone, velocity and intensity of contraction
How does peristalsis work?
- wave of muscular contractions moves the bolus through the small intestine
- circular and longitudinal muscles work in opposite ways–> 1 contracts while the other relaxes
- circular muscles contract behind bolus of food
- longitudinal muscles ahead bolus contract, whereas behind relax
What is Hirschsprung’s disease?
- congenital absence of myenteric and submucosal ganglions
- tonal contraction without reciprocal relaxation
- enlarged colon
- most require surgery
What are endocrine gut hormones?
- secreted by enteroendocrine cells
- hormones released into bloodstream
- gastrin, CCK, secretin, GIP, motilin
What are paracrine gut hormones?
- secreted by enteroendocrine cells
- hormone that acts only within its vicinity
- diffuses through extracellular space
- somatostatin, histamine
What are neurocrine gut hormones?
- secreted by postganglionic non-cholinergic neurons of enteric nervous system
- affects ‘nerves’
- vasoactive intestinal peptide (VIP), gastrin release peptide (GRP) and enkephalins
What hormones use both endocrine and paracrine mechanisms?
GLP-1, pancreatic polypeptide and peptide YY
What are enteroendocrine cells?
- specialised epithelial cells located at base of intestinal crypts throughout GI tract (stomach–>colon)
- have granules at basolateral membrane, adjacent to capillaries, that secrete hormone in response to stimuli: small peptides, AAs, fatty acids, glucose, organ distention and vagal stimulation
What gut hormones are released in the stomach?
- gastrin
- ghrelin
- somatostatin
- histamine
What gut hormones are released in the duodenum?
- CCK
- secretin
- somatostatin
What gut hormones are released in the pancreas?
- insulin
- glucagon
- somatostatin
- pancreatic polypeptide
What gut hormones are released in the 2nd bit of the small bowel?
- PYY
- GIP (gastric inhibitory peptide)
- GLP-1
- GLP-2
- oxyntomodulin
- neurotensin
- somatostatin
What gut hormones are released in the large bowel?
- PYY
- GLP-1
- oxyntomodulin
- neurotensin
- somatostatin
What is gastrin?
- hormone synthesised in gastric antrum and upper small intestine
- released stimulated by AAs, peptides, gastric distension and vagus nerve (parasymp)
- stimulates parietal cells to secrete acid
- release inhibited when pH in stomach <3
What is secretin?
- hormone secreted by S cells in upper duodenum and jejunum
- release stimulated by presence of acid in duodenum
- stimulates pancreatic bicarbonate secretion
- inhibits gastrin, acid secretion, and growth of stomach mucosa
What is cholecystokinin?
- hormone secreted by duodenal I-cells
- release stimulated by fat and peptides in upper small bowel
- stimulates pancreatic enzyme release (lipase, amylase, proteases)
- delays gastric emptying
- stimulates gallbladder contraction and relaxes sphincter of Oddi
- hunger suppressant
What is glucose-dependent insulinotropic peptide (GIP)?
- hormones secreted by K cells in small bowel
- release stimulated by all 3 macronutrients: glucose, AAs, fatty acids
- stimulates release of insulin from pancreas
What is the function of the hormone motilin?
increases GI motility
What is somatostatin?
- hormone secreted by D cells in stomach, intestine and pancreas
- universal inhibitor
- stops gastric secretion, release of gut hormones etc…
What is glucagon-like peptide-1 (GLP-1)?
- hormone secreted in small bowel from L cells
- release stimulated by presence of glucose and fat
- induces satiety and increases sensitivity of pancreatic beta cells to glucose
What is pancreatic polypeptide?
- hormone secreted by PP cells in pancreas
- release stimulated by fat
- potential role in satiety
What is peptide YY?
- hormone secreted by L cells after meal
- reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion
Where are the neurocrines located?
within nerves in the gut
What is the function of vasoactive intestinal peptide (VIP)?
relaxation of gut smooth muscle
What is the function of gastrin releasing peptide (GRP)?
induces gastrin release
What is the function of enkephalins?
increase smooth muscle tone
What are neuroendocrine tumours?
proliferation of neuroendocrine cells in GI tract and pancreas
