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
