Regulation of Gut Function and Appetite Flashcards
(52 cards)
How is the gut nervous system divided?
Gut nervous system is made up of the autonomic (extrinsic) and enteric (intrinsic) nervous system
The autonomic nervous system can be further divided into the sympathetic (fight or flight) and parasympathetic (rest and digest)
Where do the sympathetic nerves arise from?
Sympathetic preganglionic neurons arise from the thoracic and lumbar spinal cord:
Stomach: T6-9
Colon: L2-5
Preganglionic nerves innervating:
Stomach- coeliac ganglion
Small Intestine- superior mesenteric ganglion
Colon- inferior mesenteric and pelvic ganglion
What post-ganglionic neurotransmitter is involved in the sympathetic nervous system?
The neurotransmitter is norepinephrine (noradrenaline)
What is the role of the sympathetic nervous system?
It inhibits activities of the GI tract
What does the parasympathetic system innervate?
Innervates the stomach, small intestine and proximal colon
What supplies the parasympathetic system?
The vagus nerve
Where do parasympathetic nerves arise from?
Preganglionic neurons originate in dorsal vagal complex within brainstem in the medulla and from sacral spinal cord
What is the post-ganglionic neurotransmitter in the parasympathetic nervous system?
Acetylcholine
What is the role of the parasympathetic nervous system?
Stimulates the GI tract
Where do sympathetic and parasympathetic pre- ganglia synapse with post-ganglia?
Sympathetic: Near spinal cord in a row
Parasympathetic: Near target organ
How do fibre lengths for sympathetic and parasympathetic ganglia compare?
Sympathetic: short preganglionic fibre, long postganglionic fibre
Parasympathetic: Long preganglionic, short postganglionic
What is the enteric nervous system?
Intrinsic nervous system
“2nd brain”
Autonomous- Has intrinsic microcircuits to carry out GI functions independent of the brain and spinal cord
Can interact with SNS and PNS
Wall of GI tract contains many neurons in the myenteric plexus and submucosal plexus
How is the gut structured?
Innermost first:
Mucosa:
epithelium
lamina propria
muscularis mucosa
Submucosal:
meissner’s (submucosal) plexus- inner plexus
Muscularis Propria:
circular muscle
auerbach’s (myenteric) plexus (outer plexus)
longitudinal muscle
Serosa or adventitia
Has mainly control over GI movements- motility of bowel wall
What is the function of the myenteric (Auerbach’s) plexus?
Controls activity of muscularis propria
Controls gut motor (motility) function
Mediates tone, velocity of contraction and intensity of contraction
What is the function of the submucosal (meissner’s plexus)?
senses the local environment (gut lumen)
controls secretion, blood flow, epithelial and endocrine cell function and alters electrolyte and water transport
How does the enteric nervous system bring about a local reflex?
Food enters gut lumen and stretches the intestinal smooth muscle
Distension of the gut causes stimulation of the sensory neurons in the myenteric plexus
Chemicals in the food stimulate sensory neurones in submucosal plexus
This causes coordination of a peristaltic wave by contracting the smooth muscle behind the bolus and relaxing the smooth muscle in front of the bolus to push it forward- this is controlled by excitatory and inhibitory neurotransmitters
How does peristalsis happen?
Circular muscles contract behind the bolus of food
Longitudinal muscles contract ahead of the bolus causing it to shorten and widen to receive bolus
Circular and longitudinal muscles work antagonistically
What does activation of the sympathetic nervous system lead to?
reduces peristalsis
reduces absorption
reduces secretion
reduces blood flow (via enteric nervous system and directly)
What does activation of the parasympathetic nervous system lead to?
Increased peristalsis
Increased absorption
Increased secretion
Increased blood flow
What is Hirschsprung’s disease?
Congenital absence of ganglion of myenteric and submucosal
Tonal contraction without reciprocal relaxation- affected part of the bowel remains contracted
Intestinal distention proximal to aganglionic segment of bowel - the unaffected part is distended
Most will require surgery (usually carried out at 6-12 months old)
What are endocrine hormones?
Secreted by enteroendocrine cells
Hormone released into bloodstream
E.g. gastrin, cholecystokinin, secretin, glucose-dependent insulinotropic polypeptide (GIP), motilin
What is paracrine hormone?
Secreted by enteroendocrine cells
Hormone only acts within the vicinity that its released
Diffuses through extracellular space
E.g. somatostatin and histamine
hormones with both endocrine and paracrine mechanisms: glucagon-like peptide-1 (GLP-1), pancreatic polypeptide and peptide YY
What is neurocrine hormone?
Secreted by postganglionic non-cholinergic neurons of the enteric nervous system- acts like neurotransmitters
Hormone that affects nerves
E.g. vasoactive intestinal peptide (VIP), gastrin releasing peptide (GRP) and enkephalins
What are enteroendocrine cells?
Specialised epithelial cells located at the base of the intestinal crypts throughout the GI tract from stomach to colon
They have hormone containing granules concentrated at the basolateral membrane adjacent to capillaries that secrete their hormone in response to wide range of stimuli
Examples: K cell, I cell, L cell
