Regulation of gut function Flashcards
What sympathetic ganglion supplies the stomach?
Ceoliac ganglion
T6-9
What sympathetic ganglion supplies the small intestine?
Superior mesenteric ganglion
What sympathetic ganglion supplies the colon?
Inferior mesenteric and pelvic ganglion
L2-5
What Neurotransmitter is used for the sympathetic nervous system supplying the gut?
Norepinephrine / Noradrenaline
What does the activation of the sympathetic nervous system inhibit?
Activities of the gastrointestinal tract
What nerve supplies the parasympathetic innervation to the stomach, small intestine and proximal colon?
Vagus nerve
Preganglionic neurones orginate in x within the brainstem from sacral spinal cord?
x - dorsal vagal complex
What neurotransmitter is used for parasympathetic innervation to gut?
Acetylcholine
Activation of parasympathetic nervous system x the gastrointestinal tract.
x- stimulates
What are the characteristics of the enteric nervous system?
- Autonomous
- Can also interact with sympathetic and parasympathetic nervous system
- The wall of the gastrointestinal tract contains many neurons – 2nd only to the brain
What are the myenteric and submucosal plexus?
Plexus : network of intersecting nerves
Myenteric is the outer plexus, lies between the circular muscle and longitudinal muscle
Submucosal is the inner plexus and lies between the mucosa and muscles
Found in the walls of the gut
What is the function of the myentreric plexus?
Myenteric (Auerbach’s) plexus :
controls activity of
- muscularis propria
- controls gut motor (motility) function
- tone, velocity of contraction and intensity of contraction.
What is the function of submucosal plexus?
senses the local environment (gut lumen)
controls secretion, blood flow, epithelial and endocrine cell function
How does the enteric system control the peristaltic local reflex?
Food enters and stretches smooth muscles –>
stimulates sensory neurones in myentric plexus = peristaltic wave ( Sequential contraction/relaxation of circular and longitudinal muscle by inhibitory/excitatory neurotransmitter cause peristalsis, which allows food to move along the GI tract )
- chemicals in food stimulate sensory nuerones –>
submucosal plexus, increase blood flow and secretion
What does the sympathethic nervous system do to digestion? - ( 4 )
reduces peristalsis
reduces absorption
reduces secretion
reduces blood flow (via enteric nervous system and also directly)
What does the parasympathethic nervous system do to digestion? - ( 4 )
increases peristalsis
increases absorption
increases secretion
increases blood flow
- although the gut can work without the para/sympathetic system these can enhance digestion
What are the characteristics of Hirschsprung’s disease?
Most common cause of neonatal bowel obstruction
- Congenital absence of ganglion of myenteric and submucosal ( enlarged colon )
Effect:
Tonal contraction without reciprocal relaxation
Intestinal distension proximal to aganglionic segment of bowel
Treatment :
Most will require surgery
What Endocrine hormones are involved in gut regulation?
gastrin, cholecystokinin, secretin, glucose-dependent insulinotropic peptide (GIP), motilin
What Paracrine hormones are involved in gut regulation?
somatostatin and histamine
hormones with both endocrine and paracrine mechanisms: glucagon-like peptide-1 (GLP-1), pancreatic polypeptide, and peptide YY
What Neurocrine hormones are involved in gut regulation?
secreted by postganglionic non-cholinergic neurons of the enteric nervous system
hormone that affects ‘nerves’
vasoactive intestinal peptide (VIP), gastrin release peptide (GRP), and enkephalins
Where are enteroendocrine cells found? ( release hormones )
specialised epithelial cells located at the base of intestinal crypts throughout the GI tract, from stomach to colon
What stimuli cause enteroendocrine cells to release their hormones from their granules?
these stimuli include small peptides, amino acids, fatty acids, oral glucose, distension of an organ, and vagal stimulation
What stimulates Gastrin release?
amino acids and peptides in the lumen of the stomach
gastric distension
vagus nerve
What hormones are secreted by duodenum?
Secretin
CCK
Somatostatin
What hormones are secreted by Pancreas?
Insulin
Glucagon
Somatostatin
Pancreatic polypeptide
What hormones are secreted by stomach?
Gastrin
Ghrelin
Somatostatin
Histamine
What hormones are secreted by the small bowel?
Peptide YY
Gastric inhibtory peptide
GLP-1
GLP-2
Oxyntomodulin
Neurotensin
Somatostatin
What hormones are secreted by colon?
PYY
GLP-1
Oxyntomodulin
Neurotensin
Somatostatin
What affect does Gastrin have on digestion?
Stimulates gastric acid by parietal cells
Trophic effect on mucosa of small intestine, colon and stomach - causing them to growth
gastrin release is stopped when pH falls below 3
Where is Secretin secreted from?
When?
Secreted by the S cells of the upper duodenum and jejunum
Major stimulus is the presence of acid in the duodenum (pH falls below
Functions of Secretin?
- stimulates pancreatic bicarbonate secretion (effect potentiated by CCK)
- inhibition of gastric acid and gastric emptying
- inhibits gastrin, acid secretion, and growth of stomach mucosa
- stimulates biliary secretion of bicarbonate and fluid
trophic effect on the exocrine pancreas
Where is Cholecystokinin secreted from and when?
Secreted by cells most densely located in the small intestine
Release stimulated by fat and peptides in the upper small intestine
What are the functions of CCK?
- stimulates pancreatic enzyme release (lipase, amylase, proteases)
- stimulates gallbladder contraction and relaxation of the sphincter of Oddi
- delays gastric emptying
- decreases food intake and meal size
trophic effects on the exocrine pancreas and gallbladder
Where does Glucose-dependent insulinotropic peptide (GIP) get secreted from?
Secreted by mucosal K cells (predominant in the duodenum and jejunum)
GIP released following ingestion of a mixed meal
Likely stimulated by change in intraluminal osmolarity
What is special about GIP?
The only hormone with a response to all 3 macronutrient types (glucose, amino acid, fatty acids)
What does GIP do?
Stimulates insulin secretion
What does Motilin do?
Increases gastrointestinal motility
Where is Somatostatin synthesised and released?
Synthesized in endocrine D cells of the gastric and duodenal mucosa, pancreas
Somatostatin is a universal inhibitor (Endocrine Cyanide)
Release in response to a mixed meal
What does somatostatin inhibit?
Inhibition of gastric secretion motility intestinal and pancreatic secretions release of gut hormones intestinal nutrient and electrolyte transport growth and proliferation
Where is GLP 1 produed?
Produced in the small intestine and secreted from L cells
Release stimulated by the presence ofhexose and fat
What are the functions of GLP 1?
Induces satiety
Increases sensitivity of pancreatic beta-cells to glucose
where is pancreatic polypeptide released and when?
Secreted by PP cells in the pancreas
Secretion stimulated by fat
Potential role in satiety
Where is Peptide YY secreted from and when?
Secreted from cells found throughout the mucosa of the terminal ileum, colon and rectum
Released from L cells post- prandially (particularly protein)
What does PYY do?
Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion
Where are neurocine hormones located?
Located within nerves in the gut
VIP, GRP, Enkephalins
What does VIP do?
Vasoactive intestinal peptide (VIP) → relaxation of gut smooth muscle
What does GRP do?
Gastrin releasing peptide (GRP) → induces gastrin release
What do Enkephalins do?
Enkephalins → increase smooth muscle tone 0 inhibit peristalisis, work on opoiod receptors
What are Neuroendocrine tumours?
Tumours of the neuroendocrine cells (which are found predominantly in the gastrointestinal tract and pancreas)
What are the characteristics of Zollinger Ellison Syndrome?
tumour of gastric cells causing overproduction of gastrin and acid resulting in stomach and intestinal ulceration
- treatment with proton pump inhibitor to inhibit acid secretion - role for somatostatin analogues to halt tumour growth and reduce secretion
What controls the Cephalic phase?
Vagus
What controls the Gastric phase
Local nervous system - secretion
Vagal reflexes
gastrin-histamine stimulation
What controls the Intestinal phase?
Nervous mechanisms
Hormonal mechanisms
