Regulation of gut function Flashcards
What ganglia innervate the stomach, small intestine and colon?
coeliac ganglion - Stomach
superior mesenteric ganglion - Small intestine + ascending large intestine
inferior mesenteric and pelvic ganglion - Transverse colon to rectum
What is the neurotransmitter used in the sympathetic NS innervating the GI tract?
Norepinephrine-Only at effector organs
Where do the pre-ganglionic sympathetic neurones arise from in the spinal cord that innervate the stomach and colon?
Thoracic and lumbar spinal cord
Stomach (T6-9)
Colon (L2-5)
What does activation of the sympathetic NS do to the GI tract?
Inhibits its activities
What are the divisions of the GI tract NS?
How is the stomach, small intestine and proximal colon parasympathetically innervated?
Vagus nerve
What NT is used in the parasympathetic innervation of the stomach, small intestine and the proximal colon and where do the preganglionic neurones originate from?
ACh
Preganglionic neurons originate in dorsal vagal complex within brainstem from sacral spinal cord.
What does activation of the parasympathetic NS do to the GI tract?
Stimulates its activities
In the GI sympathetic NS, are the ganglia close or far from the effector organs?
Far
In the GI parasympathetic NS, are the ganglia close or far from the effector organs?
Close
What are the NTs in the GI NS?
ACh everywhere apart from sympathetic target organs
Where are neurones myelinated/unmyelinated in the GI NS?
Myelinated pre-ganglionically, Unmyelinated post-ganglionically
What is a plexus?
A network of interconnecting nerves
Where are the plexuses of the GI tract enteric(intrinsic) NS and which intestinal layers are they in?
Meissner’s plexus-Submucosa
Auerbach’s plexus-Muscularis Propria
What is the general function of the enteric NS?
“The 2nd brain”
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 is the function of Meissner’s(Submucosal) plexus?
Senses the local environment (gut lumen)
Controls secretion, blood flow, epithelial and endocrine cell function
What is the function of Auerbach’s(Myenteric) plexus?
Controls activity of muscularis propria
Controls gut motor (motility) function
tone, velocity of contraction and intensity of contraction.
Describe the pathway of the local enteric reflex
- Food enters gut and stretches smooth muscle
- Distension activates neurones in the myenteric plexus, chemicals in food stimulate submucosal plexus
- Sequential contraction/relaxation of circular+longitudinal muscles causes peristalsis
What are the actions of the circular and longitudinal muscles in peristalsis
Circular muscles contract behind the bolus
Longitudinal muscles contract in front of the bolus(Lumen widens)
What are the effects of the sympathetic nervous system on the enteric NS?
Reduces peristalsis
Reduces absorption
Reduces secretion
Reduces blood flow (via enteric nervous system and also directly)
What are the effects of the parasympathetic nervous system on the enteric NS?
Increases peristalsis
Increases absorption
Increases secretion
Increases blood flow
What is the cause and mechanism of Hirschsprung’s Disease?
Congenital absence of ganglion of myenteric and submucosal-No enteric NS
Tonal contraction without reciprocal relaxation
Intestinal distension proximal to a-ganglionic segment of bowel
Most will require surgery
What are enteroendocrine cells and what is their function?
Specialised epithelial cells located at the base of intestinal crypts throughout the GI tract, from stomach to colon
Possess hormone-containing granules concentrated at the basolateral membrane, adjacent to capillaries, that secrete their hormone in response to a wide range of stimuli
What molecules are secreted in the stomach?
gastrin, ghrelin, somatostatin and histamine
What moelcules are secreted in the pancreas?
insulin, glucagon, somatostatin and pancreatic polypeptide
What molecules are secreted in the duodenum?
secretin, CCK and somatostatin
What molecules are secreted in the colon?
PYY, GLP-1, Oxyntomodulin, neurotensin and somatostatin
What molecules are secreted in the small intestine?
PYY, GIP, GLP-1+2, Oxyntomodulin, neurotensin and somatostatin
What is the:
function,
place of production
requirements for secretion
of gastrin?
Stimulates gastric acid secretion by parietal cells in stomach
Synthesised in gastric antrum and upper small intestine
Release stimulated by:-
amino acids and peptides in the lumen of the stomach
gastric distension
vagus nerve
Release inhibited when pH of stomach falls below pH 3
What is the:
Place of secretion
function,
requirements for secretion
of secretin?
Secreted by the S cells of the upper duodenum and jejunum
Major stimulus is the presence of acid in the duodenum (pH falls below 4.5)
Function:
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
What is the:
function,
requirements for secretion,
place of secretion
for cholecystokinin?
Secreted by cells most densely located in the small intestine
Release stimulated by fat and peptides in the upper small intestine
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
Function of motilin?
Increases GI motility
What is the:
place of secretion,
function,
requirements for secretion
of GIP?
(glucose-dependent insulinotropic peptide)
Also known as Gastric inhibitory polypeptide
Secreted by mucosal K cells (predominant in the duodenum and jejunum)
GIP released following ingestion of a mixed meal
The only hormone with a response to all 3 macronutrient types (glucose, amino acid, fatty acids)
Likely stimulated by change in intraluminal osmolarity
Stimulates insulin secretion
What is the:
place of secretion
function
requirements for secretion
for GLP-1?
Produced in the small intestine and secreted from L cells
Release stimulated by the presence of hexose and fat
Induces satiety
Increases sensitivity of pancreatic beta-cells to glucose
What is the:
place of synthesis
requirements for secretion
function
for pancreatic polypeptide
Secreted by PP cells in the pancreas
Secretion stimulated by fat
Potential role in satiety
What is the:
place of synthesis,
function
requirements for secretion
of somatostatin
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
Inhibition of
gastric secretion
motility
intestinal and pancreatic secretions
release of gut hormones
intestinal nutrient and electrolyte transport
growth and proliferation
What is the:
place of secretion
function
of peptide YY?
Secreted from cells found throughout the mucosa of the terminal ileum, colon and rectum
Released from L cells post- prandially (particularly protein)
Reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion
What are the functions of the neuroendocrine hormones and where are they located?
(VIP, GRP, enkephalins)
Located within nerves in the gut
Vasoactive intestinal peptide (VIP) → relaxation of gut smooth muscle
Gastrin releasing peptide (GRP) → induces gastrin release
Enkephalins → increase smooth muscle tone
Where are neuroendocrine tumours found and give an example of one type and 2 ways to treat them?
Tumours of the neuroendocrine cells (which are found predominantly in the gastrointestinal tract and pancreas)
For example,
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 occurs in the gastric phase of gastric secretion?
Food causes distension in stomach, causing vagus nerve to innervate the brainstem, in turn stimulating more stomach secretion
-Stomach distension and food chemicals activate enteric(intrinsic) NS to stimulate secretions
What occurs in the cephalic phase of gastric secretion?
Smell, thought of food stimulates brainstem,
PS NS via vagus nerve innervates enteric plexus,
Post-ganglionic neurones stimulate secretion of gastrin, acid- and digestive enzymes
What occurs in the intestinal phase of gastric secretion?
Chyme in duodenum with pH<2 causes brainstem stimulation, inhibiting gastric secretions
Local acid/lipid reflexes also work on the enteric NS, reducing secretions
Secretin, GIP and cholecystokinin, released by the duodenum inhibit gastric secretions.
