Regulation of Gut function Flashcards
What is the gut nervous system divided into?
- AUTONOMIC(extrinsic) and ENTERIC(intrinsic)
- Autonomic is split further into the Parasympathetic and Sympathetic
Where do the sympathetic preganglionic neurons that supply the GI tract come from?
-Comes from the THORACIC and LUMBAR region of the spinal cord
T6-9 =stomach
L2-5 =colon
What do the sympathetic Post-Ganglionic neurons innervate?
COELIC GANGLION-stomach
SUPERIOR MESENTERIC GANGLION- small intestine
INFERIOR MENSENTERIC GANGLION +PELVIC GANGLION- colon
What is the main neurotransmiiter of the sympathetic neves of the gut?
Norepinephrine(noradrenaline)
What effect does the activation of the Parasympathetic and Sympathetic nervous system have on the GI Tract?
Sympathetic- INHIBITS activities:
- reduces peristalsis
- reduces absorption and secretion
- reduces blood flow directly and via enteric nervous system
Parasympathetic- STIMULATES GI Tract:
- increases peristalsis
- increases absorption and secretion
- increases blood flow
What is parasympathetic innvervation to the stomach, mall intestine and proximal colon supplied by?
VAGUS NERVE
Where do the pre-ganglionic neurons of the GI tract originte from?
DORSAL VAGAL COMPLEX within the BRAINSTEM form the SACRAL SPINAL CORD
-these then synapse with the postganglionic neurones very nerar the organ they supply
What neurotransmiiter is released in parasympathetic innervation?
Acetylcholine
What are key features of the Enteric (intrinsic) nervous system?
-2nd brain as even if it is cut of from spinal cord it can work AUTONOMOUSLY
-Can interact with the parasympathetic and sympathetic nervous system
What are the parts of the enteric nervous system and where are they located?
MEISSNERS(submucosal) PLEXUS-in the submucosa of the GI tract(stomach, colon, intestine etc)
AUERBACHS (myenteric) PLEXUS- in Muscularis propia (muscle layer) inbetween the circular and longitudinal muscle
What is the function of the submucosal plexus?
- senses the local environment(gut lumen)m e.g chang in pH, chemicals, proteins etc
- stimulates secretion of hormones, enzymes and mucus to aid digestion(epithelial and endocrine function)
- bllod flow
Wha tis the function of the Myenteric plexus?
- controls motility and activity of the muscle layer of the gut
- senses things and responds by changing intesity and velocity of contraction
- controls activity of MUSCULARIS EXTERNA
Describe the local reflex of the enteric system?
1) Food enters gut lumen and stretches the intestinal smooth muscles
2) Distention of the gut causes stimulation of the snesory neurons in the myenteric plexus
3) Chemicals in food stimulate sensory neurons in the submucosal plexus
4) This results in muscles contraction/relaxtion=PERISTALSIS and the release of enzymes to aid digestion
What is peristalsis?
- wave of muscular contractions that moves the Bolus of food along the GI tract
- CIRCULAR muscles behind the bolus contract while LONGITUDINAL muscles in front of the Bolus relax and vice versa
Describe the interaction between your sympathetic, parasympathetic(extrinsic) and enteric(intrinsic) nervous system
Intrinsic/enteric -food stimulates local response via myenteric and submucosal plexus which cause peristalsis and secretions
Interaction-food can cause pain, fullness etc which feedbacks to CNS which then interacts with enteric nervous system via sympathetic and parasympathetic nervous system
What is Hirshsprungs disease?
- born with ABSENCE of GANGLIONS in MYENTERIC and SUBMUCOSAL PLEXUS
- Causes tonal contraction of rectum without relaxation afterwards= diahorrhea
- Above the rectum the intestine distends/becomes enlarged
- most will require urgery to help it
What are the 3 types of gut hormones and where are they secreted from?
ENDOCRINE:
- hormone released intot he bloodstream
- enteroendocrine cells
PARACRINE:
- acts only in the area it is released
- enteroendocrine cells
NEUROCRINE:
- hormone that effects nerves
- secreted from post-ganglionic post cholinergic neurons of the enteric system
Gives examples fro each hormone type?
ENDOCRINE-Gastrin, CCK, glucose dependent insulinotrophic peptide(GIP), Motilin
PARACRINE-somatostatin, histamine
NEUROCINE-vasoactive intestinal peptide(VIP), Gastrin release peptide(GRP), enkephalins
Descriebt he enterendocrine cells?
- located at base of intestinal crypts
- Have granuales that contain hormones at the basolateral membrane next to the capillaries
- stimuli(small peptides, amino acids, fatty acids, oral glucose, distention of organ, vagul stimulation) causes the hoemones in these granuales to be released into theblood stream
Where are different gut hormones released in the GI tract
Stomach- Gastrin, Ghrelin, Histamine, somatostatin
Duodneum- CCK, secretin, somatostatin
Pancreas-insulin, Glucagon, Somatostanin
Second part of the small bowl up to the ileum- PYY, GIP, GLP-1, GLP-2, Oxyntomodulin, Neurotensin, Somatostatin
Colon-PYY, GLP-1, Oxytomodulin, Neurotensin, Somatostatin
Where is Gastin synthesised and secreted?
Gastic ANTRUM(stomach) and the small intestine
What stimulates the release of Gastrin?
- amino acids and peptides in the lumen of the stomach
- Gastric distention
- Vagus nerve
What is the function of Gastrin?
stimulates Gastric Acid secretion from the parietal cells in the stomach
When is the release of Gastrin inhibited?
when pH in the stomah falls below pH 3
Where is Secretin secreted?
by the S-CELLS in the UPPER DUODENUM and JEJUNUM
What stimulates the secretion of secretin?
presence of acid in the duodenum which causes the pH to fall below 4.5
What is the function of secretin?
- stimulates pancreatic BIOCARBONATE (more secreted in the presence of CCK) to neutralise stomach acid
- inhibit gastric acid and gastric emptying
- Inhibt gastrin, acid secretion, and growth of stomach mucosa
- stimulates bilary secretion of bicarbonate and fluid
- trophic effect on the exocrine pancreas
Whhere is CKK secreted?
-by cells most densly located in the small intestine
Wha tis the secretion of CKK stimulated by?
-fats and peptides in the upper bowel
What is the function of CKK?
- Stimulates pancreatic enzyme release(lipase, amylase, protease)
- delays gastric emptying
- stimulates gallbladder contraction and relaxtion of the sphincter of ODDI
- decrease food intake and meal size(As it senses that there is food already present in the small bowel)
- trophic effects on the exocrine pancreas and bladder
What is another name for Glucose dependent insulinotrophic peptide(GIP)?
Gastric inhibitory polypeptide
Where and when is GIP secreted?
-secreted by mucosal K-CELLS which are predominent in the DUODENUM and JEJUNUM
-secreted after a meal
What is the function of GIP ?
The only hormone with a response to all 3 macronutrient types-glucose, amino acids, fatty acids
-stimulates the release of insulin from the pancreas
What stimulates the secretion of GIP?
-likely the change in intraluminal osmolarity
What is the function of Motilin?
-Increase Gastrointestinal motility
Where is somatostatin synthesises and secreted?
Synthesised in endocrinal D-CELLS of the GASTRIC and DUODENAL MUCOSA and the PANCREAS
What is the function of somaostatin?
UNIVERSA L INHIBITOR: inhibits
- Gastric secretion
- motility
- intestinal and pancreatic secretions
- release of gut hormones
- intestinal nutrient and electrolyte transport
- growth and proliferation
What stimulates the secretion of somatostatin?
In response to a mxed meal
Where is GLP-1 made and secreted?
-small bowel secretd from L-CELLS
What stimulates the release of GLP-1 ?
presence of HEXOSE and FAT
What is the fucntion of GLP-1?
- INDUCES SATIETY
- increases sensitivity of pancreatic beta cells to glucose
Where is pancreatic polypeptide hormone secred?
what stimulates its secretion?
What is its function?
- secreted by PP CELLS in the pancreas
- stimulated by FAT
- potential role in satiety
Where is Peptide YY hormone secreted?
What is its function?
- secreted from L- cells found throughout the mucosa of the terminal ileum, colon and rectum
- reduces intestinal motility, gallbladder contraction and pancreatic exocrine secretion
Wha tare the 3 different neurocrines and there function?
located in nerves of the gut
VIP-relaxation of the smooth gut muscle
GRP-induces gastrin release
Enkephalins-increase smooth muscle tone
What are neuroendocrine tumours?
Give an example and its treatment?
tumour caused by the proliferation of neuroendocrine cells (prodominently in GI Tract and pancreas)
ZOLLINGER ELLISON SYNDROME-tumour of GASTRIC CELLS causing overproduction of GASTRIN and ACID resulting in stomach and INTESTINAL ULCERATION
Treat with protein pump inhibitor to inhibit acid secretion
-treat with somatostatin analogues to halt growth and reduce secretion
What are the phases of Gastric secretion?
1) Cephalic
2) Gastric
3) intestinal
What happens in the cephalic phase of gastric excretion?
1) smell, thought, sight of food and taste stimulate brain steM
2) PARASYMPATHETIC nervous system via the VAGUS NERVE stimulates the enteric plexus
3) post ganglionic neurons stimulate the decretionof gastrin, acid(parietal cells, and enzmes(chief cells)
4) Gastrin released into blood stream and induces secretion from parietal and chief cells
Describe what happens in the Gastric phase?
1) lasts 3-4 hours. Food arrives in the stomach and causes distension whcih causes signals via the VAGUS nerve to the brain stem
2) this stimulates stomach secretion
3) distention of the stomach and chemicals of the food also activate the ENTERIC nervous system to increase stomach secretion
Describe the intestinal phase of Gastric secretion?
1) food is now partially digested. chymw in the duodenum with pH <2 or lipidds stimulate stretch and chemoreceptors generate action potentials to the brain stem to inhibit PARSYMPATHETIC nervous system therefore inhibiting gastrin secretion
2) local reflexes activates by acids and lipids also act on the enteric nervous system to inhibit gastric secretions
3) secretin, gastrin inhibitory polpeptide and cholecystikinin(CKK) released by the duodenum inhibit gastric secretions
