GI Physiology The Basics - Karius Flashcards
Enteric nervous system
Intrinsic nervous system Completely contained within the gut - esophagus to anus Myenteric plexus Submucosal plexus -motility -secretion -hormone release -blood flow
Submucosal plexus
In submucosa
Controls secretions, circulation and muscular is mucosae contraction
Myenteric Plexus
(aka Auerbach’s)
Between muscle layers
Controls motility
The 5 most common NTs of the enteric nervous system?
ACh - increases activity
VIP - increase secretion, decrease motility
Norepinephrine - decrease activity - especially motility
NO - major inhibitory NT of enteric NS
Opioids - primarily endorphins
What is the major inhibitory NT of enteric nervous system?
Nitric oxide - required to cause relaxation
2 diseases related to nitric oxide
Hirschsprungs disease - region tightly contracted, obstruction
Achalasia - LES doesn’t relax, swallowing painful
What enzyme is required for nitric oxide?
Nitric oxide synthase
What effect does sympathetics have on the GI system?
Decrease activity of intrinsic neurons
Depress most GI functions
-decrease blood, secretion, motility
-increase sphincter tone
What effect does parasympathetics have on the GI system?
Increase activity of intrinsic neurons
Excite most GI functions
-increase blood flow, secretion, motility
-relax sphincters
Local reflexes in the gut
Distension in stomach increases gastric motility
- neurons that mediate are located in enteric NS
- NO involvement of CNS or ANS
Long loop reflexes in the gut
- distension in the stomach
- relaxation in the colon
“get ready, here comes food”
Afferent to sympathetic ganglia, then back to gut
How do you name GI reflexes
First part of name - origin of the reflex
Second part of name - where the effect occurs
Explain the gastrocolic reflex
Origin - stomach (distension)
Effect occurs - colon (induces relaxation)
-long loop reflex
Longest reflexes in the gut
Cell body in dorsal root ganglion (not enteric) To CNS Back to gut Most are inhibitory Ex. response to pain (surgery)
Which type of reflex involves the CNS?
Longest reflex
-stimulus may arise from other viscera
Gastrin
Pyloric glands - G cells - peptide hormone elicited by dissension
Increase acid secretion, motility, pancreatic enzyme secretion
Travels via blood
Secretin
Peptide hormone
S cells of intestine
Presence of acid in duodenum
Travels via blood
What is secretin’s main job?
Protection against acid
- stomach - decrease gastrin, acid and motility
- pancrease and liver - increase bicarbonate
CCK-PZ
Cholecystokinin-pancreozymin I cells of intestine Peptide hormone Similar to gastrin Presence of fats in duodenum Travels via blood
Major role of CCK-PZ?
Pancreas - increase enzyme secretion (pancreozymin)
Gall bladder - contraction of gall bladder (cholecystokinin)
Also acts in brain, liver - satiety
Glucagon-like Peptide 1
(GLP-1) L cells of intestine Peptide hormone From proglucagon Stimulus: nutrients, esp fats and dietary fiber in intestine Travels via blood
Job of Glucagon-like Peptide 1
Increase - insulin secretion
Decrease gastric acid and motility
Glucagon-like Peptide 2
(GLP-2) L cells of intestine Peptide hormone From proglucagon Stimulus - nutrients - esp fats and dietary fiber, intestinal injury Travels via blood
Which hormone is a trophic factor for intestine?
Glucagon-like Peptide 2
Growth of villi
Mucosal hyperplasia
Motilin
Produced by stomach, small intestine, colon
Stimulus unknown - increases every 100 minutes between meals
Stimulates motility, especially the occurrence of the migrating motor complex
What is the oxygen state of the villus and why?
It is hypoxic all the time - leads to short life span
O2 from the artery diffuses across to the venous blood (down gradient)
GI blood flow
Venous blood - most to hepatic portal system, some back to heart
Sympathetic stimulation - vasoconstriction, may totally occlude
Parasympathetic - dilation
P-glycoprotein
MDR-1 gene product
P = permeability
MDR = multi-drug resistance
Cells expressing this protein survived drug doses that were toxic/lethal to other cells
Function - remove drugs/other shit from cell to lumen (prevent absorption)
What happens if there is less P-glycoprotein expression?
More drug in plasma
And vice versa
P-glycoprotein polymorphisms are suggested in susceptibility to
IBD and colon cancer
