Physio- General GI Flashcards
Name the 5 layers of the GI tract wall, starting from the outside
serosa –> longitudinal smooth muscle –> circular smooth muscle –> submucosa –> mucosa with mucosal muscle
The fibers of the longitudinal muscles are arranged in _______ to work together as a syncytium.
bundles
How does the bundles work together to contract as a unit?
Gap junctions
What causes the membrane potential to rise in slow waves?
intersitial cells of Cajal
True or False: slow waves are partial action potentials.
FALSE. they never reach the threshold potential without an external influence.
How do the interstitial cells of Cajal cause a slow change of muscle membrane potential?
They allow ions into the cell periodically to generate a slow wave between muscle fiber cells
These are the action potentials of the gut muscle, when the membrane potential becomes more positive than the threshold potential (-40mV)
Spike potential
What types of channels does the GI smooth muscle use to cause the spike potentials?
Ca-Na channels
different than neurons
Does stretching the muscle, Ach, and some GI hormones increase or decrease GI activity?
increase!
Case: you prescribe an anti-acetylcholinesterase to a patient for the treatment of myasthenia gravis. What is a common complaint for using such drug?
Diarrhea. The excess Ach activation causes POOOOOOOOOOOOOOOOOOOOP
Does NE and E increase or decrease GI activity?
decrease
What is the main function of the myenteric plexus?
controls the GI MOVEMENTS
remember “my-“ means “muscle”
So where in the gut wall does the myenteric plexus lie?
In the longitudinal and circular muscle layers
What happens to the musculature when the myenteric plexus fires?
It increases tonic contraction/tone of the gut wall –> increasing intesity and rhythm of contractions
What is the purpose of the use of VIP from the myenteric plexus?
It inhibits some sphinter muscles along the GI tract to keep the poop flowing.
What is the general role of the submucosal plexus?
controls the fxn of the inner wall
What happens if a signal from the GI epithelium stimulates the submucosal plexus?
It locally regulates intestinal secretion, absorbtion and contraction of the submucosal muscle.
What are the 2 sources of parasympathetic innervations to the gut?
Vagus nerve (X) and sacral parasympathetics (S2-4)
Where are the postganglionic neurons for the PANS innervation to the gut?
In the wall! they’re part of the submucosal and myenteric plexuses.
Gastrin- stimulus for secretion
Proteins
Gastrin- inhibiton for secretion
stomach acid
Gastrin- site of secretion
G cells of the stomach antrum, D&J
Gastrin- actions
stimulates acid secretion
CCK- stimulus
Fat
CCK- site
I cells of DJI
CCK- action
Gallbladder contraction, pancreatic enzyme secretion
Secretin- stimulus
Acid
Secretin- site
S cells of DJI
Secretin- action
Pancreating and biliary HCO3 secretion
GIP- stimuli
Protein, fats
GIP- site
K cells of D&J
GIP- action
inhibits gastric acid secretion
Motilin- stimuli
fasting
Motilin- site
M cells of D&J
Motilin- action
increases gastric and intestinal motility
What is the most basic propulsive movement of the gut?
Peristalsis
What triggers peristalsis?
distention of the gut
What are the types of cells on the liver sinusoids that remove bacteria that might enter the GI tract?
Reticuloendothelial cells
When is blood flow the the villi increased?
Genereally, when there is increased gut activity (like right after u eat)
Which 4 intestinal hormones cause vasodilation and increased blood flow to the villi?
CCK, VIP, gastrin, and secretin
Which 2 factors are released by GI glands that cause vasodilation?
Kallidin and bradykinin
