Lecture 10 Intro GI Flashcards
what kind of cells is the serosa?
outer layer of CT, simple squamous epithelium
Layers of the Gut Tract Wall (Outer to Inner)
- Serosa
- Longitudinal smooth muscle
- Myenteric (Auerbach)
4) Circular smooth muscle
5) Meissner’s plexus
6) Mucosa
where is the serosa missing?
esophagus
what forms the enteric nervous system?
Myenteric (Auerbach) and Meissner’s plexus
how are the neurons supported in the enteric nervous system?
by intrinsic glial cells
Is the myenteric plexus excitatory or inhibitory?
What hormones does it use?
excitatory
Ach and NO
what kind of neurons does the myenteric plexus consist of?
what does it control?
linear chain of interconnecting neurons
controls intestinal smooth muscle, participates in tonic and rhythmic contractions
What are the effects of the myenteric plexus?
Increases VITR
velocity (of excitatory waves), intensity, tonicity, rate
What does meissner’s plexus control?
GI secretion, absorption, local blood flow
also helps control local contraction of submucosal muscle
aka submucosal plexus
What are the layers of the gut tract wall?
submucosa - thicker than lamina propria, has blood vessels
mucosa - single cell layer, continuous sheet lining G.I. tract
what does the mucosa include?
lamina propria - loose CT with nerves, blood vessels, glands
muscularis mucosa - thin layer of smooth m., makes folds
what is characteristic of propulsive movements?
contractile ring
stimulus is distension, STRONG parasymp. signals, irritation
requires Myenteric (Auerbach) plexus
travels any direction
what are the characteristics of mixing movements?
may be caused by peristaltic contractions
local, intermittent contractions in gut wall
slow waves are not ____ ______.
what is the average intensity and frequency?
action potentials
I: 5-15mv Freq: 3-12 (increases from stomach to duodenum)
What kind of cells are the smooth muscle cell electrical pacemakers and what do they generate?
Cells of Cajal generate slow waves
slow wave –> spike potential –> muscle contraction
what are spike potentials? what is their threshold potential? how long do they last?
true action potentials
-40mv
10-20ms or 10-40x as long as normal AP
what kind of channels do spike potentials open?
Calcium
True or False
Calcium channels open rapidly and close slowly
FALSE
open slowly
close rapidly
What factors cause depolarization?
stretching of muscle
Ach (PS)
GI hormones
what causes hyperpolarization
NE and Epi
Sympathetic nerve stim
what causes tonic contractions
repetitive spike potentials
hormones
continuous entry of calcium ions
What g.i. reflexes result from the gut to prevertebral symp. ganglia and then back to g.i.?
gastrocolic - colon evacuation
enterogastric - inhibit stomach motility and secretion
colonoileal - empty ileum to colon
What g.i. reflexes result from gut to spinal cord/brain stem and back?
pain reflex - inhibits entire g.i. tract
defecation - from colon/rectum to spinal cord and back
stomach/duodenum reflex - to brain stem and back control gastric motor and secretory activity
Gastrin stimulus and site
protein, distension, nerve action
G cells of antrum, D, J
CCK stimulus and site
protein, fat, acid
I cells of DJI
Secretin stimulus and site
fat, acid
S cells of DJI
GIP stimulus and site
protein, fat, carbs
K cells of DJ
Motilin stimulus and site
fat, acid, nerve action…we are all FANs of motilin
M cells of DJ
Gastrin action
stimulates gastrin secretion and mucosal growth
CCK action
stimulates pancreatic enzyme secretion stimulates pancreatic bicarb secretion stimulates growth of exocrine pancreas inhibits appetite inhibits gastric emptying
Secretin action
stimulates pepsin secretion stimulates pancreatic bicarb secretion stimulates biliary bicarb secretion stimulates growth of exocrine pancreas inhibits gastric acid secretion
GIP action
stimulates insulin release
inhibits gastric acid secretion
Motilin actions
stimulates gastric and intestinal motility
secreted during fasting
what are the motor functions of the stomach
storage of food
mixing of food with gastric secretions
slow emptying of chyme into the small intestine
what 3 routes mediate the enterogastric nervous reflexes?
- directly from duodenum to stomach through enteric nervous system in gut wall
- extrinsic nerves going to prevertebral ganglia, then back inhibitory symp nerve fibers to stomach
- vagus nerves to brainstem
what factors are continually monitored in the duodenum that can initiate these reflexes?
- degree of distension in duodenum
- irritation of duodenal mucosa
- acidity of duodenal chyme
- breakdown products (protein) in chyme
what hormones control feedback from duodenum?
CCK - most potent
GIP and secretin a little
what are the 2 types of movements in the small intestine?
mixing and propulsive contractions
what controls intestinal movement?
- gastroenteric reflex initiated by distension via myenteric
- gastrin, CCK, insulin, motilin, serotonin
- irritation of intestinal mucosa
- gastroileal reflexes
what are the principal functions of the colon
water and electrolyte absorption from chyme
fecal storage
what are produced by large circulare constrictions plus contractions of the teniae coli?
haustrations
