GI 3 Flashcards
what kind of neurons regulate GI function
ANS
Enteric nervous system
besides neurons, what else regulates GI function
Paracrine mediators (local cells from diffusion) Hormones (reach gut via blood)
what are the parasympa nuclei(and associated nerves) that supply to the Enteric nervous system
Vagal nucli( via Vagus Nerve) Sacral spinal cord (via pelvic nerve)
do both the sympathetic and parasympathetic supply to the enteric nervous system
Yes
what are the plexus’s assocaited with the enteric nervous system
Myenteric Plexus
Submucosal plexus
what part of the GI tract does the sympathetic have direct effect on asside from affecting it via the Enteric system
Blood vessels
what of the GI does the enteric system have an efect on
Smooth muscle
Secretory cells
Endocrine cells
Blood vessels
what level of the wall in the GI is the submucosal nerve plexus found
in the submucosa
what level of the wall in the GI is the myeneric nerve plexus found
Muscularis Exteerna
what do motor neurons of the ENS do
Muscle contraction
Gland function
what do Interneurons do in the ENS
regulate interactions between different layers of the GI tissues
what types of neurons are in the ENS
Sensory neurons
what types of receptors are found in the GI(used for reflexes
Mechanoreceptors
Osmoreceptors
Chemoreceptors
what initates reflex arcs of the GI tract
Distension of the wall
Chyme osmolarity
Chyme acidity
Chyme concentration
what does the long reflex of the GI involve
invovles the CNS (using afferent and efferent neurons from the GI walls)
- factors in sight, smell, taste
path of the long reflex of the GI
- stimulus in GI acts on receptors of GI walls
- afferent neurons to CNS from vagal sensory neurons
- efferent ANS (PNS or SNS)
- act on nerve plexus
- acts on smooth muscle or gland of GI wall
what does the the short reflex of the GI invovle
all that the long one does but lacks the afferent and efferent nerves from the CNS (CNS not invovled)
what types of hormones can act on the GI
peptides
neurotransmitter/neuroendocrine hormones
what are the 4 hormones that regulate digestion
Gastrin
Cholecystokinin (CCK)
secretin
Glucose-dependent Insulinotropic peptide
what is the CCK feedback look
CCK stimulated by fatty acid
CCK stimulates enzyme production of pancrease
enzyme production reduces CCK activation
Do hormones of GI act on only 1 type of cell
No, work on multiple
what cells can CCK activate
stimulate Pancreas, liver, gallbladder,
inhibit stomach emptying
do each hormone of GI act along
can be synergistic (one can poentiate the other)
what are the phases of GI control
Cephalic Phase
Gastric Phase
Intestinal
what nerve fibers stimulate the Cephalic phase
Parasympa nerve fibers affecting the ENS
what initiates the cephalic phase
When recetpors in head are stimulated
what is involved in control of the gastric phase
short and long neural reflexes
Gastrin
what all causes the gastric phase
Distension
Acidity
Amino acids
Peptides
what is involved in control of the intestinal phase of Gi control
Short and long neural reflexes
Secretin
CCK
GIP
what causes the Intestinal phase
Distesion
Acidity
Osmolarity
Various digestive products
what is the immune function of stomach
Kills many bacteria
what does the stomach do to food
Initiates digestion of food
what does the stomach deliver to the dueodenum
Chyme
what determines the rate that the stomach delivers chyme to the duodenum
secretion rate of bile salt, bicarb, digestion enzymes
rate of enzyme breakdown of carbs, fats, and proteins
small intestine transit
what are the 3 anatomic sections of the stomach
Fundus
body
Antum
what are the glandular regions of the stomach
Oxytic (mesial)
Pyloric (distal)
what are the cells of the gastric pit
mucous neck cells
Cheif cells
Parietal cells
what do parietal cells produce
HCL
Intrinsic factor
where is HCL produced
By parietal cells in the fundus and body (oxyntic gland area)
where is intrinsic factor produced
By parietal cells in the fundus and body (oxyntic gland area)
what do chief cells produce
Pepsinogen
where is pepsinogen produced
by chief cells in the body and the antrum (oxyntic and pyloric gland area)
where is mucous produced
in mucous neck cells throughout the stomach
where is bicarb produced
Epithelial cells through the stomach
where is gastrin produced
G cells in the NAtrum (pyloric gland area)
where is somatostatin producd
D cells through the stomach ath the base of gastric gland
where is histamine produced in the GI tract
Enterochromaffin-like cells
how is HCL secereted
- Cl brough in from the Capillary by being transported aginst Bicarb(makes spare H+ from carbonic anhydrase)
- Cl flows into staomach along with K
- ATP helps pump H into stomach and pump K back into the cell
what is invovled in regulating acid secretion
Tubulovesicular membrane
Intracellular cancliculus
what is the strongest HCL stimulant
Histamine
what triggers histamine release
Gastrin or ACh
do Gastrin and Ach only act on histmaine to relaese HCL
No, can directly act on Parietal cells
what is the intracellular message for relase of HCL from pareital cells
Second messenger activitation
what is the action of Somatostatin
Inhibit HCL
what does Somatostatin act on to inhibit HCl secretion
G cells
Pareital cells
what are the cephalic aspects that regulat HCl secreteion
Sight
Smell
taste
Also mech stimulation from chew and swallowing
what does the cephalic regulation of HCl seceretion active
PNS to produce Ach
what is the intesinal phase effect on HCl secretion
initially enhances HCl secretion by later inhibits it
what does the pH of chyme need to be for secretin to be produced
less than 3
what aspects inside the stomach decrease HCL production via CCK
High H+
amino acids
Fatty acids
- all stimulate CCK
what increases gastrin secretion
gastric phase distesnion, protein, peptides, amino acids
activity of gastrin
act on parietal cells to increase HCL secretion
why does HCL degrade gatric tisssue
Muscus neck cells
Gastric epithelial cells produce Na, Cl, K , HCO3 that keeps the surface of cells at ph 7
how is pepsin produced
released as pepsinogen as a zymogen (proenzyme to be cleaved)
- cleaved by HCL into Pepsin
why doesn’t pepsin degrade stomach tissue
do to mucous layer so, it is not activated till its in the Low pH zone of the stomach
how does gatric motility occur neuologically
does like peristallic waves with action potentials occuring once cresting AP
what does gastric motility/emptying factors relate with
same factors that affect HCl secretion
what inhibits the secretion and motility in the stomach
Secretin and CCK (enterogastrones)
what stimualtes the secretion of Secretin and CCK
increased acidty, fats, amino acids, hypertonicit, distenstion in the dueodenum
what are the exocrine products of the pancrase
Bircab Digestive enzymes (lots
how does the pancreas activate inactive enzyme
- Pancrease releases Typrinogen
- trypsinogen converted to trypsin by membrane bound enterokinase
- Trypsin takes inactive enzymes to active enzymes in the intestinal lumen
what potentiates CCK secretion
Secretin
how is bicarb secreted
Like HCl but in reverse
how is bicarbonate secretion regulated
Hormone: secretin
Feedback: acidity
what does the liver do for digestion
Produces bile
where does the liver secrete bile
Canaliculi (small ducts)
what do canaliculi drain into
convege and drain into larger bile ducts
what is found in bile
Bile salts (and other salts) Lecithin Cholesterol(related to bile salts) Bile pigments (bilirubin) and other metabolic end products trace metal Bicarb
what stimulates secretion of bicarb
stimulation of epithelial cells of ducts by secretin
how much bile salt does the liver synth
20-60mg of bile salts
how much bile salt does is secreted a day
1,200-3,600 mg
how can more bile salts be secreted than synthesized
recycled through the enterohepatic circulation
increase in plasma cck lead to what
increase in bile flow into duedenum
when is absorption maximized
when chyme/bolus is continuously brough into contact with the intestinal tissue
- also importat to contract small intestine
what are the types of smooth muscle contraction
Peristalsis
Segmentation
what is peristalsis
Progressive contraction of successive sections of circular smooth muscle
what is segmentation
Closely spaced contractions of circular muscle layer
what happens when segmentation is rhythmic
chyme/bolus is mixed and slowly moved downward
how does the food move during absorption in the small intestine
segmental contraction
what contractions occur after must absorption has occured
peristaltic contraction
what drives peristalsis
migrating myoelectric complex
where does the myoelectric complex that drives peristalsis begin
lower stomach
speed of the myoelectric complex that drives peristalsis
travels 2 feet prior to dying
what initiates the myoelectric complex of peristalsis
intestinal hormone motilin
how does the food bolus enter the large intestine
Ileocecal valve (sphincter
what makes up the bolus that enters the large intestin
small intestine secretion
undiestable foods
what is the cause of farts
bacteria fermenting stuff in the large intestine
what is the primary purpose of the large intestine
tranpsort Na from lumen to blood
what is bicarb secretion in the large intestine coupled with
Cl ion absorption
what is the benifit of bacterial fermentation of food bolus
absorb nutrients from food
what does the large intestine do with the remaining food folus
Eliminate it from the body
how does motility of the large intestine control
occurs as slow segmentation contracts
how often do peristaltic-like contractions in the large intestine occur
3-4 times per day
what is the roll of the mouth in digesting
Chewing
Salivation
Amylase
Lipase
what is the roll of the stomach in digestion
HCl
Pepsinogen
Lipase
Gastrin
what is the roll of the small intestine in digestion
Hormones (secretin, Cholecystokinin)
what is the roll of the pancreas in digestion
proteases
Lipase
Amylase
HCO3
what is the roll of the liver in digestion
Bile
what is the roll of the small intestine in digestion
absoprtion (carbs proetin, fats, vitamines, minerals)
what is the roll of the large intestine in digestion
Absorption (Na, Cl, water)
what determines the rate at which food moves through the stomach
Pacemaker cells
magnitude determined by excitatory stimuli
what kind of contractions are found in the stomach
Peristalsis from body to pyloric sphincter
what kind of contractions occure in the smalle intestine
Segmentation and peristaltic contraction
what controls peristalsis in the small intestine
Migrating myoelectric complex (initiated by motilin)
how does the large intestine move
Slow segmentation contractions in massive movements
