Lecture 6 General Principles of GI Flashcards
what is the outermost layer of the gut wall
Serosa (protection)
what is just inside the serosa that shortens the bowel segment upon contraction
Longitudinal mucle
what is just inside the longtudinal smooth muscle that decreases the diameter of the lumen?
circular muscle
what muscle layer is deep to the circular muscle that causes changes in surface area of the epithelial surface?
Muscularis mucosa
mucosa with bundles of mucosal smooth muscles
what does polarized mean?
something is longer than it is wide
what nerve plexus in the gut call causes peristalsis?
Myenteric plexus
Where is the myenteric plexus located?
Between the longitudinal layer and the circularis muscles
What nerve plexus in the gut wall controls vasodilation and therefore secretion?
Meissner Plexus
TRUE or FALSE, GI smooth muscle has significantly interconnected with bundles of cells that contract in a single direction with big gap junction for easy ion flow?
TRUE
Do many or few connection exist between the major smooth muscle layers?
Few
Smooth muscle DOES NOT have action potential, what happens instead?
It is a slow wave rhythm of MEMBRANE POTENTIAL that goes off with stretch or other stimulus (only at the top an AP becomes possible with stimulus)
these action potentials that only occur at the top of waves are actually called?
spike potentials
(slow wave created by sodium leakage)
(spike potential created by Ca-Calmodulin)
Intrinsic innervation can happen w/o extrinsic sympathetic and parasympathetic influence, true or false?
True
In the extrinsic pathway, what autonomic system is inhibiting, and excitatory?
Parasympathetic is stimulating
Sympathetic is inhibiting
Through what route does parasympathetic stimulation excite the Gi tract?
Parasympathetic stim descends down Vagus CN X, and goes to both Myenteric and Meissner plexuses, which cause contraction and vasodilation/secretion
Besides parasympathetic stimulation increasing the membrane potential, what other two things influence it?
Local stretch, and acetylcholine
What besides the sympathetic stimulus causes inhibition of the GI tract?
Norepinephrine or epinephrine
Does the myenteric or submucosal/meissner plexus span the entire length of the GI tract?
Just the myenteric
the meissner only controls smaller portions of local mucosa
What protein is excreted with a protein meal touches the wall of the duodenum that increases secretions ahead of time?
Enterokinase
TRUE or FALSE, there are very few sensory fibers in the Myenteric plexus
TRUE
What 5 things can plexus cell bodies detect in the gut and promote excitation or inhibition as a result?
Stretch pH Irritation Hormones and signaling molecules Chemicals (like fats proteins carbs in duodenum)
She said just remember this….
Sensory cells ARE not epithelial cells
what is the visceral-visceral loop
a sensory system between the nerve fibers of the gut wall and the greater myenteric & submucosal/meissner plexus. This loop bypasses the need for higher regulation
The parasympathetic system innervates all GI structures as far as what?
Left colic flexure of colon
what nervous division supplies the descending colon, sigmoid, rectum, and facilitates defecation?
Pelvic splanchnic nerves from s2-s4
What symathetic plexus innervates liver, gall bladder, stomach, pancreas, large and small intestine to left colic flexure?
Celiac Plexus (with mostly NOREPI)
Gastrin is released in the G-cells (parietal) cells that stimulates the production of what?
HCL and promotes mucosal growth (producing Na/H exchangers)
Gastrin is located in what 3 places?
Stomach, duodenum, jejunum
Gastrin is stimulated by what three local factors?
Presence of proteins, stomach distention, and acetylcholine
Gastrin production is inhibited by what factor?
low pH (indirectly responsible for keeping esophogeal sphincter closed normally)
Cholecystokinin does what?
Stimulates bicarb and enzyme secretion from the pancreas, contracts the gallbladder, promotes pancreatic growth, inhibits gastric motility
Cholecsytokinin is located in what 3 structures?
I-cells of duodenum, jejunum, ileum
Cholecsytokinin is stimulated by what 3 things?
proteins, fats, and H+
Secretin does what?
promotes pepsin, promotes biliary and pancreatic bicarb secretion, and inhibits HCL secretion (anti gastrin hormone)
Secretin is found where?
S-cells of duodenum, jejunum, ileum
Secretin is stimulated by what 2 things?
Fat, and acids
What are the 2 phases of peristalsis induced by the myenteric plexus?
- Leading wave of distension
2. Peristaltic contraction
what occurs randomly in the gut, induced by stretch or presence of food bolus?
mixing movments (5-30 seconds in length)
