GI Motility Flashcards
What is the major site of DIGESTIVE & ABSORPTIVE processes?
Small Intestine
Describe the muscle types involved in the digestive tract as you move down the esophagus
Starts as skeletal, third of the way down is mixed with smooth, then after halfway is all SMOOTH
Job of Epithelium and mucosa surrounding the lumen?
Secretions & Absorption
Job of the circular and longitudinal muscles of the gut?
motility
What Accessory organs provide secretions into the digestive tract?
Pancreas & Liver
Facing the lumen are elaborate folds of ________ all lined with __________ cells.
VILLI, EPITHELIAL
What is the name of the 1st layer of muslce which is associated with the shape/SA of mucosa itself?
Muscularis Mucosa
What is the name of the 2nd layer of muscle which contains the circular and longitudinal muscles?
Muscularis Externa
What Nervous system is exclusive to the gut?
Enteric
The Enteric NS has 2 plexi, what are their names and what do they serve?
- Submucosal plexus –> submucosa and muscularis mucosa, 2. Myenteric plexus –> circular and longitudinal smooth muscle layers
Which nerve plexus is innervated by the ANS?
trick, they both are!
Sensory cells located in the epithelium feedback and target where?
Back to the brain but also to the 2 plexi in the Enteric NS
The Myenteric plexus is sandwiched by the 2 smooth muscle layers, which is closest to the lumen of the GI Tract?
Circular
Which smooth muscle is in charge of determining the depth of the rugae and convolutions of the mucosa?
Muscularis mucosa
Parasympathetic innervation on the Enteric NS is pre or post ganglionic?
PRE
Sympathetic innervation on the Enteric NS is pre or post ganglionic?
Mostly post
If parasympathetic innervation, the NT between pre ganglionic and post is?
ACh on nicotinic receptors.
Then these cells would release ACh onto muscarinic receptors to ever where they would be.
Sympathetic is already postganglionic, so the NT being released will be:
NE on adrenergic receptors (alpha1, alpha2, beta1, beta2)
The afferent information that is collected by sensory cells in the mucosa epithelia that is FEEDING BACK TO THE ENTERIC NS, is called:
the SHORT LOOP (local)
Afferent input from the mucosa that is FEEDING BACK to the BRAIN is called what? and does what?
the LONG LOOP - changes the balance between sympathetic and parasympathetic.
The sensory neurons in the mucosa have what kind of receptors to sense conditions?
Osmoreceptors and chemoreceptors
What nerves are supplying the autonomic input to the gut and where?
From epiglottis –> Left colic flexure = VAGAL, from there on = SACRAL SPINAL CORD
In general what is the Parasympathetic innervation doing in the gut?
INCREASE motility, RELAX sphincters, STIMULATE secretions
In general, what is the Sympathetic Innervation doing in the gut?
DECREASE motility, CONTRACT sphincters, INHIBIT secretions
What NTs are released by sensory neurons in mucosa which feedback on the SHORT LOOP to EXCITE enteric interneurons?
Substance P, CGRP
What NTs are released between ascending and descending interneurons in the MYENTERIC PLEXUS?
ACh, Serotonin (5-HT)
What NTS are released by secretomotor neurons in the mucosa that target the Submucosal plexus?
ACh, VIP
What do the chemoreceptors in the mucosa sense?
Osmolality, acid, nutrients
Motor neurons on the smooth muscle can be Excitatory or Inhibitory depending on what they release:
NO –> dilate –> INHIBIT, ACh –> constrict –> EXCITE
What kind of cells provide pacemaker activity to ENS?
Interstitial cells of CAJAL (ICC)
What is another name for the “basic electrical rhythm of the gut”?
Slow wave of depolarization
Can the ICC cells generate an AP by themselves?
No, need ANS innervation
Once the pacemaker cells are innervated by the ANS, how does the AP spread from cell to cell?
Via gap junctions, will share the SINGLE DEPOLARIZATION
Where are gap junctions and shared depolarizations NOT found?
Esophagus and gall bladder
Which has a faster pace the stomach or the small intestine?
Duodenum is 12/min, stomach is 3/min
Describe peristalsis contraction in the STOMACH?
Waves of contraction from pacemaker site (below fundus) towards the PYLORUS. Once hit pylorus then will come back in other direction
Which ANS tract INCREASES the the amplitude of action potentials stimulating the ICC?
PARASYMPATHETIC = increased motility
What is going on with the circular and longitudinal muscles during PERISTALSIS?
CONTRACT longitudinal while DILATE circular and vice versa –> PROPULSION
Upstream motor neurons you want to _______ and downstream motor neurons you want to _______.
CONSTRICT upstream, INHIBIT downstream
Why do you have GI dysfunction while taking viagra?
NO –> inhibits and dilates muscles (not much contraction)
Receptors in pharyngeal wall stimulated by BOLUS and sends afferent signals to:
BRAINSTEM SWALLOWING CENTER
What does the brainstem do in response to the afferent message?
Initiates COORDINATED efferent output to muscles of tongue, palate, pharynx, larynx, and esophagus.
What is a consequence of not being able to coordinate swallowing mechanisms?
Regurgitation, Airway asphyxiation
T/F. the esophagus sends AP via Gap Junctions?
FALSE!!! It’s sequential, each one has its own ANS innervation
How many seconds does it take each wave of esophagus to reach the stomach?
9 seconds
What happens if you don’t swallow a pill on the first swallow?
Local afferents generate a stronger impulse and get it on second swallow
Abnormalities of swallowing REFLEX?
DYSPHAGIA
Prolonged relaxation of lower esophageal sphincter?
GERD
Lower sphincter not opening fully?
Achalsia
How do the different compartments of the stomach differ in digestion?
Proximal = Reservoir, Distal = grinds food
T/F. LOngitudinal muscles are the “gatekeepers” into the SI from stomach?
FALSE! Circular are. Some longitudinal muscles are continuous to the SI
What controls the size and amount of particles exiting the stomach?
PYLORUS
How is gastric rate slowed?
Via STRETCH receptors and MECHANO and CHEMO receptors via CCK –> feedbacks to vagus
Describe how the OSMO-receptors at the PYLORUS determine gastric emptying?
IF thinks it can absorb it quickly (sugar water) then would let it right through. If chunky and hard to absorb then would keep closed and send it back up for more grinding.
How do NTs affect the Pyloric sphincter?
NO –> relaxation –> SPEED UP, OPIODS or CCK –>contraction –> SLOW DOWN
In the absence of food, the stomach generates:
Migrating motor complexes (MMC)
What do the MMC do?
increases contractions to clear indigestible material into LI
What are some PATHOLOGIES of the pyloric sphincter?
Stenosis (due to projectile vomiting), Gastroparesis (intolerant of solid diet)
What are the sites of most digestion and absorption?
Duodenum and Jejunum
What’s transit time of the SI?
2-4 hours
How is the AP generated in the SI?
slow wave generated by ICC and passed they GAP JUNCTIONS
What is an ileus?
Lack of motility
What is mostly absorbed in the LI?
Water and salt
How are the gap junctions different in the LI?
Less of them
Intermittent contraction of circular muscles in LI, divides the colon into what?
Haustra
Which muscle type dominates in sigmoid colon and rectum?
Longitudinal
Traversing the LI takes how long?
1.5 days!
Why do we want the rate in the LI to be slow?
To absorb all water and salts
Besides absorbing water and salts, what is the other main job of the LI?
concentrate and store fecal matter
T/F. There are MMC in the LI
FALSE, but 3x a day, following a meal, and intense contraction, known as a MASS MOVEMENT, forces feces toward rectum.
How is contraction different in a mass movement in comparison to peristalsis?
Stay contracted for some time after a mass movement
Relaxation of internal sphincter is mediated by what NT?
VIP, NO
How is the external sphincter controlled?
anal sampling and voluntary control
What other things can trigger defecation?
Mechanical stretch (gas, fluid, mass), Standing in the morning, dietary triggers, smoking
What is the end point of mass movement?
DEFECATION
