2.01 Swallowing and Motility Flashcards
saliva helps to form a bolus with what key components?
water, electrolytes, enzymes (amylase), mucins
what do the lingual lipase and alpha amylase enzymes in saliva digest respectively?
initial triglycerides and starch
what kind of reflex is swallowing?
parasympathetic
what are the three main phases of swallowing?
oral, pharyngeal, and esophageal
what phases of swallowing are involuntary and controlled by the brainstem?
pharyngeal and esophageal
How is the upper 1/3 of esophagus innervated and muscle makeup?
striated (somatic), via CN IX and CNX
How is the lower 2/3 of esophagus innervated and muscle makeup?
smooth muscle (ENS & ANS) CNX
during esophageal peristalsis how is the process alternating and generating pressure to move bolus?
contract above generating positive pressure to push bolus into relaxed portion below with negative pressure
What is the LES doing under normal conditions?
contracted to maintain high pressure barrier (sympathetic innervation)
how is the peristalsis contraction wave triggered?
presence of bolus in UES decreasing the pressure + neuronal response leading to the LES relaxing a bit
What is the baseline pressure of the UES, esophageal body, and LES?
UES and LES = high to maintain contraction (closed sphincter)
esophageal body is relatively low
What happens once you swallow to the LES baseline pressure?
it falls (muscle relaxes) to pass bolus and steadily increases to high resting pressure
Why does the UES in particular have such a quick spike up in baseline pressure faster swallowing?
to prevent backflow of bolus/content to the pharynx
swallowing initiates what response from brainstem?
vagal CNX
Key NT needed to relax LES?
NO and VIP
what state does the sphincter muscle have to be in to allow LES relaxation?
hyperpolarization
What is the neuronal pathways to relax the LES? (PARA)
extrinsic vagal response
(pregang vag) myenteric plexus synapse
Ach to N2 receptors on inhibit motor neurons (post gang) that release NO and VIP that bind to sGC and VAPC1 to hyperpolarize the PDGFR a+ cell to cause smooth muscles hyperpolarization (or directly)
What are the neuronal pathways to relax the LES? (PARA)
ENS/INTRINSIC response
descending IPAN
Ach - N2
descending interneuron* (+/-)
Ach - N2 receptor
inhibit motor neuron
PDGFRa+ - NO and VIP release to sGC and VAPC
smooth muscle cell relax
What is the neuronal tone pathway for normal tone of the LES?
thoracolumbar pre gang (T5-L2)
prevertebral celiac ganglia Ach to N2
post ganglionic NE to B2 (esophageal body relax) or a1 (LES contract) at myenteric plexus varicosities
Failure for the LES to relax leading to dysphagia is called?
Achalasia
What is a common cause/dysfunction found in achalasia?
dysfunction of post ganglionic inhibitory motor nuerons
GERD is associated with what problem to the LES?
spontaneous relaxation of LES that leads to very low (<5) resting pressure and retrograde flow of gastric contents
What common drug is known to relax smooth muscle and potentially lead to GERD symptoms? What condition?
CCB for HTN
blocks calcium needed in smooth muscle cells to relax
What can cause a hypotensive LES?
inadequate barrier function, reflux trigger sensitivity, mucosal damage
GI symptoms of chagas targets what part of LES that can lead to a megaesophagus?
destruction of neurons in the submucosal and myenteric plexus - LES cant relax and accumulates pressure
Do ICCs create action potentials?
NO, they make slow wave potentials that move rhymical via ion channels that precede an AP and typically cannot trigger itself (smooth muscle contraction)
Distention of the gut with a food bolus leads activates what via stretch?
IPAN (excitatory) nerves
What is being release alongside ICC to raise the threshold to activate an AP to trigger smooth muscle contraction?
Ach and SubP
What are the unique characteristics of slow wave membrane potentials when at rest, stimulated, or inhibited at the GI tract?
Rest = slow waves and some spikes = some muscle tone
stimulated = more slow waves, more spikes = more muscle tone
inhibited = less slow waves, no spikes = no muscle tone
what are the frequency GI contractions of the stomach?
3-5 contract/min
what are the frequency GI contractions of the small intestine?
12-20 contract/min
what are the frequency GI contractions of the large intestine?
6-8 contract/min
what generally can help depolarize membrane for GI contraction?
stretched muscle
parasympathetic stim
Ach
what generally can help REpolarize membrane for GI contraction?
NE
sympathetic stim
