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GI: Swallowing (deglutition) (Common Disorders (Diffuse Esophageal Spasm…
GI: Swallowing (deglutition)
Sphincters
general:
facilitates unidirectional movement thru-out GI tract
via coordination of other smooth m. contractions, neural stimulation & humoral stimulation
proximal stimuli (+) relaxation
distal stimuli (+) contraction
high resting pressure in order to maintain separation
muscular barriers
regulate anterograde & retrograde movement
Upper Esophageal Sphincter (UES)
closed during inspiration >> limits air entry into esophagus
skeletal m. >> regulated by cranial nn. from swallowing center
highest
resting pressure of GI sphincters
aka pharyngoesophageal sphincter
protects airway from swallowed material & gastric reflux
Lower Esophageal Sphincter (LES)
resting tone
normally tonically constricted >> prevents gastric refllux
set by intrinsic myogenic properties & cholinergic regulation
relaxation
intrinsic muscle properties
relaxes after UES returns to resting tone
when < intragastric pressure >> food enters stomach
VIP & NO relax sphincter by inhibiting vagus n.
swallowing/esophageal distention >> dec. LES pressure
aka gastroesophageal sphincter
also assisted by a valve-like mechanism of a portion of esophagus that extends slightly into stomach
smooth m.
Esophagus
Composition
upper 1/3 (UES): voluntary sk. m.
middle 1/3: mixed, sk & smooth m.
lower 1/3 (LES): involuntary, smooth m. (regulated by ANS & ENS plexus)
clears material refluxed from stomach
Common Disorders
GERD
gastroesopheal reflux disease; common
Barrett's esophagus
metaplasia: simple squamous to columnar epithelium
adaptation to chronic acid exposure
10-20% of patients w/ chronic GERD
predisposition to evolve into esophageal cancer
causes
heartburn
dec. salivary mucus & HCO3
irritates lining of esophagus
ulcers can form
LES does not work properly (leaks)
Dysphagia
difficulty swallowing
common in elderly
due to abnormalities in:
functional
abnormal swallowing reflex
d/t neuro or muscular defect
disease states
Myasthenia gravis
stroke
Parkinson's
neurological disorder
xerostomia
structural
diverticuli in esophagus
abnormal tongue
Achalasia
failure of LES to relax >> food retained at LES
special form of dysphagia
complete lack of peristalsis w/in esophagus
caused by:
nerve degeneration of ENS
lack of NO synthase, VIP
Chagas disease
: infectious protozoa
(
Trypanosoma cruzi
); triatomine bug is principle vector in S. America (Columbia, Venezuela, Guatemala, etc.)
bird's beak appearance of LES
on barium radiograph
risk of aspiration, choking, malnutrition
Incompetent LES
uncoordinated esophageal contraction
cause is unknown >> idiopathic
GERD is secondary to incompetent LES
failure of LES to contract
various drugs, hormones, neuro-humoral agents produce (+)/(-) effects on LES
cessation of ACh activity; release of NO/VIP
Diffuse Esophageal Spasm
normal amplitude contractions,
but uncoordinated, simultaneous, or rapidly propagated
food can become stuck in esophagus
symptoms
dysphagia
regurgiation
chest pain
very hot or cold foods may trigger episode
cause unknown
may be d/t disruption of swallowing reflex
corkscrew
appearance on radiograph
Hiatal Hernia
movement of LES & upper part of stomach into thoracic cavity
inc. GERD symptoms
thru tear or weakness in diaphragm
3 phases
Oral phase
initiated as voluntary swallowing
location: base of tongue >> pharynx
tongue pushes bolus up & back against hard palate
once started, becomes almost entirely automatic & cannot be stopped
Pharyngeal phase
involuntary
stimulus:
trigeminal & glossopharyngeal nn. >> medulla oblongata (tractus solitarius) >>
swallowing >> (+) touch receptors around opening of pharynx (tonsillar pillars) >>
location: thru pharynx >> esophagus
MOA:
trachea & nose closed
soft palate elevated to block nasopharynx
vocal cords strongly approximated, larynx pulled superoanteriorly & epiglottis close larynx
esophagus open
upward larynx enlarges esophagus
UES relaxes >> remains strongly contracted b/w swallows
NS initiates fast peristaltic wave in pharynx
forces bolus into upper esophagus
deglutition center
(medulla & lower pons)
CNs V, IX, X, XII (& some superior cervical nn.) >> swallowing reflex
(-) respiratory center of medulla
Esophageal phase
involuntary
location: pharynx >> UES >> LES >> stomach
after UES closes, LES relaxes
primary peristalsis
continuation of pharyngeal peristaltic wave; begins below UES
both modulated by sensory fibers to CNS & ENS
secondary peristalsis
initiated by distension
only occurs if primary is not sufficient
modulated by sensory fibers to the CNS and ENS
initiated by:
pharyngeal reflexes >> vagal afferent fibers >> medulla >> glossopharyngeal & vagal efferent nn. >> esophagus
myenteric inhibitory neurons precede perstalsis >>
receptive gastric relaxation
reflex control
receptors: touch receptors near opening of pharynx
integration center: swallowing center near lower pons
effectors: pharyngeal & esophageal striated & smooth mm.
efferents
upper esophagus & pharynx
cranial nn.
lower esophagus
vagus n.