Gastro-oesphageal Re ux Prevention
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1) Lower oesophageal sphincter muscle
Not a distinct anatomic structure, rather a zone of high pressure located in the lower end of the
oesophagus.
• 3-4cm in length (re ux if length <2cm)
• Maintains pressure 10-25mmHg (GERD if pressure < 6mmHg)
• Derived from the inner circular layer of lower oesophagus - exists in state of tonic contraction
• Sling bres of gastric cardia - oriented diagonally from the cardia- fundus junction to the
lesser curve of the stomach
• Pinch-cock mechanism of diaphragm on inspiration - inspiration, when intrathoracic pressure
decreases relative to intra-abdominal pressure, the AP diameter of the crural opening is
decreased, compressing the esophagus and increasing the measured pressure at the LES.
• Maintenance of LES by phreno-oesophageal ligament → muscular bres (septum
transversum) of diaphragm, collar of Helvetius holds the LES in position.
• Transient lower oesophageal sphincter relaxation - i) part of swallowing mechanism, ii)
associated with distended stomach to allow venting of stomach gas, iii) allows vomiting →
dysfunction leads to re ux
2) Length of abdominal portion of oesophagus
• Intrabdominal length 3.5-4cm; length of 1cm
associated 81% re ux occurrence
3) Angle of His
• Acute angle where oesophagus enters stomach at
gastro-oesophageal junction
• Mucosa folded upon itself, rosette like
con guration esp in presence of increased
intraabdominal pressure or decreased intrathoracic
pressure
4) Increased intraabdominal pressure - increased intraabdominal pressure is transmitted to the GEJ, which
increases the pressure on the distal oesophagus and
prevents spontaneous re ux of gastric contents.
5) Clearing oesophageal re uxate - oesophageal peristalsis
Saliva
Volume 1-1.5L, ph 7
Components
• Water
• Electrolytes (↓ Na 40, Cl 40, ↑K 20, HCO3
50)
• Enzymes (salivary amylase/ ptyalin →
parotid gland, lingual lipase → Ebner’s
glands posterior tongue)
• Mucin (submandibular, sublingual glands)
• Proline rich uid - protects enamel
• IgA antibodies
• Lysosyme, lactoferrin, thiocyanate ions
Formation of saliva - primary and secondary
active secretion
active reabsorption
passive reabsorption
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passive secretion
PHYSIOLOGY
Deglutition
Mastication
• Performed in the oral cavity (limits: oral vestibule to palatoglossal arch posteriorly)
• Mechanical debulking of ingested food → i) breaks down cellulose bres of fruits and
vegetables ii) increases surface area for digestive enzymes iii) prevents excoriation of rest of
digestive tract
• Muscles of mastication important → presence of food bolus → stimulation of contraction of
muscles that cause mandibular depression → jaw drops stimulates stretch re ex of muscle
spindle bers → sends a erent bres via CN V3 → e erent bres to antagonistic muscles →
re ex elevation → chewing and crushing food.
• Once mandible elevates → stimulation of pressure receptors on jaw → sends a erent bres to
brainstem → inhibitory motor signals to mandibular elevators → mandibular depression
• Mandibular depression (lateral pterygoid- CN V3, anterior belly digastric- CN V3, mylohyoid CN V3, geniohyoid - C1 cervical plexus)
• Muscles of mandibular elevation (masseter, temporalis, medial pterygoid (CN V3)
• Salivary glands (intrinsic 10% and extrinsic 90%)
• Extrinsic - parotid (salivary amylase/ ptyalin), submandibular and sublingual (mucin)
• Lubricates food bolus, chemical digestion of food, acts as solvent to food molecule (helps
with taste)
Three phases of Swallowing: oral, pharyngeal, oesophageal
1) Oral - voluntary
• Tongue elevates (extrinisic muscles - styloglossus, genioglossus - CN XII) → formation of
central trough (intrinsic muscles - CN XII) → and pushes the food bolus upwards towards the
hard palate and posteriorly and downward to oropharynx
2) Pharyngeal - involuntary
Starts at the palatoglossal arch, lasts ~2 secs
• Presence of food in oropharynx stimulates nerve bres in palatoglossal arch/ palatopharyngeal
arch/ tonsillar pillars → sensory impulse to swallowing centre via CN V/ IX, motor bres return
to pharynx and oesophagus via CN V, IX, X, XII and few upper cervical spinal nerves
• To prevent aspiration of food into nasal cavity - closure of nasopharynx
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• E erent bres from CN X stimulates the uvula → contraction → elevation of uvula
• E erent bres of CN X stimulate levator veli palatini → contraction → elevation of the muscle
hence elevation of soft palate
• Eferent bres of CN V3 stimulate tensor veli palatini → tenses muscles →augments action of
LVP
• To prevent aspiration intro trachea:
• Vocal cords approximate - adduction → lateral cricoarytenoids and transverse arytenoids
contract
• Epiglottis moves inferiorly to cover glottis - retroversion
• To ensure food bolus passes into the pharynx
• Palatoglossal and palatopharyngeal folds are pulled medially forming slit through which
bolus can pass
• Pharynx pulled superiorly via outer longitudinal muscles → stylopharyngeus (CN IX),
salpingopharyngeus (CN X), palatopharyngeus (CN X)
• Pharyngeal peristalsis via superior, middle and inferior pharyngeal constrictors (inner circular
muscles)
• Suprahyoid muscles causes larynx to elevate and move anteriorly
• To ensure food passes into oesophagus
• Lower part of inferior pharyngeal constrictor is cricopharyngeus (CN X)→ upper
oesophageal sphincter relaxes and causes the bolus to transition to oesophagus
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3) Oesophageal - involuntary
• Primary peristalsis through oesophagus
• Secondary peristalsis initiated by stretch receptors → triggered by presence of food bolus in
oesophagus → distension of oesophagus → stimulation of stretch receptors of myenteric
plexus → stimulate circular bres above the bolus and inhibit longitudinal bres above the bolus
AND relaxation of stimulate longitudinal muscles below bolus and inhibit circular muscles below
bolus
• Mechanism of peristalsis: contraction of smooth muscle behind the bolus and relaxation of
smooth muscle in front
• Peristalsis moves moves 2-25cm/sec (relative to area of GIT, in oesophagus, 2-5cm/sec
• Relaxation of lower oesophageal sphincter