Esophagus: Anatomy and Physiology - MCh Surgery Level

1. Overview and Extent

• Resting lumen diameter: ~20 mm (can distend to 2 cm AP, 3 cm lateral)
• Total length (resting): 18-26 cm
• No serosa - this is a key surgical fact (contributes to anastomotic leak risk and early local tumor spread)

2. Segments and Anatomical Relations

Cervical Esophagus (C6 - Suprasternal notch, ~4-5 cm)

• Anterior: Trachea (left recurrent laryngeal nerve runs in tracheoesophageal groove - at surgical risk during cervical dissection)
• Posterior: Prevertebral fascia and vertebral column
• Lateral: Carotid sheaths and thyroid gland

Thoracic Esophagus (Suprasternal notch - Diaphragm)

• Divided into upper, middle, and lower thirds
• Upper thoracic: passes posterior to trachea, posterior to the left main bronchus
• At T4: crosses posterior to aortic arch
• At T5: crosses posterior to tracheal bifurcation and left main bronchus
• At T8: turns left and crosses anterior to the descending aorta
• At T10: passes through the diaphragmatic hiatus (through the right crus)

Abdominal Esophagus (0.5 - 2.5 cm)

• Anterior: Left lobe of liver
• Right: Caudate lobe of liver
• Left: Fundus of stomach
• Posterior: Right crus of diaphragm and aorta
• Compressed by intraabdominal positive pressure - contributes to LES function

3. Wall Layers (No Serosa - Surgical Significance)

Absence of Serosa - Surgical Implications

1. Anastomotic leak rates higher than bowel anastomoses
2. Tumor invades mediastinum earlier (T3 = adventitia involvement)
3. No natural barrier to prevent local spread
4. Requires extra care in anastomotic technique (submucosa is the holding layer)

4. Musculature

• Cricopharyngeus is C-shaped (no posterior midline raphe), attaches to lateral cricoid - this makes the posterior midline the natural weak point (Killian's dehiscence / Zenker's diverticulum).

5. Blood Supply (Segmental, Surgically Critical)

• Blood supply is segmental with limited overlap - esophageal infarction is rare due to submucosal anastomotic network, but devascularization during extensive mobilization risks ischemic anastomotic leak
• The left gastric artery (branch of celiac axis) is the dominant supply to the GEJ - must be preserved when doing Heller myotomy or sacrificed deliberately in esophageal cancer resection with gastric pull-up

6. Venous Drainage

7. Lymphatic Drainage (Non-Segmental - Surgical Significance)

• "Skip lesions" - tumors can spread to nodes far from the primary site
• Most esophageal cancers have lymph node spread beyond the primary region at time of diagnosis
• Need for extended lymphadenectomy (2-field or 3-field) in esophageal cancer resection

8. Nerve Supply

Motor (Vagus - Parasympathetic)

• Nucleus ambiguus (NA): innervates UES and upper esophageal striated muscle via recurrent laryngeal nerves
• Dorsal motor nucleus (DMN): innervates smooth muscle of lower esophagus and LES via esophageal plexus
• At the level of the diaphragm, the esophageal plexus condenses into:
  • Anterior vagal trunk (predominantly left vagus) → anterior gastric branches + hepatic branch
  • Posterior vagal trunk (predominantly right vagus) → posterior gastric branches + celiac plexus branch
• Vagal rotation: During gut rotation, the left vagus moves anteriorly and the right moves posteriorly (rotate clockwise when viewed from above)

Sympathetic

• Superior cervical ganglion, thoracic sympathetic chain, major splanchnic nerve, celiac ganglion
• Mediates nociception (pain) from the esophagus

Enteric Nervous System

• Meissner plexus (submucosal): parasympathetic ganglia - secretomotor
• Auerbach (myenteric) plexus (between inner circular and outer longitudinal): coordinates peristalsis

9. Sphincters

Upper Esophageal Sphincter (UES)

• Anatomic structures: Cricopharyngeus muscle (primary) + inferior pharyngeal constrictor + thyropharyngeus
• Located at C5-C6 level
• Manometrically: 2-3 cm zone of high pressure
• Resting tone: tonic contraction at ~100 mmHg (prevents air entry during respiration)
• Relaxation: during swallowing - passive by laryngeal elevation opening the sphincter actively
• Cricopharyngeus is a C-shaped muscle (no dorsal raphe) - Killian's triangle (posterior midline weakness) predisposes to Zenker's diverticulum

Lower Esophageal Sphincter (LES)

• NOT a true anatomic sphincter - it is a 3-4 cm zone of high pressure (15-25 mmHg resting) at the GEJ, extending 1-2 cm above and below the diaphragm
• A functional/physiological sphincter created by:
  1. Intrinsic smooth muscle tone (dominant mechanism)
  2. Angle of His (oblique angle of esophagogastric junction)
  3. Diaphragmatic crura acting as an external squeeze during inspiration
  4. Phrenoesophageal ligament (Laimer's membrane)
  5. Intraabdominal positive pressure on abdominal esophageal segment
• Factors increasing LES tone (prevent reflux): gastrin, motilin, substance P, alpha-adrenergic agonists, metoclopramide, acetylcholine
• Factors decreasing LES tone (cause reflux): secretin, CCK, VIP, nitric oxide, beta-agonists, nitrates, calcium channel blockers, alcohol, fat
• In hiatal hernia, the crural support and angle of His are disrupted → LES incompetence → GERD

10. Physiology of Swallowing

Three Phases

• Mastication, bolus formation, mixing with saliva
• Bolus pressed against faucial arches triggers pharyngeal phase
• CN IX and X afferents to brainstem swallowing center

• Soft palate elevation (seals nasopharynx)
• Laryngeal elevation + epiglottic tilt (airway protection)
• Pharyngeal constrictor peristalsis
• UES relaxation (active dilation by laryngeal elevation)

• Primary peristalsis: physiologic sequential constriction propagating at 2-4 cm/sec - propels bolus to stomach
• Secondary peristalsis: triggered by esophageal distension (not by swallowing) - clears residual food/acid
• Tertiary contractions: non-peristaltic, non-propulsive simultaneous contractions - abnormal (seen in presbyesophagus, DES)

11. Key Surgical Points Summary (MCh relevance)