Learning Objectives
- Identify the anatomical course and vertebral levels (C6 to T11) of the oesophagus.
- Distinguish the histological transitions in the muscularis externa (striated vs. smooth muscle).
- Master the four physiological constrictions (ABCD) and their clinical significance.
- Analyze the portosystemic anastomosis and its role in oesophageal varices.
- Understand the metaplastic changes associated with Barrett’s Oesophagus.
Anatomical Course & Sphincters
The oesophagus is a 25cm fibromuscular tube transporting food from the pharynx to the stomach.
- Origin: Inferior border of cricoid cartilage (C6).
- Hiatus: Enters the diaphragm at T10 (Right crus).
- Termination: Cardiac orifice of the stomach at T11.
Sphincters
- Upper Oesophageal Sphincter: Anatomical sphincter formed by the cricopharyngeus muscle.
- Lower Oesophageal Sphincter: Physiological (functional) sphincter. Maintained by the acute angle of entry, mucosal folds, and the “pinch-cock” effect of the diaphragm.
Histology and Muscle Composition
The muscle layer transitions from voluntary to involuntary control as it descends:
| Oesophageal Third | Muscle Type | Innervation Source |
|---|---|---|
| Superior 1/3 | Voluntary Striated Muscle | Nucleus Ambiguus (Vagus) |
| Middle 1/3 | Mixed Striated & Smooth | Mixed |
| Inferior 1/3 | Involuntary Smooth Muscle | Dorsal Motor Nucleus (Vagus) |
Physiological Constrictions (Mnemonic: ABCD)
These are sites where foreign bodies are most likely to obstruct:
- A – Arch of Aorta
- B – Bronchus (Left main stem)
- C – Cricoid cartilage (C6)
- D – Diaphragmatic hiatus (T10)
Vasculature and Portosystemic Anastomosis
The abdominal oesophagus is a critical site for portosystemic communication.
- Arterial: Upper (Inferior thyroid a.), Middle (Thoracic aorta), Lower (Left gastric a.).
- Venous Anastomosis: Connection between the Left Gastric Vein (Portal) and the Azygous Vein (Systemic).
- Clinical Pearl: Portal hypertension (e.g., in cirrhosis) causes backflow into this anastomosis, leading to Oesophageal Varices, which carry a high risk of life-threatening haematemesis.
Clinical Correlations
- Barrett’s Oesophagus: Metaplasia of lower epithelium from stratified squamous to gastric columnar due to chronic GERD.
- Adenocarcinoma: Malignancy occurring in the lower 1/3, strongly associated with Barrett’s.
- Squamous Cell Carcinoma: The most common global subtype; can occur at any level.
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