Oesophagus Anatomy
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Direct answer
Swallowed food crosses three narrows in a 25-centimetre tube running from the lower border of the cricoid cartilage (C6) to the cardiac orifice of the stomach (T10-T11): the cricopharyngeus constriction 15 centimetres from the incisors, the arch-and-left-bronchus constriction at 22.5, and the diaphragmatic narrowing at 40 — the endoscopist's three numbers. Its muscle is striated in the upper third, mixed in the middle and smooth in the lower; its blood supply arrives in three territories — inferior thyroid artery in the neck, aortic branches in the thorax and the left gastric artery in the abdomen — and that third territory is a portosystemic anastomosis, which is why cirrhosis bloom varices at the lower end. The recurrent laryngeal nerves run in its grooves, the thoracic duct climbs behind it, and the left atrium presses on it in front.
What you must remember
- Constrictions with distances: cricopharyngeus (upper sphincter) at 15 cm, aortic arch and left main bronchus at 22.5 cm, diaphragmatic at 40 cm — the narrowest is the first, where swallowed coins and dentures impact.
- Relations that matter: trachea and recurrent laryngeal nerves in front; vertebral column, thoracic duct and azygos behind; the arch and left main bronchus crossing at 22.5 cm; the left atrium's impression lower down.
- Blood territories: cervical — inferior thyroid; thoracic — oesophageal branches of the descending aorta; abdominal — left gastric (from the coeliac axis). The left gastric territory drains to the portal system: the lower-end anastomosis.
- Varices: at the gastro-oesophageal junction, oesophageal (portal) veins meet systemic drains; portal hypertension converts them into varices just above the junction — the commonest cause of upper gastrointestinal bleeding in Indian cirrhotics.
- Nerve supply: recurrent laryngeal nerves to the striated upper third including cricopharyngeus; vagal trunks and the enteric plexuses to the smooth muscle below — which is why vagal injury above affects the upper tube.
- Sphincters: the upper is anatomical (cricopharyngeus); the lower is physiological — no discrete anatomical sphincter exists, only the diaphragmatic pinch, the angle of His and the phreno-oesophageal ligament.
- Diverticula and dysmotility: Zenker's pouch pulsates through Killian's dehiscence above cricopharyngeus; achalasia, the failure of the lower end to relax, gives the bird-beak radiograph and food regurgitation.
Following the endoscope's numbers
The endoscopist reads the oesophagus in centimetres from the upper incisors, and each number is an anatomy lesson. At 15 the scope meets resistance — cricopharyngeus, the striated upper sphincter; just above it is Killian's triangle, where a Zenker's diverticulum pouches out — regurgitation of undigested food, halitosis, aspiration. At 22.5 the lumen deviates as the aortic arch and left main bronchus indent it — the landmark where an impacted foreign body or the second ring of a tumour sits, and where perforation threatens both great vessels and airway. At 40 the pink squamous lining gives way to columnar gastric mucosa across the zig-zag line; in the cirrhotic patient it is here that varices snake up as red cords, and elsewhere in the same patient the portal-systemic map explains the caput medusae and haemorrhoids — one haemodynamic problem expressed at three anatomical sites, of which the oesophageal bleeds first and worst.
Where students slip
The classic error is naming the narrowest point as the diaphragmatic opening; it is the cricopharyngeus, and that is why a swallowed coin in a child lodges at the very top. The second slip is the muscle pattern — upper third striated, middle mixed, lower smooth — which the examiner converts into a nerve question: the striated segment depends on the recurrent laryngeal and other vagal branches, so a high vagal injury disturbs initiation of swallowing, not just gastric function. The third is the left atrial relation: the posterior indentation on barium swallow was the old evidence of mitral stenosis — still asked in Indian vivas.
Frequently asked questions
What are the three constrictions of the oesophagus and their distances from the incisors?
The cricopharyngeus at 15 cm, the aortic arch and left main bronchus at 22.5 cm, and the diaphragmatic opening at 40 cm. The uppermost, cricopharyngeus, is the narrowest point of all.
Where is the portosystemic anastomosis in the oesophagus?
At the lower end, where oesophageal veins draining to the azygos (systemic) meet left gastric tributaries (portal). Portal hypertension dilates them into varices just above the gastro-oesophageal junction.
How does the muscle and nerve supply change along the oesophagus?
The upper third is striated, supplied by the recurrent laryngeal and vagus; the middle third is mixed; the lower third is smooth, governed by vagal and enteric plexuses. Cricopharyngeus itself is striated.
What is a Zenker's diverticulum?
A pulsion diverticulum through Killian's dehiscence, the weak triangle above cricopharyngeus between its transverse and oblique fibres. It presents in the elderly with regurgitation of undigested food, gurgling and aspiration.
Why does an enlarged left atrium matter to the oesophagus?
The left atrium lies directly in front of the oesophagus at about T5-T7 and indents it. This relation allowed barium swallow to demonstrate mitral stenosis and is now used for transoesophageal echocardiography.