1

Describe the anatomical course of the oesophagus (Figure 1)

The oesophagus is a muscular tube (approximately 25cm in length) that:

a)

extends from the pharynx at the lower border of the cricoid cartilage (at the level of the C6 vertebra);

b)

descends along the front of the vertebral column, through the superior and posterior mediastinum;

c)

passes through the diaphragm (at the level of the T10 vertebra);

d)

ends at the cardiac orifice of the stomach (at the level of the T11 vertebra).

2

Describe the anatomical layers of the oesophagus (Figure 2)

The oesophagus has four layers:

a)

adventitia;

b)

muscular layer (tunica muscularis) – which is composed of inner circular and outer longitudinal muscle fibres;

c)

submucosal or areolar layer – which contains blood vessels, nerves and mucous glands;

d)

internal mucosal layer (tunica mucosa) – which is composed of longitudinal folds that disappear on distension of the oesophagus and is covered with stratified squamous epithelium.

The muscular layer of the upper one-third of the oesophagus is striated muscle, with the lower one-third having smooth muscle and the middle one-third mixed striated and smooth muscle.

3

Describe the nerve supply of the oesophagus

The striated muscle part of the oesophagus is innervated by somatic neurones originating from the nucleus ambiguus, which travel within the vagus nerve.

The smooth muscle of the oesophagus is innervated by fibres originating from the dorsal motor nucleus of the vagus.

There are two neural plexi within the body of the oesophageal wall:

a)

myenteric plexus (Auerbach’s plexus) – which lies between the circular and longitudinal muscular layers and contains both parasympathetic vagal fibres and sympathetic fibres (from the cervical and thoracic sympathetic ganglia) to supply both layers of the tunica muscularis;

b)

submucosal plexus (Meissner’s plexus) – which lies within the submucosal layer of the oesophageal wall and contains only parasympathetic fibres to provide secretomotor innervation to the nearby oesophageal mucosa.

4

Describe the physiological components of the oesophagus

The oesophagus is divided into three physiologically distinct neuromuscular units:

a)

upper oesophageal sphincter (UOS) – which is defined as the 2-4cm zone of elevated pressure located at the junction of the pharynx and oesophagus and is formed from the striated muscle of cricopharyngeus and inferior pharyngeal constrictor;

b)

body of the oesophagus – which is an approximately 20cm muscular tube that extends from the caudal extent of the cricopharyngeus to the proximal margin of the lower oesophageal sphincter;

c)

gastro-oesophageal junction (GOJ) – which is contracted at rest and composed of four muscular elements, including:

i)

intrinsic lower oesophageal sphincter (LOS) – which is defined anatomically as a thickened band of circular muscle that is tonically contracted at rest;

ii)

crural diaphragm – which allows the oesophagus to pass through and compresses the intra-abdominal oesophagus during breathing, coughing or straining. Contraction of the crural diaphragm prevents gastro-oesophageal reflux due to increases in intra-abdominal pressure;

iii)

‘clasp’ fibres – which represent a semicircle of transverse smooth muscle fibres that encompass half of the GOJ (adjacent to the lesser curve of the stomach);

iv)

‘gastric sling’ fibres – which represent a long band of obliquely oriented smooth muscle fibres that arch around half of the GOJ (adjacent to the greater curve of the stomach).

5

Describe the stages of normal swallowing

The initiation of swallowing is under conscious control but once the food bolus or fluid enters the oesophagus, an involuntary reflex mechanism takes place to initiate a peristaltic wave.

Oral stage (voluntary) – where the food bolus is rolled posteriorly into the pharynx by the tongue pushing upwards and backwards against the hard palate.

Pharyngeal phase (reflex) – where the:

a)

soft palate is pushed upwards (preventing the bolus entering the nose);

b)

vocal cords adduct and the larynx is pulled upwards against the epiglottis (preventing the bolus entering the trachea);

c)

tonically contracted cricopharyngeus relaxes to allow the bolus into the oesophagus.

Oesophageal phase (reflex) – which incudes:

a)

primary oesophageal peristalsis (see below);

b)

relaxation of the LOS.

6

What is peristalsis?

Peristalsis represents a progressive wave of unidirectional, involuntary, symmetrical, muscular contractions and relaxations, which propel intraluminal contents in an antegrade direction through the gastrointestinal tract.

Primary peristalsis occurs when a food bolus reaches the back of the pharynx and relaxation of the UOS allows the bolus to be propelled into the oesophagus. Once the food bolus has passed the UOS, it closes again and the food bolus is then propelled down the oesophagus by a peristaltic wave of muscle contraction, until it reaches the LOS, which relaxes allowing the food bolus to enter the stomach.

Secondary peristalsis occurs in the body of the oesophagus in response to content within the oesophagus that is not cleared by the primary peristaltic wave or in response to material refluxed into the oesophagus.

Tertiary peristalsis refers to non-propulsive, irregular contractions, which occur simultaneously at different levels of the oesophagus. They can occur in isolation or repetitively and can be elicited spontaneously or by swallowing. They have no known physiological role and occur more frequently in the elderly.

7

Describe the factors that control gastro-oesophageal competence (Figure 3)

Anatomical:

a)

crural muscle of the diaphragmatic hiatus;

b)

acute angle of His (normally 50°-60°) – which represents the angle between the oesophagus and its entry into the gastric cardia. It can result in a valve-like closure of the LOS when the stomach is full;

c)

mucosal rosette in the lower oesophagus;

d)

intra-abdominal length of the oesophagus and intra-abdominal pressure;

e)

phreno-oesophageal membrane – which is a reflection of the subdiaphragmatic fascia onto the transversalis fascia of the anterior abdominal wall that also encircles the oesophagus. It is mainly responsible for maintaining an intra-abdominal segment of oesophagus.

Physiological:

a)

tonic contraction of the LOS;

b)

effective oesophageal motility;

c)

effective gastric emptying.

8

What are the principles of standard oesophageal manometry (Figure 4)?

Either water-perfused or solid-state manometry catheters are used, with sensors at 5cm intervals.

The manometry catheter is passed through the nose into the stomach and slowly withdrawn (station pull-through technique).

At each level, the patient is asked to do a dry and wet swallow.

The following information can then be obtained and analysed:

a)

LOS length, pressure, relaxation and intra-abdominal length;

b)

pressure inversion point (PIP);

c)

UOS length, pressure and relaxation;

d)

peristalsis wave progression throughout the length of the oesophagus;

e)

distal peristalsis wave amplitude (3 and 8cm above the LOS).