The gullet (Greek 'oesophagus') is a hollow organ, approximately 25 cm long, assigned the task of actively sending our food to the stomach. The following article will provide you with a compact overview of the anatomy as well as the most important diseases of this organ and explains the physiology of the act of swallowing in understandable steps.

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Esphagus

Pivture: The esophagus (yellow) passes behind the trachea and the heart by ZooFari. Licence: (CC BY-SA 3.0)


Location of the Esophagus

The esophagus is a long, tube-shaped organ that sends our foods and fluids to the stomach by means of peristaltic movements. It begins at the same height as the 6th/7th cervical vertebrae, on the lower edge of the cricoid cartilage.

It begins with the superior esophageal sphincter at the bottom of the hypopharynx (or throat) adjacent to the left pyriform sinus, runs dorsal to the trachea in the chest area and ventral to the spine, continues in a caudal fashion through the diaphragm and ultimately ends at the junction with the cardia of the stomach, parallel to the 11th cervical vertebra. The esophagus has 2 gentle curves in the coronal plane. The first curve begins a little below its origin and inclines to the left all the way to the root of the neck and returns to the midline at the level of

The esophagus has 2 gentle curves in the coronal plane. The first curve begins a little below its origin and inclines to the left all the way to the root of the neck and returns to the midline at the level of fifth thoracic vertebra. In the chest, access to the esophagus can be gained from the right chest. The second curve to the left is formed as the esophagus bends to cross the descending thoracic aorta, before it pierces the diaphragm.

The esophagus also has anteroposterior curvatures that correspond to the curvatures of the cervical and thoracic part of the vertebral column.

Sections of the Esophagus

Pars cervicalis – begins at the cricoid, runs ventral to the spine, and after entering the chest cavity it becomes the:

Pars thoracica – longest section, runs dorsal to the trachea in the mediastinum, and after passing through the hiatus oesophageus of the diaphragm it becomes the:

Pars abdominalis – enters into the cardia of the stomach after about 1-3 cm.

The Three Constrictions of the Esophagus

Adjacent anatomical structures cause three constricted areas in the esophagus, which are called:

Constrictio cricoidea  is caused by the cricoid cartilage and is maintained constricted by the upper esophageal sphincter (UOS) until the sphincter relaxes in response to a bolus.

Constrictio partis thoracicae / aortal constriction  is caused by the proximity to the aortic arch (arcus aorta) and the left main bronchus

Constrictio diaphragmatica  is caused by the hiatus oesophageus of the diaphragm

Wall Structure of the Esophagus

The esophagus generally has the typical wall structure of the gastrointestinal tract. In terms of lamina, these are: mucosa, submucosa, muscular layer and the movable tunica submucosa as the outermost layer. The esophagus lacks a serial covering layer.

Layers_of_the_GI_Tract

Picture: Layers of the Alimentary Canal by Goran tek-en. Licence: (CC BY-SA 3.0)

Tunica mucosa (mucous membrane)

EsophagusLamina epithelialis mucosae

The innermost layer of the lamina consists of multi-layered, uncornificated squamous epithelium. It is subject to heavy mechanical strain.

Lamina propria mucosae

Loose conjunctive tissue with extensive venous plexus.

Side note on clinical presentations:

This venous plexus is important for portocaval anastomoses, e.g. with cirrhosis of the liver. If the portal system is under increased pressure, it finds already present anastomoses with the systemic circulation in which to dump blood to decrease that pressure. One of these connections is between gastric veins and esophageal veins. esophageal varices, dilated, thin walled and serpiginous veins may form, with the complication risk of rupture and massive upper intestinal hemorrhage – a life-threatening condition!

Lamina muscularis mucosae

Smooth muscle cells and the submucosal plexus (plexus submucosus)

Tela submucosa

  • Mucosal esophageal glands
  • Plexus submucosus
  • Extensive venous plexus

Tunica muscularis

The tunica muscularis consists of an interior circular layer (stratum circulare) and an external longitudinal layer (stratum longitudinale).

Between the circular and longitudinal layer is a portion of the enteric nervous system – the myenteric plexus (Plexus myentericus).

This controls the motility and peristalsis of the esophagus and the opening of the lower esophageal sphincter. The esophageal muscles are not uniform. The muscular fibers in the cranial part of the esophagus are red and consist chiefly of striated muscle; the intermediate part is mixed; and the lower part, with rare exceptions, contains only smooth muscle. Accessory bands of muscle connect the esophagus and the left pleura to the root of the left bronchus and the posterior of the pericardium.

Side note on clinical presentations:

Laimer’s triangle: This is a missing piece of longitudinal muscle in the dorsocranial area of the esophagus; this weak spot can lead to an increase in intraluminal pressure and an outward eversion of the mucosa and submucosa in the muscular layer. This is then called pseudodiverticulum. It was named in 1877 by German pathologist Friedrich Albert von Zenker, and is commonly caller Zener diverticulum. It can seen in elderly men complaining of regurgitation of undigested, malodorous food.

Note: True diverticula are eversions of all wall layers!

Tunica adventitia

The tunica adventitia is the shifting outer fascial layer that allows for free mobility of the esophagus while swallowing. It surrounds the esophagus and fills the spaces between the esophagus and surrounding organs, such as the trachea and bronchi, and the pleural. The following are located here:

  • the large supply vessels
  • lymphatic vessels
  • nerve fascicles of the vagus nerve and the esophageal plexus

Vascular Supply of the Esophagus

The three segments of the esophagus are supplied by various arteries.

Pars cervicalis – from the Inferior thyroid artery (from the truncus thyrocervicalis)

Pars thoracalis – from the aorta and the intercostal arteries

Pars abdominalis – from the oesophageales of the left gastric artery (from the truncus coeliacus)

Venous drainage occurs through the small v. oesophageales – into the v. azygos and v. hemiazygos – and into the superior v. cava.

Note: Collateral circulation – there are connections to the v. portae hepatis (portocaval anastomoses) through the v. gastrica dextra, which help prevent disruptions in blood drainage in the liver.

Lymph Discharge of the Esophagus

The lymphatic vessels generally follow the flow of the arteries. Lymph discharge also occurs through various lymph nodes depending on the segment of the esophagus.

The pars cervicalis deviates the lymph through the deep lymph nodes of the throat (nll. cervicales profundi) into the truncus jugularis.

The upper portion of the pars thoracica runs cranially through the mediastinal lymph nodes (nll. paratracheales, nll. tracheobronchiales superiores et inferiores) into the truncus bronchomediastinalis, while the lower portion of the pars thoracica, like the pars abdominalis (through the nll. gastrici sinistri et coeliaci) drains into the truncus intestinalis.

This joins with the cisterna chyli, which can be pictured as a sort of “reservoir”, from which the lymph flows solely in the ductus thoracicus into the left venous angle.

Innervation of the Esophagus

Like the other parts of the digestive system, the esophagus is mainly controlled by the autonomous/enteric nerve system, with the assistance of the parasympathetic and sympathetic nervous systems.

The sympathetic innervation occurs through post-ganglionic sympathetic fibres from the:

  • stellate ganglion the sympathetic trunk in the chest and the
  • Ganglia thoracica II-V (the post-ganglionic fibres of which extend into the plexus oesophageus)

Activation of the sympathetic nervous system causes inhibition of secretion of the oesophageal glands.

The parasympathetic innervation carries over in the upper esophageal segment of the n. laryngeus recurrens, and the lower portion of the esophagus is supplied by the n. vagus.

Beneath the bifurcatio tracheae, the left and right vagal trunks merge into the plexus oesophageus, from which the trunci vagales proceed in a distal manner, and pass through the hiatus oesophageales together with the esophagus.

Activation of the parasympathetic nervous system induces increase in gland secretion and heightened peristalsis.

Sensory Innervation

Afferent fibres containing the viscerosensory information of pain and stretching are led to the brain from the esophagus through the n.  laryngeus recurrens and the n. vagus.

The Closing Mechanism of the Esophagus

When resting, the esophageal muscles are exposed to greater longitudinal pressure, and the lumen is closed. (Resting pressure between 10-30 mmHg)

The esophagus possesses a closing mechanism at both its upper and lower end, which is are called the upper (UOS) and lower esophageal sphincter (LOS).

Upper esophageal sphincter (UOS)

It consists solely of striated skeletal muscles. Caudal segments of the m. constrictor pharyngis inferior, as well as a portion of the upper esophageal musculature, are part of its functional entity. The sphincter is innervated by the n. glossopharyngeus and the n. vagus. The upper esophageal sphyncter is a barrier against reflux and it prevents aerophagia.

Lower esophageal sphincter (LOS)

To be precise, this is not a true sphincter. Rather, various mechanisms interlock and form a functional entity that ultimately facilitates the sealing of the esophagus. Insufficient closing of the lower sphincter causes reflux of the stomach’s contents.

Clinical Presentations

Reflux is the return flow of gastric juices into the esophagus, which can become inflamed as a result (esophagitis).

Another complication of reflux disease is the peptic ulcer.

Chronic reflux induces a long-lasting state of irritation and can transform the multi-layered, uncornificated squamous epithelium into columnar epithelium. This restructuring of the tissue is called Barrett’s esophagus and is a precancerous condition because of its risk of degeneration.

The following mechanisms form the functional sealing entity of the lower sphincter:

  • Wringing mechanism – the smooth musculature in the tunica muscularis runs inward in a spiral shape along the caudal end of the esophagus
  • Angle of His – the esophagus joins with the cardia at an acute angle, which prevents reflux of gastric juices
  • Phreno-esophageal ligament – The ligament allows independent movement of the diaphragm and esophagus during respiration and swallowing.
  • Constriction effect of the diaphragm – the sides of the diaphragm muscle are located at the hiatus firmly around the esophagus
  • Venous plexus – extensive venous plexes are located in the mucosa (namely: lamina propria mucosae) and the submucosa

The LOS loosens reflexively (via the plexus myentericus), thereby allowing for the transit of food.

Functional disruptions of the sphyncter resulting from an insufficient opening lead to achalasia, which is described in detail in the section “Diseases of the esophagus”.

How does Swallowing Happen?

From an anatomical perspective, the swallowing of food and fluids is facilitated by a highly tensile, yet firmly established tissue in the esophagus.

The actual act of swallowing is a semi-reflexive process – i.e. controlling it is partially voluntary, partially involuntary. We willingly decide when we will swallow a bolus of nutrients. However, if it has touched the base of the tongue or the back of the throat, the swallow reflex is triggered and is involuntary, like every other reflex.

The swallowing process is subject to sensomotoric fine-tuning, meaning that it is adjusted to the consistency of the bolus. In this manner information on the scent, taste, texture and size of the bolus is constantly being sent to the brain. With more or less strong, peristaltic movements of the esophageal muscles, the food ultimately makes its way to the stomach.

When ingesting fluids, for instance, there are rarely any peristaltic movements of the esophagus. The upper and lower esophagus sphincters briefly open, while the base of the mouth and the tongue push the fluid down into the stomach via the so-called “splash swallow”.

The process is somewhat more complex for solid items.

We will divide the swallowing process into four different phases to illustrate how it works:

The oral preparation phase

serves to break down and insalivate the bolus – performed voluntarily

The oral transportation phase

includes closing of the lips and jaws, as well as the beginning of lifting of the velum to the nasopharynx – voluntarily triggered, reflexive process

 The pharyngeal phase

begins when the bolus has passed through the pharyngeal isthmus, and describes the transportation of the bolus through the pharynx while protected by the airways – reflexive (swallow reflex)

The esophageal phase

describes the transportation of the bolus through the esophagus into the stomach – reflexively controlled

Swallow Reflex

The broken down, insalivated bolus is passed over the tongue toward the pharynx. If the bolus makes contact with the base of the tongue or the back of the throat, afferents in the n. glossopharyngeus and the n. vagus lead the mechanical stimulation to the deglutition centre in the medulla oblongata – the pharyngeal muscles are subsequently activated.

During the swallowing process, the upper and lower airways are sealed, and respiration ceases.

Closing of the upper airways

The closing of the upper airways when swallowing is ensured by the so-called Passavant’s bar. The m. constrictor pharyngeus sup. contracts, thereby affecting a bulge-like swelling of the lateral and back epipharyngeal wall. Together with the backward motion of the velum, the bulge seals the nasopharynx while swallowing.

Trip to the clinic

If the velum is paralysed, as may be the case with diphtheria, this closing mechanism becomes insufficient, and food and fluids may enter the nose.

Closing of the lower airways

Closure of the vocal folds and epiglottis, the tightening of the base of the mouth and a larynx elevation – meaning that the larynx is lifted upward – causing a closure of the lower airways.

If the airways are secured, the upper esophageal sphincter opens via the n. vagus, and primary esophageal peristalsis is initiated.

The mid- and lower pharyngeal constrictor muscles contract, thereby moving the bolus to the esophagus. After the food has entered the esophagus, the UOS closes and the airways reopen.

The bolus now “slides” downward toward the stomach because of gravity, as well as the peristaltic motions of the esophageal muscles.

Esophageal Peristalsis

Primary esophageal peristalsis describes contractive waves of the esophageal muscles toward the LOS.

Secondary esophageal peristalsis is caused by the stretching of the esophageal wall induced by the bolus.

The LOS must relax for the bolus to enter the stomach, which occurs reflexively via the plexus myentericus.

LOS – tone is lowered by:

  • Secretin
  • Cholecystokinin
  • GIP (gastric inhibitory peptide)
  • Progesterone (pregnancy heartburn)

Note: A tone reduction of the LOS leads to insufficient closing, and thus to heartburn. Fat, alcohol, coffee and nicotine lower the muscle tone.

LOS – tone is increased by:

  • Motilin
  • Gastrin
  • Substance P

Note: Achalasia is a degenerative disease that leads to expansion of the esophagus upon insufficient relaxation of the LOS.

After entering the cardia, the LOS closes again. Passage of one bolus of solid food takes between 5 and 25 seconds.

Diseases of the Esophagus

Reflux disease = gastro-esophageal reflux disease = GERD

This widespread disease describes a chronic condition of increase reflux of gastric juices into the esophagus, which may lead to regurgitation, retrosternal pain and hoarseness.

As the mucous layer of the esophagus does not offer enough protection against the aggressive hydrochloric acid, the result may be esophagitis or even erosion (ulcers). The cause of reflux disease is a dysfunctional lower esophageal sphincter.

The reasons for weakness in muscle tone may be:

  • endogenous substances (e.g. progesterone during pregnancy)
  • toxins (alcohol, nicotine, caffeine)
  • poor nutrition (too much sugar and fat, carbonated beverages = “antacids”)
  • deficiency of vitamin B12
  • stress (via increase in the sympathetic nervous system)
  • increased pressure on the LOS/intra-abdominal (pregnancy, obesity, digestion problems, lying down)
  • hiatal hernias

Therapy is contingent on the triggering factors and primarily consists of removing these triggers. While simpler, stress-induced discomfort can often be improved by learning a relaxation procedure (e.g. PMR) and the avoidance of poor nutrition habits, surgery may be necessary for severe, chronic progression.

Furthermore, highly effective medications (antacids, H2 blockers proton-pump inhibitors = PPIs) are available.

Esophagitis

In this disease, the esophagus is inflamed due to a chronic state of irritation. Most of the causes lie in the long-term effects of noxes on the mucous and may come in many different forms:

  • HCL (gastro-esophageal reflux disease, constant vomiting from bulimia, etc.)
  • alcohol, high-percent – from alcohol abuse
  • mucous-damaging medication
  • infections (cytomegaly, herpes, candida, etc.)

Barrett’s Esophagus

Chronically untreated reflux disease many result in metaplasia of the esophageal epithelium, meaning that the normally multi-layered, uncornificated squamous epithelium is turned into columnar epithelium. This epithelium is resistant to stimulation, but is also susceptible to dysplasia, which may in turn become an early stage of cancer. For that reason, Barrett’s esophagus is also called precancerous.

Esophageal Cancer

This is the name for a malignant tumour the esophagus. This type of tumour is more frequent in patients exhibiting nicotine or alcohol abuse, as well as an overload of nitrosamines. Squamous epithelium carcinoma is more frequently encountered than adenocarcinoma.

Hiatal Hernia

Normally the esophageal hiatus  is constrained by the contraction of the diaphragm during inhalation. This ensures that no stomach contents enter the esophagus as a result of the intra-abdominal pressure increase during inhalation.

Regarding the hiatal hernia, the esophageal hiatus  forms a so-called hernial orifice, through which parts of the stomach or the entire stomach are permanently or temporarily displaced into the chest cavity. The cause of the hiatal hernia is the acquired expansion of the hiatus oesophageus.

This is abetted by the loss of the conjunctive tissue’s elasticity in old age, or the increase of intra-abdominal pressure, as is the case during pregnancy, obesity, chronic coughing, etc.

There are various types of hernias:

  • sliding hernias (axial hernias)
  • paraesophageal hernias
  • hybrids
  • upside-down stomach

Depending on the type of hernia, the functioning of the lower esophageal sphincter may be disrupted, and this may result in heartburn with all after-effects. The paraesophageal hernias often cause a feeling of pressure in the heart area, or shortness of breath, and have a high rate of complication – esophageal / gastral incarceration, twisted stomach, or similar. Paraesophageal hernias must be treated surgically due to the high rate of complication.

Esophageal Varices

With congestion of the portal vein, e.g. resulting from cirrhosis of the liver, the blood must be deviated through a circumventing route (portocaval anastomoses). One of these anastomoses deviates through the esophageal veins:

Vena portae hepatis

→ Venae gastricae

→ Venae oesophagea

→ Vena azygos/ V. hemiazygos

→ Vena cava superior

This may result in expansion of the vv. oesophagea – the esophageal varices. Rupture of the varices is associated with haematemesis and is an absolute emergency!

Diverticula

Pulsation diverticulum / pseudo-diverticulum

This type of diverticulum forms via dilation in the mucosa and submucosa in the esophagus in the weak area of the Laimer’s triangle.

Traction diverticulum / true diverticulum

These diverticula form in adjacent structures of the esophagus, regardless of muscular weak areas (e.g. parabronchial diverticula, epiphrenic diverticula).

Foetor ex ore and dysphagia are common. This may especially result in regurgitation and aspiration during the night. Diverticula can easily become inflamed or form fistulae with the accumulation of food remains.

Achalasia

A damaged plexus myentericus leads to a disruption of esophageal peristalsis and insufficient slackening of the lower sphincter, resulting in the typical “champagne glass” dilation of the esophagus.

Patients complain about difficulties swallowing, regurgitation and a feeling of retrosternal pressure.

Popular Exam Questions on the Esophagus

The solutions are found beneath the bibliography.

1. The tone of the lower esophageal sphincter is lowered by:

  1. Secretin
  2. Motilin
  3. Oestrogen
  4. Gastrin
  5. Substance P

2. Peristalsis of the esophagus is controlled by the

  1. Plexus myentericus
  2. Plexus submucosus
  3. Meissner’s plexus
  4. glossopharyngeus

3. The so-called Laimer’s triangle

  1. leads to achalasia
  2. forms varices in the esophagus
  3. is the cause of Barrett’s esophagus
  4. can form traction diverticula
  5. is a missing piece of longitudinal muscle in the dorsocranial area of the esophagus
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