Esophagus

The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. The wall of the esophagus is made up of 4 primary layers: mucosa (lined with squamous epithelium), submucosa, a thicker muscularis layer, and an outer layer of connective tissue. The esophagus also has a sphincter at each end, which allows it to help control the passage of food into the stomach.

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Development

Embryologic development of the esophagus:

  • Begins forming in the 4th week of development
  • Derived from the foregut of the primitive gut tube (an invagination of the yolk sac into the embryo)
  • Has components of endoderm and mesoderm:
    • Endoderm: forms the lining of the entire digestive tract, including the esophagus
    • Splanchnic mesoderm forms:
      • Muscle components of the esophagus
      • Connective tissue
Embryonic development of the gut tube

Embryonic development of the gut tube

Image by Lecturio. License: CC BY-NC-SA 4.0

Gross Anatomy

General characteristics and location

  • A long muscular tube connecting the pharynx to the stomach
  • Extends from C6 to T11 vertebra
  • Size:
    • Length: approximately 25 cm 
    • Diameter: approximately 2 cm when relaxed
  • Sections of the esophagus:
    • Cervical: travels through the neck, behind the trachea 
    • Thoracic: located in the mediastinum, between the heart and the vertebrae
    • Abdominal: located below the diaphragm, within the abdominal cavity
Location of the esophagus

Location of the esophagus

Image by Lecturio.

Cervical part (pars cervicalis)

  • Located within the neck, in direct connection with the pharynx
  • Length: approximately 5 cm
  • Upper border of the cervical part: lower edge of the cricoid cartilage (at C6)
    • Known as the pharyngoesophageal junction
    • Upper esophageal sphincter (UES): 
      • Made up of several muscles, most importantly the cricopharyngeus muscle
      • Surrounds the pharyngoesophageal junction
      • Helps control the passage of food into the esophagus from the pharynx
  • Lower border of the cervical part: the thoracic inlet and sternal notch (at T1)
  • Anatomic relations: 
    • Anterior: trachea 
    • Anterolateral: thyroid 
    • Lateral: carotid sheath
    • Posterior: vertebrae

Thoracic part (pars thoracica)

  • Located in the thorax between the trachea and the aorta
  • Length: 17–19 centimeters
  • Upper border: the thoracic inlet and sternal notch (at T1)
  • Lower border: 
    • Diaphragm
    • Passes into the upper abdominal cavity through the the esophageal hiatus (a hole in the diaphragm also called the esophageal foramen) at the level of T10
  • Anatomic relations:
    • Structures anterior to the thoracic esophagus: 
      • Trachea and left main bronchus
      • Ascending aorta and aortic arch 
      • Left atrium
      • Anterior vagus nerve
    • Structures posterior to the esophagus: 
      • Descending aorta
      • Thoracic vertebra 
      • Thoracic duct (to the left of the esophagus)
      • Azygos and hemiazygos veins 
      • Posterior vagal nerve

Abdominal part (pars abdominalis)

  • Located within the abdominal cavity between the diaphragm and the stomach
  • Length: 1–3 cm
  • Curves sharply to the left to join the cardiac portion of the stomach
  • Upper border: 
    • The esophageal hiatus of the diaphragm (at T10)
    • Phrenoesophageal membrane: anchors the esophagus to the diaphragm
  • Lower border: the cardiac orifice of the stomach (at T11)
    • Known as the gastroesophageal (GE) junction
    • Lower esophageal sphincter: 
      • Surrounds the GE junction
      • Thickening of the circular muscle layer
      • Allows food into the stomach
      • Prevents reflux of stomach contents into the esophagus
  • Anatomic relations:
    • Anterior: liver
    • Posterior: descending aorta 
    • Right border: continuous with the lesser curvature of the stomach
    • Left border: separated from the fundus of the stomach by the cardiac notch
  • Relationship to peritoneum:
    • Covered by parietal peritoneum
    • Retroperitoneal

Constrictions

Constrictions are normal narrowings in the esophagus tube.

  • Pharyngo-esophageal constriction: 
    • Caused by the cricoid cartilage
    • Narrowest portion of the esophagus
  • Aortobronchial constriction: caused by proximity to the aortic arch and the left main bronchus (approximately T4)
  • Diaphragmatic constriction: caused by the esophagus passing through the esophageal hiatus of the diaphragm

Microscopic Anatomy

Overview of esophageal wall anatomy

The esophageal wall consists of 4 primary layers: 

  1. Mucosa
  2. Submucosa
  3. Muscularis propria
  4. Adventitia/serosa
Layers of the esophageal wall

Layers of the esophageal wall

Image by Lecturio.

Mucosal layer

Consists of 3 sublayers:

  1. Non-keratinizing stratified squamous epithelium:
    • Lines the lumen
    • Able to resist abrasive forces of food contents and regurgitated stomach acid
    • Z line (also known as the squamocolumnar junction): transition from squamous to columnar epithelium as the esophagus enters the stomach
  2. Lamina propria, a connective tissue layer which contains:
    • Neurovasculature 
    • Lymph tissue
  3. Muscularis mucosae
    • Thin muscular layer
    • Contracts independently of the muscularis externa

Submucosal layer

Located between the mucosal and muscular layers, the submucosal layer is a layer of connective tissue that contains:

  • Larger blood vessels
  • Submucosal (Meissner) nerve plexus (ganglia of the ANS): controls the muscularis mucosa (independent of the muscularis propria)
  • Esophageal glands:
    • Tubuloacinar glands
    • Produce lubricating mucus
  • Longitudinal folds: 
    • Thick folds along the length of the esophagus
    • Allow for distension of the esophagus during swallowing

Muscularis propria

  • Also called the muscularis externa
  • Responsible for the peristaltic waves that move the food toward the stomach
  • Composed of 2 layers:
    • Inner circular muscle fibers
    • Outer longitudinal muscle fibers
  • Consists of both striated and smooth muscles
    • Cranial part (proximal ⅓): striated muscle (under somatic control)
    • Intermediate: mixed
    • Distal part (distal ⅓): smooth muscle (under autonomic control)
  • Contains the myenteric (Auerbach) nerve plexus
    • Ganglia of the ANS that controls the muscularis externa/stimulates peristalsis
    • Located between the 2 layers of smooth muscle

Adventitial/serosal layer

  • Connective tissue surrounding the esophagus
  • Adventia (more fibrous) above the diaphragm
  • Serosa below the diaphragm
  • Contains:
    • Large vessels
    • Lymphatic vessels
    • Nerve fascicles:
      • Vagus nerve
      • Esophageal sympathetic plexus
Low magnification cross-sectional image of the esophagus (H&E stain)

Low-magnification cross-sectional image of the esophagus (H&E stain)

Image by Geoffrey Meyer, PhD

Related videos

Neurovasculature

Arterial supply

  • Cervical part: inferior thyroid artery
  • Thoracic part:
    • Branches of the thoracic aorta:
      • Bronchial branches
      • Esophageal branches
    • Intercostal arteries
  • Abdominal part: 
    • Esophageal branch of the left gastric artery
    • Left phrenic artery
Image displaying some of the arteries responsible for the blood supply of the esophagus

Image displaying some of the arteries responsible for the blood supply of the esophagus

Image: “Thoracic Abdominal Arteries” by OpenStax College. License: CC BY 3.0

Venous drainage

  • Cervical part: inferior thyroid vein
  • Thoracic part: ultimately drains into the inferior vena cava (IVC)
    • Azygos veins
    • Hemiazygos veins
    • Intercostal veins
    • Bronchial veins
  • Abdominal part: ultimately drains into the portal vein via the left gastric vein
  • Clinical relevance:
    • Veins surrounding the esophagus form an important anastomosis between the portal system and the systemic veins.
    • ↑ Pressure in the portal system can lead to esophageal varices, which can cause profuse upper GI bleeding if ruptured

Lymphatic drainage

  • Drained via 2 primary plexuses: dense networks of longitudinal vessels that are continuous with the lymphatic vessels of the pharynx (above) and the gastric mucosa (below)
    • Mucosal plexus
    • Submucosal plexus
  • Cervical part: drains to deep cervical nodes 
  • Thoracic part: drains to posterior mediastinal nodes
  • Abdominal part: drains to left gastric and celiac nodes
  • There is also direct drainage into the thoracic duct.

Innervation

  • Striated muscles in the upper ⅓: recurrent laryngeal nerve (branch of vagus)
  • Smooth muscles: autonomic control via the parasympathetic and sympathetic systems
  • Sympathetic innervation: 
    • Inhibitory: 
      • Causes muscle wall relaxation
      • Tonic contraction of the esophageal sphincters
    • Via postganglionic fibers from stellate and thoracic ganglia
    • Includes afferent visceral pain fibers
  • Parasympathetic innervation:
    • Stimulatory: 
      • Muscle wall contraction/peristalsis waves
      • ↑ Glandular secretions
      • Relaxation of the sphincters to allow passage of food
    • Via branches of the vagus nerve
    • Synapse with ganglia in Meissner and Auerbach plexuses
    • Includes afferent fibers that can detect pressure

Function

The primary function of the esophagus is to transport the partially digested food from the pharynx to the stomach:

  • Wavelike esophageal muscle contractions called peristalsis move food down into the stomach.
  • Mucus production by esophageal glands → lubricate the bolus and help its transportation
  • Tonic contraction of the sphincters → relax when food is swallowed to allow passage downward

Clinical Relevance

  • Esophageal atresia: a congenital anomaly in which the esophagus does not fully develop, creating a blind pouch that prevents swallowed contents from passing into the stomach. Esophageal atresia may cause polyhydramnios in utero (because the fetus is unable to normally swallow the amniotic fluid) and presents at birth with regurgitation of all swallowed contents. The condition is diagnosed by an inability to pass a NB tube into the stomach; the tube will be seen coiling in the blind pouch on chest X-ray. Management is surgical.
  • Tracheoesophageal fistula (TEF): an abnormal communication between the trachea and the esophagus. Tracheoesophageal fistulas are usually associated with other anomalies, especially esophageal atresia, VACTERL association anomalies, and CHARGE syndrome. Presentation will depend on the exact anomaly, but symptoms may include inability to feed, vomiting/regurgitation, excessive secretions, gastric distension from inspired air, and aspiration pneumonia. Management is surgical.
  • Hiatal hernia: protrusion of the abdominal esophagus and/or stomach through the esophageal hiatus. Hiatal hernias may be due to a congenital defect in the diaphragm, trauma, or iatrogenic disease following surgical dissection of the hiatus during certain procedures (e.g., antireflux procedures). Most hiatal hernias are asymptomatic, but larger hernias may cause heartburn, regurgitation, or dysphagia.
  • Esophageal diverticula: outpouchings of the esophageal wall forming small sacs. The outpouchings can be classified according to their location: pharyngoesophageal (Zenker’s diverticulum), midesophageal, or epiphrenic. Symptoms include dysphagia, regurgitation, and halitosis (bad breath).
  • Achalasia: a primary esophageal motility disorder that develops from the degeneration of the myenteric plexus, resulting in impaired lower esophageal sphincter relaxation and absence of normal esophageal peristalsis. Patients typically present with dysphagia to solids and liquids, along with regurgitation. Diagnosis is established by esophageal manometry.
  • Esophagitis: the inflammation or irritation of the esophagus. Esophagitis may be due to medications, infections, acid reflux, eosinophilia, or swallowing corrosive substances. Patients typically present with odynophagia, dysphagia, and retrosternal chest pain. Diagnosis is by endoscopy and biopsy. Treatment for esophagitis depends on the underlying etiology. 
  • Mallory-Weiss syndrome: a condition characterized by a longitudinal tear in the mucosa of the esophagus, usually located at the GE junction. The condition is usually caused by forceful vomiting and is often associated with alcoholism. Mallory-Weiss tears can lead to upper GI bleeding, and patients typically present with epigastric pain and/or hematemesis. Diagnosis and management are via esophageal endoscopy. 
  • Esophageal varices: dilation of esophageal veins that form due to increased pressure in the portal venous system. Esophageal varices are seen in approximately ½ of individuals with cirrhosis. Risk of variceal rupture is high (occurs in approximately ⅓ of patients with varices), and significant, life-threatening hemorrhage can result. Management includes surgical options (e.g., banding the varices, shunt placement) and medical options to reduce portal hypertension (e.g., beta-blockers).
  • Barrett’s esophagus: a precancerous condition in which the normal squamous epithelium of the esophagus is replaced by columnar epithelium due to long-term reflux esophagitis. The condition is associated with an increased risk of esophageal adenocarcinoma. The diagnosis is made by endoscopy, which reveals proximal displacement of the squamocolumnar junction (Z line) away from the GE junction. Treatment is primarily with proton pump inhibitors (PPIs) and lifestyle modifications. 
  • Esophageal cancer: the 2 main types of primary esophageal neoplasms are squamous cell carcinoma ((SCC) typically affecting the upper esophagus) and adenocarcinoma (typically affecting the lower esophagus). Risk factors include smoking, obesity, Barrett’s esophagus, alcohol consumption, and certain dietary factors. Early-stage cancer is often asymptomatic, with dysphagia and weight loss presenting as the disease progresses. Diagnosis is by endoscopic biopsy or image-guided biopsy of the metastatic site.

References

  1. Viswanatha, B. (2015). Esophagus anatomy. Medscape. Retrieved Sep 3, 2021, from https://emedicine.medscape.com/article/1948973-overview#a1 
  2. Mazziotti, M. (2021). Congenital anomalies of esophagus. Medscape. Retrieved Sep 3, 2021, from https://emedicine.medscape.com/article/934420-overview 
  3. Chaudhry, S. (2021). Anatomy, thorax, esophagus. StatPearls. Retrieved Sep 3, 2021, from https://www.statpearls.com/articlelibrary/viewarticle/33963/ 
  4. Saladin, KS, & Miller, L. (Eds.) (2004). The digestive system. In Anatomy and Physiology. (3rd ed., pp. 948–949). 
  5. DeNardi, FG, & Riddell, RH. (1991). The normal esophagus. Am J Surg Pathol, 15(3): 296–309. https://pubmed.ncbi.nlm.nih.gov/1996732/
  6. Nikaki, K, Sawada, A, Ustaoglu, A, & Sifrim, D. (2019). Neuronal control of esophageal peristalsis and its role in esophageal disease. Curr Gastroenterol Rep. 2019, 21(11):59. https://pubmed.ncbi.nlm.nih.gov/31760496/
  7. Sasegbon, A, Hamdy, S. (2017). The anatomy and physiology of normal and abnormal swallowing in oropharyngeal dysphagia. Neurogastroenterol Motil, 29(11). https://pubmed.ncbi.nlm.nih.gov/28547793/

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