The esophagus extends from the lower border of the cricoid cartilage (at the level of the sixth cervical vertebra) to the cardiac orifice of the stomach at the side of the body of the 11th thoracic vertebra. The upper limit in the newborn infant is found at the level of the fourth or fifth cervical vertebra, and it ends higher, at the level of the ninth thoracic vertebra. [2, 3]
In its vertical course, the esophagus has 2 gentle curves in the coronal plane. The first curve begins a little below the commencement of the esophagus and inclines to the left as far as the root of the neck and returns to the midline at the level of fifth thoracic vertebra. 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. [1, 2]
The video below depicts the esophagus as viewed through an esophagoscope in a 3-year-old child.
The videos below depict other views of normal esophageal anatomy via endoscopy.
The video below depicts normal esophageal anatomy via esophagogastroduodenoscopy.
The esophagus has 3 constrictions in its vertical course, as follows:
The first constriction is at 15 cm from the upper incisor teeth, where the esophagus commences at the cricopharyngeal sphincter; this is the narrowest portion of the esophagus and approximately corresponds to the sixth cervical vertebra
The second constriction is at 23 cm from the upper incisor teeth, where it is crossed by the aortic arch and left main bronchus
These measurements are clinically important for endoscopy and endoscopic surgeries of the esophagus.
The esophagus has been subdivided into 3 portions, as follows:
The cervical portion extends from the cricopharyngeus to the suprasternal notch
The thoracic portion extends from the suprasternal notch to the diaphragm
Relationships of the esophagus
The cervical part of the esophagus
The trachea lies anterior to the esophagus and is connected to it by a loose connective tissue. Posteriorly, it is related to prevertebral muscles and prevertebral fascia covering the bodies of sixth, seventh, and eighth cervical vertebra. The thoracic duct lies on the left side at the level of the sixth cervical vertebra. The carotid sheath with its contents and lower poles of the lateral lobes of thyroid gland are in lateral relation to the esophagus on both the sides.
The thoracic part of the esophagus
The esophagus lies between the trachea and vertebral column in the superior mediastinum. On its way down, the esophagus passes behind the aortic arch, and, at the level of T4/T5 intervertebral discs, it enters the posterior mediastinum. The thoracic duct lies on the left side, and the left recurrent laryngeal nerve lies in the left tracheoesophageal groove. Laterally, on the left side, it is related to the aorta and left subclavian artery; on the right side, it is related to the azygos vein.
Anteriorly, the esophagus is related to the trachea, right pulmonary artery, left bronchus, pericardium with left atrium, and diaphragm. Posteriorly, the esophagus is related to the vertebral column, right posterior intercostal arteries, thoracic duct, thoracic part of the aorta, and diaphragm. In the posterior mediastinum, the esophagus is related to the descending thoracic aorta, left mediastinal pleura, azygos vein, and cardiac and pulmonary plexus.
The abdominal part of the esophagus
The esophagus passes through the right crus of the diaphragm. In its abdominal course, it is covered with the peritoneum of the greater sac anteriorly and on its left side, and it is covered with the lesser sac peritoneum on the right side. It comes to lie in the esophageal groove on the posterior surface of the left lobe of the liver and curves sharply to the left to join the stomach at the cardia. The right border continues evenly into the lesser curvature, whereas the left border is separated from the fundus of the stomach by the cardiac notch. 
See the list below:
The cervical portion is supplied by the inferior thyroid artery
The thoracic portion is supplied by bronchial and esophageal branches of the thoracic aorta
The abdominal portion is supplied by ascending branches of the left phrenic and left gastric arteries. 
Venous blood from the esophagus drains into a submucosal plexus. From this plexus, blood drains to the periesophageal venous plexus. Esophageal veins arise from this plexus and drain in a segmental way similar to the arterial supply, as follows:
From the cervical esophagus, veins drain into the inferior thyroid vein
From the thoracic esophagus, veins drain into the azygos veins, hemiazygos, intercostal, and bronchial veins
The esophagus has an extensive, longitudinally continuous, submucosal lymphatic system.  The esophagus has 2 types of lymphatic vessels. A plexus of large vessels is present in the mucous membrane, and it is continuous above with the mucosal lymphatic vessels of pharynx and below with mucosal lymphatic vessels of gastric mucosa. The second plexus of finer vessels is situated in the muscular coat. Efferent vessels from the cervical part drain into the deep cervical nodes. Vessels from the thoracic part drain to the posterior mediastinal nodes and from the abdominal part drain to the left gastric nodes. Some vessels may pass directly to the thoracic duct. [1, 2]
Lymphatic drainage of the esophagus contains little barrier to spread, and esophageal lymphatics are densely interconnected. Hence, esophagus carcinoma can spread through the length of the esophagus via lymphatics and may have nodal involvement several centimeters away from the primary lesion. 
Recurrent laryngeal branches of the vagus nerve supply the striated muscle in the upper third of the esophagus, and cell bodies for these fibers are situated in the rostral part of the nucleus ambiguus. Motor supply to the nonstriated muscle is parasympathetic, and cell bodies for these fibers are situated in the dorsal nucleus of vagus. These fibers reach the esophagus through the vagus and its recurrent laryngeal branches. They synapse in the esophagus wall in the ganglia of submucosal plexus (Meissner) and myenteric plexus (Auerbach). The myenteric is situated between the outer longitudinal and inner circular muscle fibers. From these plexuses, short, postganglionic fibers emerge to innervate the mucous glands and smooth muscle fibers within the walls of the esophagus. 
Vasomotor sympathetic fibers that supply the esophagus arise from the upper 4-6 thoracic spinal cord segments. Fibers from the upper ganglia pass to the middle and inferior cervical ganglia and synapse on postganglionic neurons. The axons of these neurons innervate the vessels of the cervical and upper thoracic esophagus. Postsynaptic fibers from the lower ganglia pass to the esophageal plexus to innervate the distal esophagus. Afferent visceral pain fibers travel via the sympathetic fibers to the first 4 segments of the thoracic spinal cord. 
The image below depicts the esophageal musculature.
Histologically, the esophagus has the following 4 concentric layers (see the image below)  :
Adventitial layerMicrograph showing 4 layers of the esophagus.
Mucosa forms the innermost layer and is formed by a nonkeratinizing stratified squamous epithelium that is continuous with that of the pharynx. Mucosal epithelium changes from squamous cell epithelium to columnar cell epithelium at the gastroesophageal junction. This junction has been termed the "Z line" (see videos below) or squamocolumnar junction. [2, 3]
The second layer is formed by submucosa, and it loosely connects the mucous membrane and the muscular coat. This layer contains the larger blood vessels, the submucosal (Meissner) nerve plexus, and esophageal glands (see the following image). [2, 3]
The third layer is formed by circular and longitudinal muscle fibers. The longitudinal layer is generally thicker than the circular layer; both are described as follows (see the image below):
Inner circular muscle fibers: These fibers are continuous superiorly with the fibers of the cricopharyngeal part of the inferior constrictor and inferiorly with oblique fibers of the stomach. 
Outer longitudinal muscle fibers: The longitudinal muscle fibers form a continuous coat around the whole of the esophagus except posterosuperiorly, 3-4 cm below the cricoid cartilage; here, they diverge as 2 fascicles that ascend obliquely to the anterior aspect of the esophagus [1, 2]Micrograph showing circular and longitudinal muscle fibers.
The proximal one-third of the esophagus consists primarily of striated muscle. Smooth muscle predominates in the distal portion. 
The fourth and the outermost fibrous layer is formed by external adventitia of irregular, dense connective tissue containing many elastic fibers.
The esophagus has no serosa, which makes it unique to the rest of the gastrointestinal tract. 
The most common congenital anomalies of the esophagus are esophageal atresia and tracheoesophageal fistula. The cause of esophageal atresia is thought to be a failure of the esophageal endoderm to proliferate rapidly during the fifth week to keep up with the elongation of the embryo. The cause for tracheoesophageal fistula and why the 2 defects are usually found together is related to the fact that the respiratory diverticulum buds anteriorly from the cranial foregut and is therefore intimately related to esophageal development. 
Congenital esophageal mucosal webs or muscular hypertrophy can cause symptomatic narrowing of the esophagus. Esophageal duplication can take many forms and may manifest as a neck mass or dysphagia. Dysphagia lusoria is induced by vascular anomalies involving the aortic root. 
See also Congenital Anomalies of the Esophagus.