Squamous cell carcinoma used to be the most common type of esophageal cancer in the United States. Cancers that start in gland cells cells that make mucus are called adenocarcinomas. Adenocarcinomas are often found in the lower third of the esophagus lower thoracic esophagus.
In some conditions, such as Barrett's esophagus , gland cells begin to replace the squamous cells in the lower part of the esophagus, and this might lead to adenocarcinoma.
Adenocarcinomas that start at the area where the esophagus joins the stomach the GE junction, which includes about the first 2 inches 5 cm of the stomach , tend to behave like cancers in the esophagus and are treated like them, as well. Venous drainage of abdominal portions empties primarily into left gastric veins. Other veins that drain esophageal venous plexus are short gastric veins, splenic vein, left gastroepiploic vein, and branches of an inferior phrenic vein.
Lower esophageal veins connect to superior caval venous system by azygos and hemiazygos veins with multiple shunts, and other multiple shunts are located between inferior caval system and lower esophagus Figure 7. Retrograde flow of esophageal venous system causes venous dilatation and varices, and these varices can cause fatal bleeding [ 2 , 14 , 17 ].
Anti-reflux mechanism of esophagus. Lymphatics are located in every layer of esophagus, but primarily at lamina propria, forming a giant network system. Cervical lymphatics empty internal jugular lymph nodes and upper tracheal lymph nodes.
An internal jugular lymphatic system that forms deeper cervical lymphatic system connects with lymphatic duct at right side and thoracic duct at left side. Lymphatics of thoracic esophagus empty posterior parietal, diaphragmatic, tracheal, tracheobronchial, retrocardiac, and infracardiac lymph nodes.
Abdominal parts of lymphatic system empty left gastric, paracardiac lymph nodes, and all these nodes connect to coeliac lymph nodes. Coeliac lymph nodes empty cisterna chyli or thoracic duct. Posterior parietal lymph nodes include posterior mediastinal and intercostal lymph nodes and connect with thoracic duct or right lymphatic duct.
Only posterior part of diaphragmatic lymph nodes are connected to esophageal lymphatic system, and these lymph nodes empty to posterior parietal lymph nodes.
Tracheal or paratracheal lymph nodes are located on two sides of trachea, and tracheobronchial lymph nodes are located around bifurcation of trachea. Tuberculosis, which causes necrosis and fibrosis of tracheobronchial lymph nodes, forms traction diverticula of esophagus. These two lymphatic systems form a broch mediastinal lymphatic chain that empties to thoracic duct or right lymphatic duct Figure 8 [ 18 , 19 ].
Lymphatics of esophagus. Parasympathetic and sympathetic nerves form esophageal innervation, carrying stimuli to esophageal muscles, glands, veins, and arteries.
Parasympathatic fibers that innervate pharynx and upper part of esophagus come from ambiguous nuclei of brain. Esophageal innervation is primarily accomplished by vagus nerves, which end at dorsal vagal nuclei of brain. Cervical esophagus takes thin fibers from both recurrent laryngeal nerves. Both left and right recurrent laryngeal nerves arise from vagus nerves, but on left side, a recurrent laryngeal nerve is closer to aortic arch.
On right side, it is closer to subclavian artery. Finally, left and right recurrent laryngeal nerves run in sulcus between trachea and esophagus. The thoracic esophagus is primarily innervated by vagus nerves, but the upper part of thoracic esophagus takes some fibers from left recurrent laryngeal nerve.
Vagus nerve fibers form two to four branches under tracheal bifurcation, and these nerve branches are located on anterior face of esophagus at level of posterior mediastinum. Near esophageal hiatus, these nerve branches unite and form two vagal trunks of esophagus. Variation of vagal trunks is important during vagotomy. A surgeon should be aware of these variations and be careful because more than one branch can be found in anterior or posterior vagal trunk or both.
The upper part of esophagus is innervated by pharyngeal plexus, which is fed by upper cervical ganglions, middle cervical ganglions, and sympathetic trunks of vertebral ganglions while running downward. Superior parts of the thoracic esophagus are innervated by stellate ganglion and subclavian ansa. Lower parts of thoracic esophagus are innervated by greater splanchnic nerves that end at coeliac plexus.
Left greater splanchnic nerve and right inferior phrenic nerve innervate abdominal esophagus [ 20 , 21 ]. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications.
Edited by Jianyuan Chai. We are IntechOpen, the world's leading publisher of Open Access books. Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Abstract Anatomy knowledge is the basic stone of healing diseases. Keywords anatomy esophagus parts of esophagus blood supply of esophagus innervation of esophagus. Introduction Esophagus is a muscular tube-like organ that originates from endodermal primitive gut, 25—28 cm long, approximately 2 cm in diameter, located between lower border of laryngeal part of pharynx Figure 1 and cardia of stomach.
Mucosa Nonkeratinized stratified squamous epithelium covers all esophageal lumen. Submucosa This layer consists of elastic and collagen fibers that form a dense, irregular connective tissue. Muscularis propia Both longitudinal and circular muscles form tube-like esophagus: longitudinal muscle fibers are located superficially and the circular muscle fibers are located deeply. Adventitia This layer surrounds most of the esophagus and consists of loose connective tissue. Cervical esophagus Cervical esophagus starts at inferior margin of cricoid cartilage that corresponds to corpus of 6th cervical vertebra.
Surrounding structures Esophagus runs in deepest fascial plane of neck, leaning between trachea anteriorly and vertebra posteriorly.
Importance of surrounding structures Sagittal septa, which forms retropharyngeal and retro-esophagial spaces, blocks the diffusion of abscess of this area to upper mediastinum, but abscess can diffuse via pretracheal space to the upper mediastinum and can cause a fatal complication. Thoracic esophagus Measuring 16—18 cm in length, thoracic esophagus is in upper and posterior mediastinum.
Surrounding structures Most important and challenging structure in this region is thoracic duct, which lies behind esophagus throughout thorax. Importance of surrounding structures Close proximity of upper two-thirds of esophagus to thoracic duct increases risk of thoracic duct injury in middle and upper mediastinal dissection of esophagus; thus, careful dissection should be performed in this area. Abdominal esophagus Abdominal esophagus is 1—2. Surrounding structures Following structures are located near abdominal esophagus: posterior side segment of two-thirds of liver, left vagus nerve and esophageal plexus anteriorly, left and right crus of diaphragm, aorta and left inferior phrenic artery posteriorly, caudate lobe of liver at the right side, and fundus of stomach at left side.
Arteries of esophagus Inferior thyroid artery provides primary arterial flow to the cervical esophagus, and subclavian artery, main carotid artery, vertebral arteries, ascendant pharyngeal artery, superficial cervical artery, and costocervical trunk are other arterial blood flow providers to cervical esophagus. Veins of esophagus Venous system of esophagus begins at submucosal plexus, which perforates muscular layer and empties into azygos system.
Lymphatics of esophagus Lymphatics are located in every layer of esophagus, but primarily at lamina propria, forming a giant network system.
Innervation of esophagus: Parasympathetic and sympathetic nerves form esophageal innervation, carrying stimuli to esophageal muscles, glands, veins, and arteries. Parasymphatic innervation Parasympathatic fibers that innervate pharynx and upper part of esophagus come from ambiguous nuclei of brain.
Braden Kuo, M. About the contributors. From mouth to stomach, the food conduit consists of the oral cavity, pharynx, and esophagus. The esophagus serves as a dynamic tube, pushing food toward the stomach, where digestion and absorption can take place. Mucus produced by the esophageal mucosa provides lubrication and eases the passage of food. Active peristaltic contractions propel residual material from the esophagus into the stomach.
During vomiting and reflux, the esophagus also serves as a passageway for gastrointestinal GI contents traveling retrograde from the stomach or small intestine. The first stages of life are divided into the embryonic and fetal periods. The embryonic period extends from fertilization to week 9. The fetal period lasts from the end of the week 9 to birth. From days 0 to 14, the human embryo develops into a bilaminar disk of ectoderm and endoderm, with the endoderm forming the lining of the yolk sac.
The endoderm is the scaffold for the future digestive tract. The ectoderm gives rise to epidermis and neural plates. Through the neurulation process, the neural plates evolve to neural tube and neural crest cells. The neural tube is the precursor for the spinal cord and brain. The neural crest cells, placed between the dorsal neural tube and the overlying epidermis, migrate out to form the peripheral nervous system by week 4.
On day 15, the third embryonic layer, the mesoderm, appears and provides the substrate for the connective tissue, angioblasts, smooth muscle, and serosal layers of the gut. By day 21, the mesoderm is thickened and forms longitudinal masses called the paraxial mesoderm. By day 28, the paraxial mesoderm fragments progressively from cranial to caudal into cubes of tissue called somites. This process ends with the formation of 33 to 35 somites by day 31 of embryo development. Mesoderm proliferation and segmentation, which takes place between the endoderm and ectoderm, induces numerous transformations in the endoderm.
The dorsal part of the yolk sac, composed of endoderm, is compressed by the lateral folding of the embryo and is incorporated as a rim during the fourth week. Thus the human embryo becomes a "body cylinder" dividing the yolk sac into intraembryonic and extraembryonic parts.
The extraembryonic part regresses and disappears around week At this point, the early digestive system divides into foregut, midgut, and hindgut.
Gut development takes place in four major patterned axes: anterior-posterior, dorsal-ventral, left-right, and craniocaudal. Each axis development is based on the epithelial-mesenchymal interactions mediated by specific molecular pathways. The primordial gut is a long tube extending the length of the embryo.
Its blood vessels are derived from the vessels that supplied the yolk sac. The Developing Human, 7th ed. Philadelphia: Elsevier, Inc. During week 4, the foregut develops a small diverticulum on its ventral surface adjacent to the pharyngeal gut. This tracheobronchial diverticulum subsequently elongates and separates gradually from the dorsal foregut through the formation of the esophagotracheal septum to become the primitive respiratory tract.
The remaining part of the foregut rapidly elongates with the craniocaudal growth of the embryonic body. In the seventh and eighth weeks, the luminal epithelium proliferates and almost completely occludes the foregut with only residual channels persisting. Unlike other species, complete occlusion of the foregut has not been observed in human embryos. During the fourth month, a stratified squamous epithelium begins to replace the ciliated epithelium, a process that continues until birth.
Residual islands of ciliated epithelium at the proximal and distal ends of the esophagus remain and give rise to esophageal glands. During week 6 of gestation, the circular muscle coat and ganglion cells of the myenteric plexus form.
During week 7, blood vessels enter the submucosa. The smooth muscle of the lower esophagus and the lower esophageal sphincter LES are derived from the mesenchyme of the somites surrounding the foregut. The striated muscle forming the muscularis propria of the upper part of the esophagus and the upper esophageal sphincter is derived from mesenchyme of the branchial arches 4, 5, and 6.
This origin explains the upper esophageal sphincter innervation by the vagal nerve the branchial arch 5 nerve and by the recurrent laryngeal nerve a branch of the vagus nerve, the branchial arch 6 nerve. The embryologic origin of the gastroesophageal junction is still controversial, but gastric rotation together with augmentation of the fundus of the stomach are believed to determine its formation.
The middle third of esophagus consists of a mixture of smooth and skeletal muscle. The origin of this mixture is controversial, with somites and endoderm influencing each other by molecular mechanisms.
When definitive endoderm was co-cultured with somitic mesoderm, it stimulated more smooth muscle development than skeletal muscle from the mesenchymal somitic cells. The smooth muscle differentiation begins after the neural crest cells colonize the gut and maturates on the rostrocaudal axis.
At the beginning of week 4, the neural crest cells enter the foregut and migrate rostrocaudally to reach the terminal hindgut by week 7 and give rise to the myenteric plexus. Interstitial cells of Cajal ICC emerge from gut mesenchyme around week 9. By week 14, the ICC s form a network surrounding the myenteric plexus. The ICC s form after the differentiation of smooth muscle layers. Whether ICC differentiation requires neural crest cells has not been clearly established yet, and some recent studies identified ICC in the absence of neural crest cells.
The development of concentric layers of smooth muscle, ICC s, and neural crest cells as precursors of the enteric nervous system is a coordinated process, controlled by numerous genes and signaling molecules including transcription factors e.
The myenteric plexus has cholinesterase activity by week 9. Several investigators have suggested that the esophagus is capable of peristalsis in the first trimester.
The pressure at the LES approaches that of the adult at 3 to 6 weeks of age. The esophagus is a flattened muscular tube of 18 to 26 cm from the upper sphincter to the lower sphincter. Between swallows the esophagus is collapsed but the lumen can distend to approximately 2 cm in the anterior-posterior dimension and up to 3 cm laterally to accommodate a swallowed bolus. The esophagus connects the pharynx to the stomach.
Beginning in the neck, at the pharyngoesophageal junction C vertebral interspace at the inferior border of the cricoid cartilage , the esophagus descends anteriorly to the vertebral column through the superior and posterior mediastinum. After traversing the diaphragm at the diaphragmatic hiatus T10 vertebral level the esophagus extends through the gastroesophageal junction to end at the orifice of the cardia of the stomach T11 vertebral level.
Topographically, there are three distinct regions: cervical, thoracic, and abdominal. The cervical esophagus extends from the pharyngoesophageal junction to the suprasternal notch and is about 4 to 5 cm long.
At this level, the esophagus is bordered anteriorly by the trachea, posteriorly by the vertebral column, and laterally by the carotid sheaths and the thyroid gland. The thoracic esophagus extends from the suprasternal notch to the diaphragmatic hiatus, passing posterior to the trachea, the tracheal bifurcation, and the left main stem bronchus. The esophagus lies posterior and to the right of the aortic arch at the T4 vertebral level.
From the level of T8 until the diaphragmatic hiatus the esophagus lies anteriorly to the aorta. The abdominal esophagus extends from the diaphragmatic hiatus to the orifice of the cardia of the stomach. Forming a truncated cone, about 1 cm long, the base of the esophagus transitions smoothly into the cardiac orifice of the stomach.
The abdominal esophagus lies in the esophageal groove on the posterior surface of the left lobe of the liver. Two high-pressure zones prevent the backflow of food: the upper and lower esophageal sphincter.
These functional zones are located at the upper and lower ends of the esophagus but there is not a clear anatomic demarcation of the limits of the sphincters. Structurally, the esophageal wall is composed of four layers: innermost mucosa, submucosa, muscularis propria, and adventitia. Unlike the remainder of the GI tract, the esophagus has no serosa. On endoscopy, the esophageal lumen appears as a smooth, pale pink tube with visible submucosal blood vessels. The transition from esophageal to gastric mucosa is known as the Z-line and consists of an irregular circumferential line between two areas of different colored mucosa.
The gastric mucosa is darker than the pale pink esophageal mucosa. Peristaltic waves can be seen during endoscopic examination. The rich arterial supply of the esophagus is segmental Figure 2. The branches of the inferior thyroid artery provide arterial blood supply to the upper esophageal sphincter and cervical esophagus.
The paired aortic esophageal arteries or terminal branches of bronchial arteries supply the thoracic esophagus. The left gastric artery and a branch of the left phrenic artery supply the LES and the most distal segment of the esophagus. The arteries supplying the esophagus end in an extensive, dense network in the submucosa.
The copious blood supply and network of potentially anastomotic vessels may explain the rarity of the esophageal infarction.
Source: Netter medical illustration with permission from Elsevier. All rights reserved. The venous supply is also segmental. Figure 3. From the dense submucosal plexus the venous blood drains into the superior vena cava. The veins of the proximal and distal esophagus drain into the azygous system. Collaterals of the left gastric vein, a branch of the portal vein, receive venous drainage from the mid-esophagus.
The submucosal connections between the portal and systemic venous systems in the distal esophagus form esophageal varices in portal hypertension. These submucosal varices are sources of major GI hemorrhage in conditions such as cirrhosis.
The esophagus, like the rest of the viscera, receives dual sensory innervation, traditionally referred to as parasympathetic and sympathetic, but more properly based on the actual nerves, vagal, and spinal 21 Figure 4. The spinal afferents have their cell bodies in the dorsal root ganglia and terminate in the spinal column and in the nucleus gracilis and cuneatus in the brainstem. From there, they project, through the thalamus, to primary sensory and insular cortical areas.
The motor innervation of the esophagus is predominantly via the vagus nerve. The cell bodies of the vagal efferent fibers innervating the upper esophageal sphincter and the proximal striated muscle esophagus arise in the nucleus ambiguus, whereas fibers destined for the distal smooth-muscle segment and the LES originate in the dorsal motor nucleus of the vagus nerve. The esophagus receives parasympathetic and sympathetic innervation that regulates glandular secretion, blood vessel caliber, and the activity of striated and smooth muscle.
The parasympathetic nerve supply comes from the nucleus ambiguus and dorsal motor nucleus of the vagus nerve and provides motor innervation to the esophageal muscular coat and secretomotor innervation to the glands. The sympathetic nerve supply comes from the cervical and the thoracic sympathetic chain spinal segments T1—T10 and regulates blood vessel constriction, esophageal sphincters contractions, relaxation of the muscular wall, and increases in glandular and peristaltic activity.
The thin nerve fibers and numerous ganglia of the intramural myenteric and the submucosal plexi provide the intrinsic innervation of the esophagus. The ganglia that lie between the longitudinal and the circular layers of the tunica muscularis form the myenteric or Auerbach's plexus, whereas those that lie in the submucosa form the submucous or Meissner's plexus.
Auerbach's plexus regulates contraction of the outer muscle layers, whereas Meissner's plexus regulates secretion and the peristaltic contractions of the muscularis mucosae. A network of fibers interconnects these two plexi. In the striated muscle the role of the neurons of the myenteric plexus is largely unknown. Positron emission tomography PET and functional magnetic resonance imaging fMRI have been used to map the central nervous system projections from the esophagus.
Esophageal stimulation at the subliminal and liminal levels is sensed peripherally and transmitted to the brain for further processing and modulation. Esophageal sensory innervation is carried by the vagus nerve to the nodose ganglion and projects through the brainstem, through the thalamus, to terminate in the cortex. Lymphatic drainage in the esophagus consists of two systems: the lymph channels and lymph nodules. Figure 5. The lymph channels begin in the esophageal tissue space as a network of endothelial channels 20—30 m or as blind endothelial sacculations 40—60 m.
Some authors propose that precapillary spaces exist in the lamina mucosa, but others contend that there is an absence of true lymphatic capillaries in the upper and middle levels of the lamina mucosa. Lymph capillaries drain into collecting lymph channels — m that continue through the esophageal muscular coat and are distributed parallel to the long axis of the esophagus. Paired semilunar valves within the collecting channels determine the direction of flow.
The collecting lymph channels merge into small trunks that open into the regional lymph nodes. As with esophageal innervation, the lymphatic drainage of the esophagus differs in the striated and smooth muscle regions. The lymphatics from the proximal third of the esophagus drain into the deep cervical lymph nodes, and subsequently into the thoracic duct.
The lymphatics from the middle third of esophagus drain into the superior and posterior mediastinal nodes. Lymphatics of the distal third of the esophageal follow the left gastric artery to the gastric and celiac lymph nodes.
There are considerable interconnections among these three drainage regions primarily owing to the dual embryologic origin of lymphatic pathways from branchiogenic and body mesenchyme.
The muscular coat consists of an external layer of longitudinal fibers and an internal layer of circular fibers Figure 6. The longitudinal fibers are arranged proximally in three fasciculi. The ventral fasciculus is attached to the vertical ridge on the posterior surface of the lamina of the cricoid cartilage by the tendocricoesophageus. The two lateral fasciculi are continuous with the muscular fibers of the pharynx. The longitudinal fibers descend in the esophagus and combine to form a uniform layer that covers the outer surface of the esophagus.
The circular muscle layer provides the sequential peristaltic contraction that propels food toward the stomach. The circular fibers are continuous with the inferior constrictor muscle of the hypopharynx; they run transverse at the cranial and caudal regions of the esophagus, but oblique in the body of the esophagus.
The internal muscular layer is thicker than the external muscular layer. Below the diaphragm, the internal circular muscle layer thickens and the fibers become semicircular and interconnected, constituting the intrinsic component of the LES.
Accessory bands of muscle connect the esophagus and the left pleura to the root of the left bronchus and the posterior of the pericardium. 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.
The upper esophageal sphincter UES is a high-pressure zone situated between the pharynx and the cervical esophagus Figure 7. The UES is a musculocartilaginous structure composed of the posterior surface of the thyroid and cricoid cartilage, the hyoid bone, and three muscles: cricopharyngeus, thyropharyngeus, and cranial cervical esophagus.
Each muscle plays a different role in UES function. The thyropharyngeus muscle is obliquely oriented, whereas the cricopharyngeus muscle is transversely oriented. Between these two muscles, there is a zone of sparse musculature—the Killian's triangle, from which Zenker's diverticulum might emerge.
The cricopharyngeus CP muscle is a striated muscle attached to the cricoid cartilage. It forms a C-shaped muscular band that produces maximum tension in the anteroposterior direction and less tension in lateral direction.
It is composed of a mixture of fast- and slow-twitch fibers, with the slow fibers being predominant and having a diameter of 25 to 35 m. The CP is suspended between the cricoid processes, surrounds the narrowest part of pharynx, and extends caudally where it blends with the circular muscle of the cervical esophagus.
The cervical esophagus contains predominantly striated muscle fibers, but occasionally smooth fibers are found in the center of the muscle. The external longitudinal layer of the cervical esophagus originates from the dorsal plane of the cricoid cartilage constituting a sparse muscle area: the Laimer's triangle.
The external longitudinal layer courses down the length of the entire esophagus. At its distal end the longitudinal fibers become more oblique and end along the anterior and posterior gastric wall.
Upper esophageal sphincter function is controlled by a variety of reflexes that involve afferent inputs to the motor neurons innervating the sphincter. These reflexes elicit either contraction or relaxation of the tonic activity of the UES. Inability of the sphincter to open or discoordination of timing between the opening of the UES with the pharyngeal push of ingested contents leads to difficulty in swallowing known as oropharyngeal dysphagia.
The lower esophageal sphincter is a high-pressure zone located where the esophagus merges with the stomach Figure 8. The LES is a functional unit composed of an intrinsic and an extrinsic component. The intrinsic structure of LES consists of esophageal muscle fibers and is under neurohormonal influence. The extrinsic component consists of the diaphragm muscle, which functions as an adjunctive external sphincter that raises the pressure in the terminal esophagus related to the movements of respiration.
Figure 9. Malfunction in any of these two components is the cause of gastroesophageal reflux and its subsequent symptoms and mucosal changes. The esophageal opening is created by a loop of right crux of the diaphragm.
The intrinsic component of the LES is composed of circular layers of the esophagus, clasp-like semicircular smooth muscle fibers on the right side, and sling-like oblique gastric muscle fibers on the left side. The clasp-like semicircular fibers have significant myogenic tone but are not very responsive to cholinergic stimulation, whereas the sling-like oblique gastric fibers have little resting tone but contract vigorously to cholinergic stimulation. The extrinsic component of the LES is composed of the crural diaphragm, which forms the esophageal hiatus, and represents a channel through which the esophagus enters into the abdomen.
The crural diaphragm encircles the proximal 2 to 4 cm of the LES , and determines inspiratory spike-like increases in LES pressure as measured by esophageal manometry. The endoscopic localization of the LES is different from the manometric localization. The endoscopic localization of the LES is presumably determined by changes in the esophageal mucosa color owing to transition from nonstratified squamous esophageal epithelium to the gastric mucosa, changes known as the Z-line.
Three-dimensional 3D manometric measures of the lower esophageal high-pressure zone showed a marked radial and longitudinal asymmetry, with higher pressures toward the left posterior direction. Radial pressures peak at the respiratory inversion point during esophageal manometry where inspiration converts from a positive pressure as measured by pressure sensors to a negative pressure as the pressure sensor enters the intrathoracic cavity.
The high-pressure zone appears to coincide with asymmetric thickening of the muscular layer at the gastroesophageal junction, which corresponds to the gastric "sling" fibers and to the semicircular "clasp" fibers.
The LES is innervated by both parasympathetic vagus and sympathetic primarily splanchnic nerves, with the vagal pathways being essential for reflex relaxation of LES.
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