Esophagus - anatomy and development
Braden Kuo, M.D.andDaniela Urma, M.D.About the contributors
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Key Points
The adult human esophagus is an 18- come 25-cm long muscular tube that has cervical, thoracic, and ab parts.You are watching: What transition in epithelial type exists at the gastroesophageal junction
The esophagus wall surface is created of striated muscle in the upper part, smooth muscle in the reduced part, and a mixture the the 2 in the middle.The myenteric plexus is well arisen in the smooth muscle, however is additionally present in the striated muscle part of the esophagus.The function of the myenteric plexus in the striated stomach is no well understood.Esophagus creates from foregut and also by mainly 10 is lined by ciliated epithelial cells.Beginning at 4 months, the ciliated epithelium starts come be replaced by squamous epithelium. In ~ either finish of the stomach the ciliated epithelium offers rise come esophageal glands.The upper esophagus is acquired from branchial arches 4, 5, and 6, but the source of the reduced esophagus is not known.The advance of various elements of esophageal wall requires coordination of a range of genes and also mediators.Esophageal peristalsis appears in the first trimester, and also gastroesophageal reflux can be documented in the second trimester.
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Introduction
From mouth come stomach, the food conduit is composed of the dental cavity, pharynx, and also esophagus. The stomach serves as a dynamic tube, pushing food towards the stomach, where digestion and absorption have the right to take place. Mucus produced by the esophageal mucosa gives lubrication and also eases the passage of food. Energetic peristaltic contractions propel residual product from the esophagus right into the stomach. Throughout vomiting and reflux, the esophagus likewise serves as a passageway because that gastrointestinal (GI) materials traveling retrograde native the stomach or little intestine.
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Embryology
The an initial stages that life are separated into the embryonic and also fetal periods. The embryonic duration extends from fertilization to week 9. The fetal duration lasts native the finish of the main 9 come birth. From days 0 to 14, the human embryo creates into a bilaminar disc of ectoderm and also endoderm, through the endoderm developing the lining the the yolk sac. The endoderm is the scaffold for the future cradle tract. The ectoderm gives rise come epidermis and also neural plates. With the neurulation process, the neural plates evolve come neural tube and also neural crest cells. The neural pipe is the precursor for the spinal cord and brain. The neural stakes cells, placed in between the dorsal neural tube and also the overlying epidermis, move out to type the peripheral nervous system by week 4. On job 15, the third embryonic layer, the mesoderm, appears and also provides the substrate for the connective tissue, angioblasts, smooth muscle, and serosal layers of the gut. By work 21, the mesoderm is thickened and also forms longitudinal masses dubbed the paraxial mesoderm. By job 28, the paraxial mesoderm fragments progressively indigenous cranial come caudal right into cubes the tissue referred to as somites. This process ends through the development of 33 to 35 somites by day 31 of embryo development.1
Mesoderm proliferation and segmentation, which takes place in between the endoderm and also ectoderm, induces countless transformations in the endoderm.2 at the very same time, the human embryo elongates craniocaudally and folds laterally. The dorsal part of the yolk sac, written of endoderm, is compressed through the lateral folding of the embryo and is incorporated as a rim throughout the fourth week. Hence the human being embryo becomes a "body cylinder" splitting the yolk sac into intraembryonic and also extraembryonic parts.3 The intraembryonic part is the beginning of cradle tube and also its accessory glands. The extraembryonic component regresses and disappears roughly week 12. In ~ this point, the early on digestive system divides right into foregut, midgut, and also hindgut.
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Gut development takes place in four major patterned axes: anterior-posterior, dorsal-ventral, left-right, and also craniocaudal. Every axis breakthrough is based on the epithelial-mesenchymal interaction mediated by particular molecular pathways.4 Thus, growth determinants such as Wnt5a (expressed by mesoderm), endodermal proteins Six2/Sox2, as well as Hoxa-2, Hoxa-3, and also Hoxb-4 regulate esophageal breakthrough in the anterior-posterior axis.5 this factors influence both the esophageal environment and also the neural crest cell by making the environment much more permissive for neural crest cells and by prepare the neural crest cells to move within the esophagus4, 5 (Figure 1).
The LES is innervated by both parasympathetic (vagus) and sympathetic (primarily splanchnic) nerves, through the vagal pathways being necessary for reflex be safe of LES.42 Vagal sensory afferents from the LES and distal esophagus end in cell core tractus solitarius that the hindbrain. The engine innervation of the LES is topographically noted through preganglionic fibers from the dorsal motor nucleus that the vagus. The dorsal engine nucleus and also the tractus solitarius nucleus form a dorsal vagal complex in the hindbrain that collaborates reflex regulate of the sphincter.42