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1 the Anatomy and Physiology of the Oesophagus

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1 the Anatomy and Physiology of the Oesophagus 111 2 3 1 4 5 6 The Anatomy and Physiology of 7 8 the Oesophagus 9 1011 Peter J. Lamb and S. Michael Griffin 1 2 3 4 5 6 7 8 911 2011 location deep within the thorax and abdomen, 1 Aims a close anatomical relationship to major struc- 2 tures throughout its course and a marginal 3 ● To develop an understanding of the blood supply, the surgical exposure, resection 4 surgical anatomy of the oesophagus. and reconstruction of the oesophagus are 5 ● To establish the normal physiology and complex. Despite advances in perioperative 6 control of swallowing. care, oesophagectomy is still associated with the 7 highest mortality of any routinely performed ● To determine the structure and function 8 elective surgical procedure [1]. of the antireflux barrier. 9 In order to understand the pathophysiol- 3011 ● To evaluate the effect of surgery on the ogy of oesophageal disease and the rationale 1 function of the oesophagus. for its medical and surgical management a 2 basic knowledge of oesophageal anatomy and 3 physiology is essential. The embryological 4 Introduction development of the oesophagus, its anatomical 5 structure and relationships, the physiology of 6 The oesophagus is a muscular tube connecting its major functions and the effect that surgery 7 the pharynx to the stomach and measuring has on them will all be considered in this 8 25–30 cm in the adult. Its primary function is as chapter. 9 a conduit for the passage of swallowed food and 4011 fluid, which it propels by antegrade peristaltic 1 contraction. It also serves to prevent the reflux Embryology 2 of gastric contents whilst allowing regurgita- 3 tion, vomiting and belching to take place. It is The embryonic development of the oesophagus 4 aided in these functions by the upper and lower like that of all major organ systems takes place 5 oesophageal sphincters sited at its proximal and between the fourth and eighth weeks of gesta- 6 distal ends. Any impairment of oesophageal tion as the three germ layers differentiate 7 function can lead to the debilitating symptoms into specific tissues. During the fourth week, as 8 of dysphagia, gastro-oesophageal reflux or the embryo folds, part of the dorsal yolk sac is 9 oesophageal pain. incorporated into the developing head as the 5011 The apparently simple basic structure of foregut (Figure 1.1a). This ultimately develops 1 the oesophagus belies both its physiological into not only the oesophagus, stomach and duo- 2 importance and the dangers associated with denum but also the pharynx, lower respiratory 311 surgical intervention. As a consequence of its system, liver, pancreas and biliary tree. 1 2 1 · UPPER GASTROINTESTINAL SURGERY Early in the fourth week the laryngotracheal tracheo-oesophageal fistula, which is commonly 1111 diverticulum develops in the midline of the associated with oesophageal atresia. Complete 2 ventral wall of the foregut. This extends caudally failure to close the tracheo-oesophageal septum 3 and becomes separated from the foregut by is much less common and results in a laryngo- 4 growth of the tracheo-oesophageal folds, which oesophageal cleft. Normally the oesophagus 5 fuse to form the tracheo-oesophageal septum lengthens rapidly as a result of cranial body 6 (Figure 1.1b and c). This creates the laryngotra- growth (with descent of the heart and lungs) to 7 cheal tube (ultimately the larynx, trachea, reach its final relative length by the seventh 8 bronchi and lungs) and dorsally the oesophagus week. During elongation the lumen is tem- 9 [2]. Failure of this separation can occur due to porarily obliterated by proliferation of endo- 1011 a shortage of proliferating endothelial cells in dermal cells and failure to recanalise results in 1 the tracheo-oesophageal folds. This results in a oesophageal atresia. 2 Oesophageal atresia is present in approxi- 3 mately 1 in 3000 live births. In 85% of cases 4 a Aorta there is proximal oesophageal atresia with a 5 Coeliac axis Midgut fistula between the distal oesophagus and the 6 Hindgut respiratory tract, usually the trachea. Less 7 common combinations are oesophageal atresia 8 without a fistula (10%), a fistula without atresia 9 (2%) and a fistula between the upper oesopha- 2011 gus and trachea (1%). Because of the embryonic 1 time period during which these failures take 2 place 50% of oesophageal malformations are 3 associated with major defects in other organ 4 Brain systems. In 25% these are cardiovascular, 5 Heart most commonly a patent ductus arteriosus, 6 Foregut although musculoskeletal and other gastroin- 7 Laryngotracheal diverticulum testinal defects, classically an imperforate anus, 8 are also seen. 9 The artery of the foregut is the coeliac axis 3011 (i) (ii) and whilst this supplies the distal oesophagus, 1 Pharynx more proximally it takes branches directly from 2 Oesophagus the developing aorta. During the developmental 3 b sequence described, the epithelium and glands 4 of the oesophagus are derived from endoderm. 5 The striated skeletal muscle of the proximal 6 third of the oesophagus is derived from mes- 7 Laryngotracheal Bronchial diverticulum buds enchyme in the caudal branchial arches whilst 8 the smooth muscle of the more distal oesopha- 9 gus develops from surrounding splanchnic mes- 4011 (i) Tracheo-oesophegeal (i) Traceo-oesophageal enchyme. Even in the fetus the oesophagus is of 1 fold septum vital functional importance, allowing swallowed 2 amniotic fluid to pass to the intestines for 3 absorption and placental transfer to maternal 4 blood. 5 Splenclinic 6 mesenchyme Oesophagus 7 c Laryngotracheal tube 8 Adult Oesophageal 9 Figure 1.1. a–c The embryological development of the Anatomy 5011 oesophagus. a Sagittal section of a 4-week-old embryo. 1 b–c The development of the tracheo-oesophageal septum and The oesophagus is a muscular tube protected at 2 separation of the oesophagus and laryngotracheal tube. its ends by the upper and lower oesophageal 311 2 3 THE ANATOMY AND PHYSIOLOGY OF THE OESOPHAGUS 111 sphincters. It commences as a continuation of Cervical Oesophagus 2 the pharynx at the lower border of the cricopha- 3 ryngeus muscle, at the level of the sixth cervical This begins at the lower border of the cricoid 4 vertebra (C6). The surface marking for this cartilage (C6) and ends at the level of the tho- 5 point is the lower border of the cricoid cartilage. racic inlet or jugular notch (T1). It lies between 6 It enters the chest at the level of the supraster- the trachea anteriorly and the prevertebral layer 7 nal notch and descends through the superior of cervical fascia posteriorly, deviating slightly 8 and posterior mediastinum along the front to the left at the level of the thyroid gland before 9 of the vertebral column. It passes though the returning to enter the thorax in the midline 1011 oesophageal hiatus in the diaphragm at the (Figure 1.3). The recurrent laryngeal nerves run 1 level of the tenth thoracic vertebra to end at in a caudal direction either side of the oesoph- 2 the gastro-oesophageal junction. The surface agus in the tracheo-oesophageal groove. They 3 marking for this point is the left seventh costal innervate the laryngeal muscles and surgical 4 cartilage. The oesophagus measures 25–30 cm trauma to the nerve at this point results in an 5 in length although this varies according to the ipsilateral vocal cord palsy. More laterally lie the 6 height of the individual and in particular the lobes of the thyroid gland with the inferior 7 suprasternal–xiphoid distance. thyroid artery and the carotid sheath contain- 8 ing the carotid vessels and the vagus nerve. 9 Anatomical Relationships of the Thoracic Oesophagus 2011 Oesophagus 1 The upper thoracic oesophagus extends the 2 The oesophagus can be artificially divided from length of the superior mediastinum between 3 proximal to distal into cervical, thoracic and the thoracic inlet and the level of the carina (T5). 4 abdominal segments [3] (Figure 1.2). The middle and lower thoracic oesophagus lies 5 6 7 8 9 3011 Cervical oesophagus 1 Trachea 2 3 Upper thoracic oesophagus 4 Azygos vein 5 Aorta 6 7 Middle thoracic oesophagus 8 Pulmonary artery 9 4011 Oesophagus 1 2 3 4 Lower thoracic 5 oesophagus Lower 6 Oesophagus 7 Diaphragm 8 9 Abdominal oesophagus 5011 1 2 311 Figure 1.2. The divisions and anatomical relations of the oesophagus. 3 4 1 · UPPER GASTROINTESTINAL SURGERY R L 1111 Thyroid 2 3 Trachea 4 Recurrent laryngeal nerve ⎧ 5 ⎨ Comon carotid artery 6 Carotid sheath Interior jugular vein 7 ⎩ Vagus nerve 8 Oesophagus 9 1011 Figure 1.3. Cross-section of the oesophagus in the lower neck. 1 2 3 in the posterior mediastinum subdivided by the mediastinum. It is here that the duct or its 4 midpoint between the tracheal bifurcation and radicals may be inadvertently damaged during 5 the oesophagogastric junction (Figure 1.2). mobilisation of the oesophagus, resulting in a 6 In the superior mediastinum the upper thor- chylothorax [4]. The duct then ascends, passing 7 acic oesophagus maintains close contact with behind the oesophagus to lie on its left side in 8 the left mediastinal pleura and posteriorly with the superior mediastinum. The oesophagus ini- 9 the prevertebral fascia. At this level the oesoph- tially lies to the right of the descending aorta but 2011 agus is indented by the arch of the aorta on its crosses it during its descent to lie anterior and 1 left side and crossed by the azygos vein on on its left side as it approaches the diaphragm. 2 its right side. As it descends into the posterior 3 mediastinum it is also crossed anteriorly and Abdominal Oesophagus 4 indented by the left main bronchus and crossed 5 by the right pulmonary artery (Figure 1.2).
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