(A) (Where aortic arch Crosses) (282-BDC-16(tm))CONSTRICTIONSNormally the oesophagus shows 4 constrictions at the following levels1. At its beginning 15 cm/6 inch form the incisor teeth where it is crossed by cricopharyngeus muscles2. Where it is crossed by the aortic arch, 22,5cm /19 inch from the incisor teeth3. Where it is crossed by the left bronchus, 27.5cm /11 inch from the incisor teeth4. Where it pierces the diaphragm 37.5 cm/15 inch from the incisor teethOESOPHAGUS* About 25 cm long (10 inch)* The pharyngo-oesophageal junction is the commoned part of the alimentary canal except for the vermiform appendix* It passes through the diaphragm at the level of the 10th thoracic vertebra to join the stomachImportant features of esophagus* Epithelium is stralified squamous non * keratinized epithelium* Muscularis mucosa contains only longitudinal layer and no circular layer* Mucosa is the toughest and strongest layer *** Serosa is absent* Muscmaris extern is made up skeletal muscle fibre only in the upper ihird, smooth muscle only in the lower third and both types of muscle fibres in middle third. At uppen end the longitudinal coat split into two bundles and the triangular interval between them is called Laimer's triangle which is filled with circular muscle fibers* Extent of esophagus is -C6 -T i j* Trachea bifurcates at carina, at the level of lower border of T4 or T4-T5 disc spaces* Oesophageal opening transmits1. Oesophagus2. Gastric or vagus nerve3. Oesophageal branches of the left gastric artery. With some oesophageal veins* Arterial supply- Upper third -inferior thyroid artery **- Middle third - Oesophageal branches of the ** descending thoracic aorta- Lower third - Left gastric artery **