<prompt> Second constriction of oesophagus lies at the level ofWhere aortic arch crossesBronchiPharynxWhere esophagus pierces the diaphragm  <response>: A Where aortic arch Crosses 282-BDC-16tmCONSTRICTIONSNormally the oesophagus shows 4 constrictions at the following levels1. At its beginning 15 cm6 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 cm15 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 Laimers 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 