This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anatomy & Physiology (Oesophagus), Subject name: Surgery
Location of First constriction of esophagus from the incisor tooth: 
Select and explain. 
A. 15 cm, B. 18 cm, C. 25 cm, D. 40 cm
A: 15 cm
Answer: A: 15 cm 
Explanation: Ans. (a) 15cmBailey and Love 26th ed. ch. 621982The esophagus has 3 constrictions in its vertical course, as follows:* The first constriction is at 15 cm from the upper incisor teeth, where the esophagus commences at the cricopharyngeal sphincter; this is the narrowest portion of the esophagus and approximately corresponds to the sixth cervical vertebra* The second constriction is at 25 cm from the upper incisor teeth, where it is crossed by the aortic arch and left main bronchus.* The third constriction is at 40 cm from the upper incisor teeth, where it pierces the diaphragm; the lower esophageal sphincter (LES) is situated at this level.