Carina is situated at which level

Carina is located at the bifurcation of trachea at lower border of T4.carina is the lower margin of lowest cailaginous ring that is a keel-shaped process curving downwards and backwards between the bronchi.The mucous membrane lining the area is highly sensitive and is origin of the protective cough reflex. It is visible during bronchoscopy and hence is an impoant landmark.If lymph nodes here enlarge due to spread of bronchogenic cancer, the carina becomes flattened and distoed.Reference: Clinical Anatomy for students, a problem-solving approach, Neeta v Kulkarni, 2nd edition, page no.211,212