C. T4- T5.
Tracheal bifurcation corresponds to T4- T5.
- It is divided into the upper airways and lower airways.
The upper airways or upper respiratory tract includes the nose and nasal passages, paranasal sinuses, the pharynx(nasopharynx, oropharynx and laryngopharynx) , and the portion of the larynx above the vocal folds (cords).
The lower airways or lower respiratory tract includes the portion of the larynx below the vocal folds, trachea, bronchi (primary, secondary and tertiary), bronchioles (including terminal and respiratory), and lungs (including alveoli).
- In adult humans, the larynx is found in the anterior neck at the level of the C3–C6 vertebrae.
- In newborn infants, the larynx is initially at the level of the C2–C3 vertebrae
- Trachea bifurcates at Carina (at lower border of T4 vertebra at T4-T5 disc space) into right and left principal (primary) bronchi.