ANATOMY

Successful airway management requires detailed understanding of upper and lower airway structure and function.

UPPER AIRWAY

                The human airway has two openings: the nose and the mouth.  Remember: the floor of the nose is the roof of the mouth.  The nose leads to the NASOPHARYNX and the mouth leads to the OROPHARYNX.  Separated anteriorly by the PALATE, these two passages join posteriorly in the PHARYNX.  At the base of the tongue, the EPIGLOTTIS separates the OROPHARYNX and the LARYNGOPHARYNX/HYPOPHARYNX.  The LARYNX  extends from the lower part of the pharynx to the TRACHEA.

 

E =Epiglottis; VsF=vestibular fold (ligament); VL=vocal ligament; TA=transverse arytenoid; CtL=cricothyroid ligament; CC=cricoid cartilage.

LOWER AIRWAY

THE CONDUCTING ZONE

At the CARINA,  the trachea bifurcates into the RIGHT AND LEFT MAIN BRONCHI. The right and left main bronchi further branch into lobar/secondary bronchi (one to each lobe of the lung – thus, two on the left and three on the right), then divide again into segmental/tertiary bronchi and finally terminal bronchioles, which are the smallest airways without alveoli.  The segmental/tertiary bronchi are of particular importance because they supply each BRONCHOPULMONARY SEGMENT.

These structures make up the conducting airways and serve to lead inspired air to the gas-exchanging regions downstream.  The conducting airways contain NO ALVEOLI and, thus, do not take part in gas exchange. The conducting zone of the airway constitutes the anatomical dead space (150ml). 

THE RESPIRATORY ZONE

The terminal bronchioles divide into respiratory bronchioles which continue downstream as alveolar ducts.  While respiratory bronchioles have occasional alveoli budding from their walls, alveolar ducts are completely lined with alveoli/alveolar sacs.  There are over 300 million alveoli in the human lung and each alveoli is covered in an extensive network of capillaries.  “The Acinus” refers to the anatomical unit formed by the portion of lung distal to a terminal bronchiole. The respiratory zone makes up most of the lung (2.5-3L).

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