The lower respiratory system extends from the larynx to the alveoli. The first part is in the conducting zone, which carries air to the lungs. The last parts are in the respiratory zone, where gas exchange occurs.
The larynx is a triangular-shaped box containing vocal folds (cords) that vibrate to produce sound. The tension and length of the folds determines the pitch of the sound. Sound is modified by the mouth, tongue, pharynx, nasal cavities, and facial muscles. The vocal folds are open during inspiration.
The epiglottis is a flap guarding the entrance to the glottis of the larynx. It rises upward while breathing and lies downward during swallowing. The thyroid cartilage (Adam’s apple) is superior to the thyroid gland. It is U-shaped and incomplete posteriorly. The cricoid cartilage lies beneath the thyroid cartilage and forms a complete ring around the trachea . The arytenoid cartilage is the site of attachment of the vestibular folds (superior) and vocal folds (inferior). It is the inferior vocal folds that produce speech by vibrating as air passes by them.
The trachea is anterior to the esophagus. It forms a straight tube down to the bronchi. Tracheal cartilage is C-shaped to allow passage of food through the esophagus during swallowing. The trachealis muscle bridges the gap in tracheal cartilage. It can constrict the trachea during coughing. The trachea divides into primary bronchi that enter lungs. These branch into secondary and tertiary bronchi and finally into terminal bronchioles within the lung.
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