Notes on The Upper Airways (Pages 1-5)
The Upper Airways
The upper airways consist of the nose, oral cavity, pharynx, and larynx.
Primary functions of the upper airways:
(1) act as a conductor of air
(2) humidify and warm or cool the inspired air
(3) prevent foreign materials from entering the tracheobronchial tree
(4) serve as an important area involved in speech and smell
The Nose
Primary functions of the nose:
filter, humidify, and condition (warm or cool) inspired air
site for the sense of smell
generate resonance in phonation
Anatomy of the nose (outer and inner structures):
Outer portion (bridge) is formed by the nasal bones and the frontal process of the maxilla.
Lower two‑thirds consist of:
lateral nasal cartilage
greater alar cartilage
lesser alar cartilages
septal cartilage
fibrous fatty tissue
Internal nasal septum partitions the nasal cavity into two chambers; posteriorly formed by the perpendicular plate of the ethmoid and the vomer; anteriorly by the septal cartilage.
Roof of the nasal cavity: formed by the nasal bones, the frontal process of the maxilla, and the cribriform plate of the ethmoid.
Floor of the nasal cavity: formed by the palatine process of the maxilla and by the palatine bones (the same bones that form the hard palate).
The posterior section of the nasal cavity floor is formed by the superior portion of the soft palate of the oral cavity (a flexible mass of densely packed collagen fibers).
Air entry: air enters the nasal cavity through the nares (nostrils) created by septal cartilage and alar regions.
Vestibule: air first passes through a slightly dilated vestibule containing vibrissae (hair follicles) that filter air; the vibrissae are the first line of defense for the tracheobronchial tree.
Epithelium:
Anterior one‑third of the nasal cavity is lined by stratified squamous epithelium (nonciliated).
Posterior two‑thirds is lined by pseudostratified ciliated columnar epithelium, with cilia moving mucus toward the nasopharynx.
Olfactory region: located in the roof of the nasal cavity (olfactory epithelium) for smell.
Flow and filtration context are illustrated in Figures 1‑1, 1‑2, 1‑3, and 1‑6A/B.
Nasal Flaring and Alar Collapse (Clinical Connection 1-on)
Nasal flaring: widening of the nostrils during periods of respiratory difficulty; a classic sign of respiratory discomfort, especially in the newborn.
Mechanism:
During respiratory distress (e.g., increased airway resistance such as asthma or stiffer lungs such as pneumonia), the patient generates a greater than normal negative pressure during inspiration to pull air into the airways more rapidly.
This negative pressure augments gas flow by widening the nostrils.
Associated conditions with nasal flaring: respiratory distress syndrome of the newborn, pneumonia, acute asthma, and any airway obstruction.
Clinical implication: aggressive respiratory therapy should be activated to increase arterial oxygen levels.
Alar collapse (the opposite): an important sign of nasal obstruction.
Nasal obstruction forces mouth breathing, contributes to snoring, and is associated with obstructive sleep apnea (OSA).
Epithelium of the Conducting Airways (Figure 1-6)
A. Stratified squamous epithelium: several cell layers; located in the anterior portion of the nasal cavity, oral cavity, oropharynx, and laryngopharynx.
B. Pseudostratified ciliated columnar epithelium: appears stratified because nuclei are at different levels; contains cilia and goblet cells; lines the posterior two‑thirds of the nasal cavity and the tracheobronchial tree.
C. Simple cuboidal epithelium: single layer of cube‑shaped cells; found in the bronchioles.
D. Simple squamous epithelium: single layer of thin, flattened cells with broad and thin nuclei; substances (e.g., O2 and CO2) readily pass; lines the walls of the alveoli and surrounding pulmonary capillaries.
Laryngopharynx (Hypopharynx)
Location: lies between the base of the tongue and the entrance to the esophagus.
Lined with nonciliated stratified squamous epithelium.
Epiglottis: the upper part of the larynx; positioned directly anterior to the laryngopharynx.
Aryepiglottic folds: mucous membrane folds that extend around the margins of the larynx from the epiglottis; function as a sphincter during swallowing.
Visualization: clinically, major structures of the laryngopharynx are observed from above using a laryngoscope, particularly noting the proximity of the epiglottis, vocal cords, and esophagus, when the patient is supine.
Innervation and reflexes:
Sensory innervation: ninth cranial nerve (glossopharyngeal, IX).
Motor innervation: tenth cranial nerve (vagus, X).
When stimulated, these nerves coordinate the pharyngeal reflex (gag or swallowing reflex) to prevent aspiration of foods/liquids and to prevent the base of the tongue from falling back and obstructing the laryngopharynx, even in a person who is asleep in the supine position.
The Larynx
The larynx (voice box) is located between the base of the tongue and the upper end of the trachea.
It is commonly described as a vestibule opening into the trachea from the pharynx.
Functions:
(1) acts as a passageway of air between the pharynx and the trachea
(2) enables speech
(3) serves as a protective mechanism against aspiration of solids and liquids
(4) generates sounds
Cartilages of the Larynx
The larynx contains a framework of cartilages (Figure 1-19):
Single cartilages (3): thyroid$, cricoid$, and epiglottis
Paired cartilages (3 pairs): arytenoid$, corniculate$, and cuneiform cartilages
Support and innervation:
Cartilages are held in position by ligaments, membranes, and intrinsic and extrinsic muscles.
The interior of the larynx is lined with mucous membrane.
Thyroid cartilage:
Largest cartilage; commonly called the Adam’s apple.
A double‑winged structure that covers the anterior portion of the larynx.
The superior border features a V‑shaped thyroid notch.
The upper portion is suspended from the larynx by the thyrohyoid membrane to the hyoid bone.
Hyoid bone:
Technically, the hyoid bone is not part of the larynx, but it is connected via the thyrohyoid membrane to the thyroid cartilage and helps suspend the larynx.
Epiglottis: positioned as the upper part of the larynx and related to the laryngopharynx.
Vallecula epiglottica: an important anatomical landmark used during endotracheal intubation to guide placement of the tube into the trachea.
Note: The text describes the larynx and surrounding structures in relation to the epiglottis, aryepiglottic folds, and the base of the tongue to provide context for airway management.