Lower airway

Also known as the voice box, the larynx is located between the base of the tongue and the upper end of the trachea. Its primary function is to allow airflow between the pharynx and the trachea, protect against aspiration, and generate sound for speech.

The larynx comprises nine cartilages, providing structural support and facilitating its functions. These cartilages are further categorized as single or paired.

The largest of the larynx cartilages, the thyroid cartilage forms the prominent Adam's apple structure. It is a single cartilage, unlike the paired arytenoids or the epiglottis.

This signet ring-shaped cartilage lies beneath the thyroid cartilage in the larynx. It is essential for the stability and proper functioning of the voice box.

A broad, spoon-shaped cartilage that acts as a protective flap over the trachea during swallowing. It prevents food and liquids from entering the airway while you eat.

These paired, pyramid-shaped cartilages play a vital role in voice production. They attach to the vocal cords and move to adjust vocal cord tension and therefore, the pitch of your voice.

These are smaller cartilages, the Corniculate and Cuneiform, that are paired and contribute to stiffening the glottic folds, ensuring they are strong and effective.

The larynx's inner lining, a mucous membrane, forms folds, these are known as vocal cords. The upper folds are called false vocal cords and the lower ones, true vocal cords, have a vocal ligament.

The space between the true vocal cords is known as the glottis. It is a key element in vocalization, allowing the passage of air for speech and other sounds.

The movement of air through the larynx is a carefully coordinated process. During inhalation, the vocal cords move apart (abduct) to allow air in. During exhalation, they partially come together (adduct) maintaining a slightly open glottic space.

This is a maneuver that seals the larynx, closing the glottis. This technique serves to increase pressure within the chest cavity during activities like lifting, coughing, or straining.

The airway branching pattern from the trachea to the bronchioles can be described in generations or orders. Each generation is characterized by structural and functional differences in the airways.

The tracheobronchial tree consists of three layers: the epithelial lining, the lamina propria, and a cartilaginous layer. These layers collaborate to ensure the smooth functioning of the airways.

The inner lining of the airways is comprised of pseudostratified ciliated columnar epithelium. This type of epithelium gradually decreases in height as the airways get smaller.

The mucus blanket is a vital component of the tracheobronchial tree. Composed mainly of water, it serves to trap foreign particles, dust, and pathogens. It has two layers: Sol, which is less viscous, and Gel, more viscous.

Mast cells reside in the lamina propria of the airways. These cells play a crucial role in the immune response by releasing mediators that influence bronchial tone, causing constriction or relaxation of airways.

Cellular immunity involves sensitized lymphocytes attacking and destroying foreign invaders. Humoral immunity, on the other hand, involves the production of antibodies (like IgE, IgG, and IgM) that bind to and neutralize pathogens.

The trachea, the largest airway, is about 11 to 13 cm long and has a diameter of about 2.5 cm. It's comprised of 15 to 20 c-shaped rings of cartilage, ensuring it remains open for air passage.

The trachea divides into right and left main stem bronchi at the carina. The right bronchus is shorter and wider than the left and is at a 25-degree angle, while the left bronchus is at a 40-60-degree angle. These differences in size and angle contribute to the higher incidence of foreign objects lodging in the right bronchus.

Between generations 10 and 15 of airway branching, the bronchioles begin. These airways lack cartilage and are surrounded by spiral muscle fibers, giving them less rigidity.

These are the smallest air passages, measuring about 0.5mm in diameter. These airways have a cuboidal epithelium, lack cilia, and are devoid of mucus glands.

The bronchial arteries, originating from the aorta, supply blood to the airways of the lungs. The majority of the venous blood, about 2/3, flows to the left atrium via the pulmonary veins. This results in a phenomenon called venous admixture.