Component composition

The epithelium lining respiratory passageways begins as pseudostratified columnar with cilia and goblet cells, commonly referred to as respiratory epithelium. A prominent basement membrane is also a common feature. The epithelium gradually decreases in height, with reduced cilia and goblet cells, transitioning through simple cuboidal to finally simple squamous in alveoli.

The epithelium lining respiratory passageways begins as pseudostratified columnar with cilia and goblet cells, commonly referred to as respiratory epithelium. A prominent basement membrane is also a common feature. The epithelium gradually decreases in height, with reduced cilia and goblet cells, transitioning through simple cuboidal to finally simple squamous in alveoli.

The epithelium lining respiratory passageways begins as pseudostratified columnar with cilia and goblet cells, commonly referred to as respiratory epithelium. A prominent basement membrane is also a common feature. The epithelium gradually decreases in height, with reduced cilia and goblet cells, transitioning through simple cuboidal to finally simple squamous in alveoli.

The epithelium lining respiratory passageways begins as pseudostratified columnar with cilia and goblet cells, commonly referred to as respiratory epithelium. A prominent basement membrane is also a common feature. The epithelium gradually decreases in height, with reduced cilia and goblet cells, transitioning through simple cuboidal to finally simple squamous in alveoli.

A lamina propria, located beneath the epithelium, consists of loose connective tissue with many blood vessels that aid in temperature regulation of the air.

In a respiratory passageway, the lamina propria may possess an interlacing meshwork of smooth muscle or an elastic lamina of longitudinally arranged elastic fibers. This layer is lacking, however, in the nasal cavities, pharynx and larynx.

The connective tissue layer beneath the smooth muscle and/or elastic lamina frequently contains mixed glands. Their secretions moisten the epithelium and, with cilia, form a mucociliary escalator to remove particulate matter and pollutants from inhaled air and transport them upward. These glands decrease in number and eventually disappear as the diameter of the passageways decreases.

Cartilage or bone supports the walls of the larger passageways, keeping the lumen open (patent). This supporting layer diminishes and eventually disappears as passageways become smaller in diameter.

Another layer of loose connective tissue surrounds the outer surface of the cartilage.