L1 histo respi

Respiratory Epithelium

• Serous cells: non-ciliated secretory cells that secrete glycoproteins and lysozymes, contributing to the low viscosity of the periciliary fluid covering the bronchial epithelium.
• Clara cells (bronchiolar epithelial cells): non-ciliated columnar cells found in terminal and respiratory bronchioles, playing a major role in the metabolism of exogenous agents and acting as progenitor (stem) cells for bronchiolar epithelium.
• Small granule cells (DNEs): found throughout the airways, either as isolated cells or clusters, with dense core of granules, and having endocrine functions.

Nasal Cavity

• Composed of three regions: vestibule, nasal fossa, and paranasal sinuses.
• Vestibule: the dilated anterior portion of the nasal cavity, lined with skin (keratinized stratified squamous epithelium) and having fine short, stiff hairs (vibrissae) that prevent large dust particles from entering the respiratory passage.
• Nasal fossa: divided by a midline nasal septum into right and left nasal fossae, with the lateral wall containing bony projections (conchae).
  • Superior conchae lined by olfactory epithelium.
  • Middle and inferior conchae lined by respiratory epithelium.

Histology of the Respiratory Region of the Nasal Fossa

• Respiratory region formed of a mucosa with two layers: respiratory epithelium and lamina propria.
• Respiratory epithelium: pseudostratified ciliated columnar epithelium with goblet cells, brush (sensory) cells, basal stem cells, and small granule cells (DNEs).
• Lamina propria: richly vascularized connective tissue containing large arterial and venous plexuses, many seromucous glands, and lymphoid elements.

Histology of the Olfactory Region of the Nasal Fossa

• Occupies the roof of each nasal fossa.
• Histology: lined with olfactory mucosa formed of two layers: olfactory epithelium (smell receptor) and lamina propria.
• Olfactory epithelium: comprises three types of cells - olfactory cells (receptor cells), supporting columnar or sustentacular cells, and basal cells.

Paranasal Sinuses

• Air-filled cavities within the bone of the skull (frontal, maxillary, ethmoid, and sphenoid).
• Histology: the mucosa of paranasal sinus is formed of two layers - epithelium (respiratory epithelium with few goblet cells) and lamina propria (fused with periosteum of bones and housing seromucous glands and lymphoid elements).

Nasopharynx

• Continuous anteriorly with the nasal fossae and inferiorly with the oropharynx.
• Histology: the mucosa of the nasopharynx is formed of two layers - epithelium (respiratory epithelium) and lamina propria (containing glands and accumulation of single unencapsulated lymphatic tissue, pharyngeal tonsil).

Larynx

• Located between the pharynx and trachea.
• Histology: the mucosa of the larynx has two layers - epithelium (lined by respiratory epithelium) and lamina propria (containing laryngeal hyaline cartilages and elastic cartilage).
• Function: prevents food from entering the trachea during swallowing and produces voice.

Epiglottis

• A leaf-shaped flap of elastic cartilage located behind the tongue, at the top of the larynx.
• Histology: the mucosa of the epiglottis is formed of two layers - epithelium (non-keratinized stratified squamous epithelium on the lingual surface and pseudostratified ciliated columnar epithelium on the laryngeal surface) and lamina propria (containing thin plate of elastic cartilage, serous and mucous glands).
• Function: prevents food and water from entering the larynx and respiratory passage during swallowing.