Epiglottis
It is a cartilaginous structure at the posterior of the tongue that folds over the opening of the trachea during swallowing.

Anterior (Lingual) Surface – faces the tongue.
Stratified Squamous Non-Keratinized Epithelium
Posterior (Respiratory) Surface – faces the opening of the trachea.
Stratified Squamous Non-Keratinized Epithelium – initially covers the posterior surface.
Transition Zone – abrupt transition from stratified squamous non-keratinizing epithelium to pseudostratified epithelium with cilia and goblet cells.
Respiratory Epithelium – pseudostratified epithelium with cilia and goblet cells.
Lamina Propria – dense irregular connective tissue that supports the epithelium.
Sero-Mucous Glands – add moisture to the air and help trap contaminants.
Ducts – the latter duct is a rare example of stratified columnar epithelium.
Elastic Cartilage – a series of elastic cartilages provide semi-rigid support to the epiglottis.

Trachea
It is a tube that connects the larynx to the lungs allowing the passage of air. It is a fibromuscular tube supported by 15 to 20 “C”-shaped hyaline cartilages.

Respiratory Epithelium – pseudostratified columnar epithelium with cilia and goblet cells resting on a thick basement membrane.
Lamina Propria – dense irregular connective tissue that supports the epithelium.
Sero-Mucous Glands – add moisture to air and aid in trapping contaminants.
Tracheal Cartilage – partial cross-section of a single, “C”-shaped hyaline cartilage.
Trachealis Muscle – a smooth muscle that spans the ends of tracheal cartilages. They control the diameter of the trachea.
Adventitia – loose connective tissue.

Lung
It consists of airways and structures for gas exchange. The trachea divides into a primary bronchus for each lung. The smaller intrapulmonary airways are devoid of cartilage and glands in their walls.

Epithelium changes from pseudostratified columnar to simple, ciliated columnar epithelium as they decrease in diameter.
Club Cells – dome-shaped secretory cells with short microvilli. (Do not have cilia.)
Smooth Muscle – variable amounts present.
Terminal Bronchioles – conducting airways.
Epithelium changes from simple, ciliated columnar epithelium to the cuboidal epithelium.
Respiratory Bronchioles – a mixture of conducting epithelium and alveoli where respiration occurs. The epithelium is a mixture of simple columnar and simple cuboidal epithelia.
Club Cells – become more prominent.
Smooth Muscle – only small amounts are present.
Alveolar Ducts – arise from respiratory bronchioles and are passageways lined with alveoli and occasional regions of simple cuboidal epithelium.
Alveolar Sacs – spherical-like spaces with openings into multiple alveoli.
Alveoli – blind-ending sacs that are the final termination of the airways.
Simple Epithelium) – contains two types of pneumocytes resting on a thin basal lamina:
Type I – flattened, simple squamous epithelial cells.
Gas exchange occurs through these cells.
Type II – dome-shaped, cuboidal epithelial cells that project into the lumen.
Secrete surfactant that covers the alveolar surface and reduces surface tension.
Macrophages (or Dust Cells) – large, dark cells within alveoli that engulf dust particles, bacteria, and other pathogens.
Capillaries – dense network surround alveoli. They are usually seen in cross-section and can be identified by finding a red blood cell within a lumen next to an endothelial cell.
Smooth Muscle – often found at the ends of alveolar walls.