LUNGS

Histology of Bronchi: Primary, secondary, tertiary

• Epithelium – respiratory epithelium – columnar cells have gradual decrease in height, cilia & goblet cells.
• Lamina propria - gradual decrease in thickness & increase in number of elastic fibres.
• Glands – mucous & serous glands .
• Skeletal connective tissue – complete rings in primary, plates of cartilage in smaller bronchi.
• Muscle – several layers of circular smooth muscle.

Histology of Bronchioles

• Epithelium – Simple columnar with cilia & goblet cells.
• Lamina propria – gradual decrease in thickness & increase in number of elastic fibres.
• Glands – none.
• Skeletal connective tissue – none.
• Smooth muscle – decreasing numbers of smooth muscle cells.

Histology of Terminal bronchioles

• Epithelium – Simple cuboidal cilia free cells named Clara cells , some cells ciliated, goblet cells rare.
• Lamina propria - gradual decrease in thickness & increase in number of elastic fibres.
• Glands – none.
• Skeletal connective tissue – none.
• Smooth muscle – decreasing numbers of smooth muscle cells.

Histology of Respiratory bronchioles

• Epithelium – Low cuboidal, with few cilia; no goblet cells.
• Lamina propria - gradual decrease in thickness & increase in number of elastic fibres.
• Glands – none.
• Skeletal connective tissue – none.
• Smooth muscle – decreasing numbers of smooth muscle cells.

Histology of Alveolar ducts & sacs

• Epithelium – some low cuboidal, no cilia.
• Lamina propria - gradual decrease in thickness & increase in number of elastic fibres.
• Glands – none.
• Skeletal connective tissue – none.
• Smooth muscle – decreasing numbers of smooth muscle cells.

Histology of Alveoli

• Epithelium – mostly simple squamous (type 1) – some low cuboidal ( type 2 ) in septa.
• Lamina propria very thin with interstitium rich in capillaries & elastic fibres.
• Glands – none.
• Skeletal connective tissue – none.
• Smooth muscle – none.