Terminal Bronchioles
description
Transcript of Terminal Bronchioles
Terminal Bronchioles
• Lined by simple ciliated columnar epithelium without goblet cells
• No cartilages, glands
Respiratory Bronchioles
• Branches of terminal bronchioles• Give rise to alveolar sacs, alveolar ducts, and
alveoli• Not sites of actual gas exchange• Lining epithelium: simple cuboidal, non-
ciliated epithelium• Some Clara cells
Alveolar Ducts
• Branch of from the walls of respiratory bronchioles
• Conical, thin-walled tubes• Lined by simple squamous epithelium• Give rise to numerous alveolar sacs and alveoli
that the openings practically occupy the entire wall of the duct
Alveolar Sacs and Alveoli
• Sites of actual exchange of gases between blood and inspired air
• Arise from either respiratory bronchioles or alveolar ducts
• Thin-walled polyhedral sacs• Open on one side – allow entry of air from the
respiratory bronchioles or alveolar ducts
Alveolar Sacs and Alveoli
• Around 300 million• Packed so closely that each alveolus does not
have a separate wall• Adjacent alveoli share a common wall
(interalveolar septum)
Interalveolar Septum
• Consists of thin supporting layer of connective tissue covered on either side by simple squamous epithelia
• Alveolar pores – allow direct communication between the cavities of adjacent alveoli
Interalveolar Cells
• Type I (pulmonary epithelial cell, small alveolar cell, pneumonocyte type I cell)
• Type II (great alveolar cell, pneumonocyte type II cell)
Type I Interalveolar Cell
• Less numerous but cover a majority of the alveolar surface area (> 95%)
• Squamous or flattened cells• Form the structure of the alveolar wall
Type II Interalveolar Cell
• Secrete pulmonary surfactant – reduces alveolar surface tension, thus prevents collapse of alveoli at the end of expiration
• Cuboidal or round cells
Pulmonary Alveolar Macrophages
• “Dust cells” • Most numerous cells in alveoli• Float freely in alveoli• Phagocytes
Blood-Air Barrier
• Ultra-thin structure separating the blood in a pulmonary capillary from the air in the alveolus
• Consists of:– Pulmonary epithelial cell– Basal lamina of the alveolar epithelium– Basal lamina of the capillary endothelium– Capillary endothelial cell