Lung Alveoli - Location of Alveolar Ducts and Alveolar Sacs
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Lung Alveolus Structure – Lung Alveoli Anatomy

A magnified view of an alveolar sac
- About 95% of the alveolar surface consists of simple squamous epithelial
type I cells, and the remaining 5% is occupied by
type II cells (or septal cells).
- These large, rounded cells are located between the type I cells and
secrete the pulmonary surfactant. The complex of phospholipids and proteins in the surfactant reduces surface tension inside the alveoli, which keeps the alveolar walls from sticking together as they deflate during exhalation.
- Small openings called
alveolar pores perforate the interalveolar wall and allow air to pass between alveoli. They provide alternative routes to and from the alveoli if an obstruction occurs.
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- A network of
capillaries and many supportive collagen and elastic fibers are found in the narrow interstitial spaces that separate the alveoli.
- Numerous
macrophages (or dust cells) protect the lungs from damage. click
here to see a histological demonstration of the alveoli
- Macrophages (dust cells)
move about the air spaces and between the alveoli, where they remove (engulf) inhaled particles, foreign invaders, and other types of harmful substances.