Tonsils & Adenoids (Lymphoid Tissue) of the Pharynx
Lung alveoli: anatomy and structure
The alveoli of the lung are small air sacs that have extremely thin tissue walls. The alveoli have a large surface area and receive oxygen from the blood that goes through an exchange of gases, allowing carbon dioxide to be removed.
- The respiratory bronchioles inside a secondary pulmonary lobule gives rise to two or more alveolar ducts.
- Protruding from the thin walls of the alveolar ducts and respiratory bronchioles are many cup-shaped alveoli, each measuring about 0.2 – 0.5 mm in diameter.
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- At the distal end of an alveolar duct, the alveoli are arranged into grape-like clusters called alveolar sac. The alveoli share a common opening to the alveolar duct.
Lung Alveolus Structure – Lung Alveoli Anatomy
- 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.
- 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
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- 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.