Question

why the alveoli are flexible

Answer 1

great alveolar epithelial cells: The rest of the 5% of the alveolar surface area is covered by large, cuboid to round type-2 epithelial cells, responsible for secreting pulmonary surfactant so the lungs can maintain their elastic recoil property.

Answer 2

Alveolar bone

Alveolar bone is very flexible and constantly remodels to accommodate the changing shape and size of the dental structures it contains. Alveolar bone can be divided into two main parts: a thin layer of compact (radiodense) bone (the ‘cortex’ of alveolus) that lines the alveolus proper, in which Sharpey's fibers insert, that is radiographically termed the lamina dura (lamina dura denta). This area is radiographically detectable (but not on computed tomography) as a thin radiodense line in brachydont teeth but due to irregularities of the periphery of some normal equine cheek teeth, this feature is not always obvious on lateral radiographs of equine teeth (Fig. 5.37). Secondly, the main alveolar bone surrounding the lamina dura denta cannot be morphologically differentiated from the main bone of the mandible or maxilla in adult brachydont teeth.1However, recent studies have shown that in horses, the alveolar bone beneath the lamina dura remains spongy and porous throughout life – similar to the alveolar bone of developing children's teeth – probably a reflection of its constant remodeling as the equine teeth constantly erupt.2 This presents an area of anatomical weakness, which may explain why sequestration of the alveolar cortical bone can occur following oral extraction of cheek teeth. The most prominent aspect of the alveolar bone beneath the gingival margin (occlusally) is termed the alveolar crest.