Alveolus

This alveolus is associated with an alveolar duct and thus the tips of the interalveolar septa possess smooth muscle knobs.

This alveolus is associated with an alveolar duct and thus the tips of the interalveolar septa possess smooth muscle knobs

This alveolus is associated with an alveolar duct and thus the tips of the interalveolar septa possess smooth muscle knobs

This alveolus is associated with an alveolar duct and thus the tips of the interalveolar septa possess smooth muscle knobs

The interalveolar septum is lined by a simple squamous epithelium of Type I cells and cuboidal Type II septal cells. Septal cells produce secretory granules containing surfactant, a mixture of phospholipids and proteins. Their frothy appearance results from extraction of these components during tissue processing. Septal cells are more numerous than type I cells, but only cover 5% to 7% of the surface. Septal cells divide to replenish both their own cell line and type I cells. 1000x

The interalveolar septum is lined by a simple squamous epithelium of Type I cells and cuboidal Type II septal cells. Septal cells produce secretory granules containing surfactant, a mixture of phospholipids and proteins. Their frothy appearance results from extraction of these components during tissue processing. Septal cells are more numerous than type I cells, but only cover 5% to 7% of the surface. Septal cells divide to replenish both their own cell line and type I cells. 1000x

The air-blood barrier separates an alveolar space from a capillary lumen; it is the membrane through which oxygen and carbon dioxide diffuse. The barrier is formed by two layers of simple squamous epithelium, one lining the alveolus and the other lining the capillary, and their fused basal laminae.