The stratified epithelia are formed by two or more layers of cells.
The image: an excretory duct of a salivary gland. This duct has been sectioned longitudinally and runs horizontally in the figure. Inside the duct, that is, inside its lumen, observe a homogeneous acidophilic substance stained in light pink – this is the secretory product of the gland being transported along the duct.
This is a large duct formed by the junction of several smaller, thinner excretory ducts. The wall of the smaller excretory ducts is a single layer of cells, a simple cubic epithelium. As the duct enlarges, the epithelium is replaced by a simple columnar epithelium. In even larger ducts, such as the one shown in the image, the epithelium of the duct becomes stratified.
The wall of the duct shown in the figure is made up of two layers of cells.
The inner layer, close to the basement membrane, is made of cuboidal cells, whose nuclei are indicated in light blue after using the mouse or clicking. The upper layer of the epithelium is formed by columnar cells whose nuclei will appear in dark blue. This epithelium is stratified cuboidal-columnar.
Salivary gland. Hematoxylin and eosin. Medium magnification.
