Stratified Squamous Epithelium

Stratified epithelium is named for the shape of the cells forming the outermost layers. Stratified squamous epithelium consists of many layers of cells, making this tissue relatively thick. Cells nearest the free surface are flattened the most, whereas those in the deeper layers, where cell division occurs, are cuboidal or columnar. As the newer cells grow, older ones are pushed farther and farther outward, where they flatten (fig. 5.6).

Surface of tissue Cilia

Nucleus Goblet cell

Basement membrane

Connective tissue

Figure 5.5

Pseudostratified columnar epithelium appears stratified because nuclei are at different levels (100x micrograph enlarged to 320x).

Keratin Level Blood

Surface of tissue

Connective tissue

Figure 5.6

Stratified squamous epithelium consists of many layers of cells (70x)

Surface of tissue

Squamous cells

Layer of reproducing cells

Basement membrane

Connective tissue

Figure 5.6

Stratified squamous epithelium consists of many layers of cells (70x)

Squamous cells

Layer of reproducing cells

Basement membrane

Blood Vessel With Intact Epithelium

Figure

Stratified cuboidal epithelium consists of two to three layers of cube-shaped cells surrounding a lumen (100x micrograph enlarged to 320x).

The outermost layer of the skin (epidermis) is stratified squamous epithelium. As the older cells are pushed outward, they accumulate a protein called keratin, then harden and die. This "keratinization" produces a covering of dry, tough, protective material that prevents water and other substances from escaping from underlying tissues and blocks chemicals and microorganisms from entering.

Stratified squamous epithelium also lines the oral cavity, throat, vagina, and anal canal. In these parts, the tissue is not keratinized; it stays soft and moist, and the cells on its free surfaces remain alive.

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