Stratified Squamous Epithelium Tutorial
Please read Unit 1 – Introduction to Epithelial Tissues prior to completing the activities in this chapter.
Introduction to Stratified Squamous Epithelium
Stratified squamous epithelium is composed of many layers of cells (stratified tissue organization) with only the bottom layer of cells (known as basal cells) contacting the basement membrane. Basal cells are typically large with a roundish shape and act as epithelial stem cells as they continually divide by mitosis and push older cells “up” toward the apical surface. As cells move toward the apical surface, they gradually flatten and take on a squamous shape (thin, roundish pancake shape) and become densely packed together. Many of the stratified squamous cells also become metabolically inactive and die as they move toward the apical surface where they are eventually shed (or sloughed off) by mechanical forces. Another characteristic of stratified squamous epithelium is that the bottom layers of cells (near the basement membrane) appear relatively dark with large darkly stained nuclei, while dead, squamous-shaped cells near the apical surface appear much lighter with less visible nuclei.
Since stratified squamous epithelium is relatively thick with densely packed dead cells near the apical surface, it gives the tissue properties of toughness, resistance to friction, and protection from chemical exposure and pathogenic microbes. Therefore, stratified squamous epithelium is found in body locations requiring resistance to friction and exposure to harsh conditions. Furthermore, stratified squamous epithelium can be classified as keratinized or nonkeratinized due to the presence or absence of a tough, fibrous protein known as keratin. Stratified squamous cells near the apical surface of the epidermis (outer layer of skin) are packed with keratin fibers, so stratified squamous epithelium of the skin is referred to as keratinized. Keratin gives epidermal cells added resistance to mechanical forces and desiccation (drying out) and helps prevent excessive water loss through the skin. Nonkeratinized stratified squamous (without keratin) is less resistant to extreme conditions and desiccation and must stay moist to maintain structural integrity. Therefore, nonkeratinized stratified squamous forms the moist endothelial linings of the mouth, pharynx, esophagus, rectum, and vagina.
Tutorial: Use the image slider below to learn more about the characteristics of stratified squamous epithelium.
Microscopy: Use the image slider below to learn how to use a microscope to identify and study nonkeratinized stratified squamous epithelium lining the esophagus.
Microscopy: Use the image slider below to learn how to use a microscope to identify and study keratinized stratified squamous epithelium composing the epidermis of skin.
Tutorial: Use the hotspot image below to learn more about the characteristics of nonkeratinized stratified squamous epithelium lining the esophagus.
Tutorial: Use the hotspot image below to learn more about the characteristics of keratinized stratified squamous epithelium composing the epidermis of skin.
