Since stratified epithelium consists of two or more layers, the basal cells divide and push towards the apex, and in the process flatten the apical cells.
Stratified epithelia can be columnar, cuboidal, or squamous type. However, it can also have the following specializations:. In keratinized epithelia, the most apical layers exterior of cells are dead and lose their nucleus and cytoplasm. They contain a tough, resistant protein called keratin. This specialization makes the epithelium waterproof, and it is abundant in mammalian skin.
The lining of the esophagus is an example of a non-keratinized or moist stratified epithelium. Transitional epithelia are found in tissues that stretch and it can appear to be stratified cuboidal when the tissue is not stretched, or stratified squamous when the organ is distended and the tissue stretches.
It is sometimes called the urothelium since it is almost exclusively found in the bladder, ureters, and urethra. Privacy Policy. Skip to main content. Organization at the Tissue Level. Search for:. Epithelial Tissue. Characteristics of Epithelial Tissue The human body consists of four types of tissue: epithelial, connective, muscular, and nervous.
Learning Objectives Describe the primary functions and characteristics of epithelial tissue. Key Takeaways Key Points Epithelial tissue is composed of cells laid together in sheets with the cells tightly connected to one another. Epithelial layers are avascular, but innervated. Epithelial cells have two surfaces that differ in both structure and function.
Glands, such as exocrine and endocrine, are composed of epithelial tissue and classified based on how their secretions are released.
Key Terms epithelium : A membranous tissue composed of one or more layers of cells that form the covering of most internal and external surfaces of the body and its organs. Types of Epithelial Tissue Epithelial tissue is classified by cell shape and the number of cell layers. Learning Objectives Classify epithelial tissue by cell shape and layers.
Key Takeaways Key Points There are three principal cell shapes associated with epithelial cells: squamous epithelium, cuboidal epithelium, and columnar epithelium. There are three ways of describing the layering of epithelium: simple, stratified, and pseudostratified. Pseudostratified epithelium possesses fine hair-like extensions called cilia and unicellular glands called goblet cells that secrete mucus. This epithelium is described as ciliated pseudostratified epithelium.
Stratified epithelium differs from simple epithelium in that it is multilayered. It is therefore found where body linings have to withstand mechanical or chemical insult. In keratinized epithelia, the most apical layers exterior of cells are dead and and contain a tough, resistant protein called keratin. An example of this is found in mammalian skin that makes the epithelium waterproof. Simple secretory columnar epithelium lines the stomach and uterine cervix.
The simple columnar epithelium that lines the intestine also contains a few goblet cells. In histological slides of pseudostratified epithelium , it looks as though some of the cells are not in contact with the basal lamina, and the nuclei are at different levels. So it looks as though there is more than one layer of cells. However EM shows that all the cells contact the basal lamina, so this is a 'simple' epithelium. But it is called pseudostratified, because of its appearance.
Pseudostratified ciliated columnar epithelium containing goblet cells lines most of the major airways. Instead of being smooth, the inside of the intestine is folded and covered by millions of tiny projections called villi. On the image, you can see one fold on the right and parts of several villi sticking up from the surface of the fold. Simple columnar epithelium X Primate small intestine. At X you can begin to see the layer of simple columnar epithelium.
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