It consists of several layers of cells with only the superficial layer having tall columnar cells. Locations: distal portion of the urethra, parotid and mandibular ducts, lacrimal sac and lacrimal duct. It is a form of stratified epithelium found only in the urinary tract lines the ureter and urinary bladder. It is highly specialized to resist a great degree of stretch and to withstand the toxicity of urine. In relaxed state empty bladder it is consists of layers of cells, the basal layer is cuboidal in shape rests on thin basal lamina.
The intermediate layer consists of several layers of polyhedral or pear-shaped cells. 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.
Transitional epithelia are found in tissues such as the urinary bladder where there is a change in the shape of the cell due to stretching. Key Terms simple columnar : A columnar epithelium that is uni-layered. Keratinized : To produce or become like keratin. Licenses and Attributions. CC licensed content, Shared previously. This is an example of thin skin.
There are around layers of cells. It's difficult to see the basal lamina in the region of the dividing cells, in the basal layer. Notice how the cells become more flattened towards the top apical layer. Cells at the top are flattened and have flattened nuclei - these cells are dying. The oesophagus is an example of a stratified squamous non-keratinising epithelium.
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