Nucleus of simple columnar epithelial cell basement

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Nucleus of simple columnar epithelial cell Basement membrane Air sacs of lungs Nuclei of squamous epithelial cells Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (400x). (a) Diagram: Simple squamous Nucleus of simple cuboidal epithelial cell Photomicrograph: Simple cuboidal epithelium in kidney tubules (400x). Simple cuboidal epithelial cells Basement membrane Connective tissue (b) Diagram: Simple cuboidal Simple columnar epithelial cell Basement membrane Nucleus of squamous epithelial cell Basement membrane FIGURE 3.18 Types of epithelia and their common locations in the body.
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Chapter 3: Cells and Tissues 89 Basement membrane Pseudo- stratified epithelial layer Stratified squamous epithelium Transi- tional epithelium Basement membrane Basement membrane (f) Diagram: Transitional Photomicrograph: Transitional epithelium lining of the bladder, relaxed state (500x); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine. Cilia Mucus of goblet cell Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (400x). (d) Diagram: Pseudostratified (ciliated) columnar Photomicrograph: Stratified squamous epithelium lining of the esophagus (300x). Nuclei Basement membrane Connective tissue (e) Diagram: Stratified squamous Basement membrane Stratified squamous epithelium Transitional epithelium Pseudo- stratified epithelial layer Basement membrane Connective tissue Connective tissue
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90 Essentials of Human Anatomy and Physiology squamous epithelium is found in sites that receive a good deal of abuse or friction, such as the esoph- agus, the mouth, and the outer portion of the skin (Figure 3.18e). Stratified Cuboidal and Stratified Columnar Epithelia Stratified cuboidal epithelium typically has just two cell layers with (at least) the surface cells be- ing cuboidal in shape. The surface cells of stratified columnar epithelium are columnar cells, but its basal cells vary in size and shape. Both of these epithelia are fairly rare in the body, being found mainly in the ducts of large glands. (Because the distribution of these two epithelia is extremely limited, they are not illustrated in Figure 3.18. They are described here only to provide a complete list- ing of the epithelial tissues.) Transitional Epithelium Transitional epithelium is a highly modified, stratified squamous epithe- lium that forms the lining of only a few organs the urinary bladder, the ureters, and part of the urethra. All these organs are part of the urinary system and are subject to considerable stretching (Figure 3.18f). Cells of the basal layer are cuboidal or columnar; those at the free surface vary in ap- pearance. When the organ is not stretched, the membrane is many-layered, and the superficial cells are rounded and domelike. When the organ is distended with urine, the epithelium thins, and the surface cells flatten and become squamous- like. This ability of transitional cells to slide past one another and change their shape (undergo
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