The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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Mucocutaneous junctions are transition points between dry skin and the wet mucous membranes, the tissues lining body orifices such as the mouth, anus, nostrils, urethra, and vagina.
Mucous membranes consist of epithelial tissue over a basement membrane, attached to a layer of connective tissue called the lamina propria. Epithelium is a type of tissue that is generally moist, often containing mucus-secreting goblet cells, and regenerates very quickly.
The skin also contains epithelial tissue, but in the outer layers, the cells have lost their nuclei and flattened out. They contain a horny substance called keratin, forming a protective covering for the body. The skin has hairs, sebaceous glands, and sweat glands, which are absent from the mucous membranes. At the mucocutaneous junction, the epithelial tissue transitions between the dry keratinized skin and the wet epithelium of the mucous membrane.
At mucocutaneous junctions such as that of the lip, where the mucous membrane is exposed to the air, a type of tissue called parakeratinized epithelium is seen. Parakeratinized epithelium is tougher and drier than the typical mucous membrane, such as is found inside the mouth, but its surface cells still retain their nuclei. It exhibits vascular papillae, elevations containing many tiny blood vessels, or capillaries. Because there are no glands in the lips, they are subject to excessive drying in the air unless they are kept moist by saliva.