Glands are classified not only by their structure but also by the nature of their secretions. Serous (SEER-us) glands produce relatively thin, watery fluids such as perspiration, milk, tears, and digestive juices. Mucous glands, found in the tongue and roof of the mouth among other places, secrete a glycoprotein called mucin (MEW-sin). After it is secreted, mucin absorbs water and forms the sticky product mucus. (Note that mucus, the secretion, is spelled differently from mucous, the adjective form of the word.) Mixed glands, such as the two pairs of salivary glands in the chin, contain both serous and mucous cells and produce a mixture of the two types of secretions. Cyto-genic33 glands release whole cells. The only examples of these are the testes and ovaries, which produce sperm and egg cells.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.