Secretions of the GI tract share several common features. A given secretion originates from individual groups of cells (e.g., acinar cells in the salivary gland) before pooling with other secretions. Secretions often empty into small ducts, which in turn empty into larger ducts, which empty into the lumen of the GI tract. Such a ductal system serves as a conduit for secretions from the salivary glands, pancreas, and liver, and modifies the primary secretion. Carbonic an-hydrase, an enzyme present in gastric, pancreatic, and intestinal cells, is involved in the formation of GI secretions.
An acinus and associated ductal system from the human submandibular gland. (Modified from Johnson LR, Christensen J, Jackson MJ, et al. eds. Physiology of the Gastrointestinal Tract. New York: Raven, 1987.)
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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.