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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Paraganglia are groups of cells that originate from the neural crest tissues. They are described as two different types. One type is found inside the adrenal medulla and is responsible for the secretion of epinephrine and norepinephrine. The other type is located outside the adrenal glands and has an entirely different function. It is believed the second type is responsible for the detection of oxygen and carbon dioxide levels in the blood.
Other paraganglia are found in small pockets or groups mostly in the head and neck region. Several types have been identified. Type I are cells called "true paraganglia" and are the type located along nerve fibers or near ganglia of the central nervous system. Type II are "free paraganglia" and are found within adipose tissue of the heart. They do not show any definite connection to specific structures. Type III, the "interganglionic paraganglia" are located within the ganglia themselves. Finally, the type IV are the "Intramyocardic paraganglia" which are immunoreactive cells that lie near the myocardiocyte bundles (excitable myocardiac cell fibers that transmit action potentials).
One of the most interesting functions of the paraganglia is their role in triggering signals to the brain via the vagus nerve. When a person is sick, macrophages (a type of immune system cell) releases cytokines that let the hypothalmus part of the brain stimulate and immune reaction. The cytokines are too big to pass the blood-brain barrier, but, instead, they attach to pockets of paraganglion cells located along the vagus nerve. The paraganglioic cells have receptors for interleukin-1, one of the types of cytokines carried by the blood. In turn these cells release neurotransmitters the vagus nerve and help send the signal to the brain to stimulate the body's immune response.