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Endocrinology |
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INTRODUCTION TO THE Endocrinology |
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Endocrinology is the study of hormones, their receptors
and the intracellular signalling pathways they invoke.
Distinct endocrine organs are scattered throughout the
body. These are organs that are largely or at least
famously devoted to secretion of hormones. In addition to
the classical endocrine organs, many other cells in the
body secrete hormones. Myocytes in the atria of the heart
and scattered epithelial cells in the stomach and small
intestine are examples of what is sometimes called the
"diffuse" endocrine system. If the term hormone is defined
broadly to include all secreted chemical messengers, then
virtually all cells can be considered part of the
endocrine system. |
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How is it that humans and animals maintain quite
constant blood concentrations of glucose throughout their
lives despite wildly varying frequencies of meals? If
your blood glucose concentration drops much below 1 mg per
ml, your neurons will begin to misbehave, leading
ultimately to coma and death. Yet skipping breakfast is
rarely life-threatening.
The answer is that a battery of chemical messengers -
hormones - are secreted into blood in response to
rises and falls in blood glucose concentration and
stimulate metabolic pathways that pull glucose
concentrations back into the normal range. |
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Two systems control all
physiologic processes:
- The nervous system exerts
point-to-point control through nerves, similar to
sending messages by conventional telephone.
Nervous control is electrical in nature and fast.
- The endocrine system broadcasts its
hormonal messages to essentially all cells by
secretion into blood and extracellular fluid. Like
a radio broadcast, it requires a receiver to get
the message - in the case of endocrine messages,
cells must bear a receptor for the hormone
being broadcast in order to respond.
As will be repeatedly demonstrated, the nervous
and endocrine systems often act together to regulate
physiology. Indeed, some neurons function as
endocrine cells |
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A final introductory comment is warranted. Pursuit of an
understanding of endocrinology is complicated by several
of its principles:
- All pathophysiologic events are influenced by
the endocrine milieu: There are no cell types,
organs or processes that are not influenced - often
profoundly - by hormone signaling.
- All "large" physiologic effects are mediated by
multiple hormones acting in concert: Normal growth
from birth to adulthood, for example, is surely
dependent on growth hormone, but thyroid hormones,
insulin-like growth factor-1, glucocorticoids and
several other hormones are also critically involved in
this process.
- There are many hormones known and little doubt
that others remain to be discovered.
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Consequently, endocrinology is presented here in two
ways. First, the major endocrine organs and the hormones
they produce are introduced, with delineation of major
effects. Second, an integrated approach to understanding
the multi-hormone control of several important phenomena
is provided. Importantly, a considerable amount of
endocrinology is incorporated into other sections.
Gastrointestinal hormones, for example, are discussed
throughout the section on pathophysiology of the
digestive system. |
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Disclaimer - The
contents of this site are for informational purposes
only. Always seek the advice of a qualified
physician for any doubts. |
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