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C h a p t e r
31
Mechanisms
of Endocrine
Control
The Endocrine System
Hormones
Structural Classification
Hormone Synthesis
Hormone Transport and Clearance from the
Blood
Receptor Control of Hormone Function
Control of Receptor Number and Affinity
Receptor Activation and Signaling
Regulation of Hormone Levels
Hypothalamic-Pituitary Regulation
Feedback Regulation
Diagnostic Tests
Blood Tests
Urine Tests
Stimulation and Suppression Tests
Genetic Tests
Imaging Techniques
Endocrine System
9
U N I T
he endocrine system is involved in all of the
integrative aspects of life, including growth, sex
differentiation, metabolism, and adaptation to an ever-
changing environment. This chapter focuses on general
aspects of endocrine function, organization of the endo-
crine system, hormone receptors and hormone actions,
and regulation of hormone levels.
The Endocrine System
The endocrine system uses chemical messengers called
hormones
as a means of controlling the flow of infor-
mation between the different tissues and organs of the
body. It does not act alone, however, but interacts with
the nervous system to coordinate and integrate the activ-
ity of body cells. Each system can function alone or in
concert with other systems as a single neuroendocrine
system, performing the same general functions within
the body of communication, integration, and control.
Although both the endocrine and nervous systems
function in regulating body functions, the means and
speed of control used by these two systems are different.
The nervous system functions by means of neurotrans-
mitter molecules transported by neurons over a short
distance to muscles and glands that respond within mil-
liseconds (see Chapter 34). The endocrine system, on the
other hand, uses hormones released from glands into the
blood and transported throughout the body to influence
the activity of body tissues. Tissue and organ responses to
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