| The endocrine system provides communication between cells, tissues and organs. In higher species, such as humans, sophisticated control mechanisms are required to ensure optimal communication between cells, tissues, and organs. Along with the nervous system, the endocrine system provides this communication and is responsible for the regulation of a wide range of functions including growth, development, reproduction, homeostasis, and the response to external stimuli and stress. Failures in this communication channels are common and lead to many diseases of the endocrine system.
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| Several organs secrete hormones
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| Many organs in the body secrete biologically active compounds called endocrine hormones, which are transported via the bloodstream to other tissues or organs where they exert a biological effect. Some hormones, termed paracrine hormones, are made and act locally, affecting the tissue that synthesizes them. Others, termed autocrine hormones act on the cell that synthesized them or on neighboring cells of the same type. All of these hormones act by binding to specific receptors, either on the cell surface or within the target cell (see Chapter 38). It is this hormone-receptor interaction that triggers and coordinates a wide range of biological effects.
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| Negative feedback regulation is important for homeostatic control
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| In order to ensure tight homeostatic control, the final output of hormone action involves a complex feedback loop that regulates either further hormone synthesis or secretion, or hormone sensitivity (Fig. 37.1).
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| Several hormones may control one process, or one hormone may control several processes
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While it may be convenient to think of the endocrine system as being compartmentalized so that one hormone has control over one process, this is rarely the case. For example, at least four different hormones are involved in the regulation of plasma glucose concentration (see Chapter 20). Conversely, single hormones such as testosterone influence a range of metabolic processes.
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