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There are broad principles and concepts in endocrinology that the reader must understand. Familiarity with concepts such as negative feedback loops, hormone-receptor function, and hormone replacement therapy allows the physician to generalize what is learned in one area and apply it to others. This gives the ability to predict the effects of an endocrine abnormality or perturbation on downstream hormones and its subsequent clinical effects. Conversely, it also allows the clinician to consider a set of symptoms, work backward to develop a differential diagnosis, and test this by looking for laboratory abnormalities that are diagnostic for an endocrine disease. This chapter reviews many of these basic principles that are applicable across the field in order to provide groundwork for later chapters. Following a discussion of general hormone function and integration of endocrine systems, we will discuss the classification of hormones. Reviews of hormone synthesis, processing, and transport follow, and then we will outline the regulation of hormone secretion. Following this, we will discuss genetics for the endocrinologist, examine the evolving field of hormone receptors, and consider nontraditional endocrine systems. The clinical relevance of the preceding material is apparent in the section covering principles of endocrine disease. Finally, we will summarize important principles in endocrine testing.


The endocrine system consists of a dizzying number of hormones, and newly discovered ones are added to the list on a regular basis. The word “hormone” comes from the Greek word “ormaein” meaning to set in motion or to spur on. This is an apt derivation, because, as classically defined, hormones are chemicals secreted by one tissue that produce effects in distant tissues, leading to an array of physiologic responses. In addition to the classic sense, hormones may have local effects as discussed later in this chapter. In children, we can categorize hormones by the systems that they affect, including growth, reproduction, homeostasis, and energy regulation. Many hormones play roles in multiple categories, emphasizing the complex network of interactions and the redundancy built into these processes. Table 1–1 shows how selected endocrine systems fit into this categorization, illustrating this redundancy.

Table 1-1.Classes of Hormone Function With Selected Examples of Endocrine Systems

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