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AC: adenylyl cyclase

ACTH: corticotropin, formerly adrenocorticotrophic hormone

CG: chorionic gonadotropin

CRH: corticotropin-releasing hormone

DA: dopamine

FSH: follicle-stimulating hormone, follitropin

GH: growth hormone

GHRH: growth hormone–releasing hormone

GnRH: gonadotropin-releasing hormone

GPCR: G protein –coupled receptor

hCG: human chorionic gonadotropin

5HT: 5-hydroxytryptamin serotonin

IGF-1: insulin-like growth factor 1

IGFBP: IGF-binding protein

IRS: insulin receptor substrate

LH: luteinizing hormone; lutropin

NPY: neuropeptide Y

OXTR: oxytocin receptor

POMC: pro-opiomelanocortin

PRL: prolactin

SC: subcutaneous

SHC: Src homology-containing protein

SHP2: Src-homology-2-domain-containing protein tyrosine phosphatase 2

SST: somatostatin

SSTR: SST receptor

TRH: thyrotropin-releasing hormone

TSH: thyroid-stimulating hormone, thyrotropin

VIP: vasoactive intestinal peptide


Endocrinology analyzes the biosynthesis of hormones, their sites of production, and the sites and mechanisms of their action and interaction. The term hormone is of Greek origin and classically refers to a chemical messenger that circulates in body fluids and produces specific effects on cells distant from the hormone’s point of origin. The major functions of hormones include the regulation of energy storage, production, and utilization; the adaptation to new environments or conditions of stress; the facilitation of growth and development; and the maturation and function of the reproductive system. Although hormones were originally defined as products of ductless glands, we now appreciate that many organs not classically considered as “endocrine” (e.g., the heart, kidneys, GI tract, adipocytes, and brain) synthesize and secrete hormones that play key physiological roles. In addition, the field of endocrinology has expanded to include the actions of growth factors acting by means of autocrine and paracrine mechanisms, the influence of neurons—particularly those in the hypothalamus—that regulate endocrine function, and the reciprocal interactions of cytokines and other components of the immune system with the endocrine system.

Conceptually, hormones may be divided into two classes:

  • Hormones that act predominantly via nuclear receptors to modulate transcription in target cells (e.g., steroid hormones, thyroid hormone, and vitamin D)

  • Hormones that typically act via membrane receptors to exert rapid effects on signal transduction pathways (e.g., peptide and amino acid hormones)

The receptors for both classes of hormones provide tractable targets for a diverse group of compounds that are among the most widely used drugs in clinical medicine.


Many of the classic endocrine hormones (e.g., cortisol, thyroid hormone, sex steroids, GH) are regulated by complex reciprocal interactions among the hypothalamus, anterior pituitary, and endocrine glands (Table 42–1). The basic organization of the hypothalamic-pituitary-endocrine axis is summarized in Figure 42–1.

Table 42–1Hormones that Integrate the Hypothalamic-Pituitary-Endocrine Axis

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