Upon completion of the chapter, the reader will be able to:
List the mediators and primary effects of pituitary hormones.
Identify clinical features of patients with acromegaly.
Discuss the role of surgery and radiation therapy for patients with acromegaly.
Select appropriate pharmacotherapy for patients with acromegaly based on patient-specific factors.
Identify clinical features of children and adults with growth hormone (GH) deficiency and select appropriate pharmacotherapy for these patients.
Recommend monitoring parameters necessary to assess therapeutic outcomes and adverse effects in patients receiving GH therapy.
List common etiologies of hyperprolactinemia.
Identify clinical features of patients with hyperprolactinemia.
Select appropriate pharmacologic and nonpharmacologic treatments for patients with hyperprolactinemia based on patient-specific factors.
PHYSIOLOGY OF THE PITUITARY GLAND
The pituitary, referred to as the “master gland,” is a small endocrine gland located at the base of the brain and is responsible for the regulation of many other endocrine glands and body systems. Growth, development, metabolism, reproduction, and stress homeostasis are among the functions influenced by the pituitary. Functionally, the gland consists of two distinct sections: the anterior pituitary lobe and the posterior pituitary lobe. The pituitary receives neural and hormonal input from the inferior hypothalamus via blood vessels and neurons.
The posterior pituitary is innervated by nervous stimulation from the hypothalamus, resulting in the release of specific hormones to exert direct tissue effects. The hypothalamus synthesizes two hormones, oxytocin and vasopressin. These hormones are stored and released from the posterior pituitary lobe. The anterior pituitary lobe is under the control of several releasing and inhibiting hormones secreted from the hypothalamus via a portal vein system. It synthesizes and secretes six major hormones. Figure 46–1 summarizes the physiologic mediators and effects of each of these hormones.
Hypothalamic–pituitary–target-organ axis. The hypothalamic hormones regulate the biosynthesis and release of eight pituitary hormones. Stimulation of each of these pituitary hormones produces and releases trophic hormones from their associated target organs to exert their principal effects. These trophic hormones regulate the activity of endocrine glands. Subsequently, increased serum concentration of the trophic hormones released from the target organs can inhibit both the hypothalamus and the anterior pituitary gland to maintain homeostasis (negative feedback). Inhibin is produced by the testes in men and the ovaries in women during pregnancy. Inhibin directly inhibits pituitary production of follicle-stimulating hormone (FSH) through a negative feedback mechanism. Melanocyte-stimulating hormone (MSH) produced by the anterior pituitary is not illustrated in the figure. (–), inhibit; (+), stimulate; ACTH, adrenocorticotropic hormone (corticotropin); ADH, antidiuretic hormone (vasopressin); CRH, corticotropin-releasing hormone; FSH, follicle-stimulating hormone; GABA, γ-aminobutyric acid; GH, growth hormone (somatotropin); GHIH, growth hormone–inhibiting hormone (somatostatin); GHRH, growth hormone–releasing hormone; GnRH, gonadotropin-releasing hormone; IGF-I, insulin-like growth factor-I; LH, luteinizing hormone; LHRH, luteinizing hormone–releasing hormone; PRH, prolactin-releasing hormone; T3, triiodothyronine; T4, thyroxine; TRH, thyrotropin-releasing hormone; TSH, thyroid-stimulating hormone (thyrotropin).
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