• Hormones that act by binding to intracellular receptors: Many lipid-soluble hormones pass through the plasma membrane by diffusion to interact with receptors in the cytosol or the nucleus. The resulting hormone-receptor complexes bind specifically to regulatory elements in DNA, thereby affecting the expression of specific target genes. Hormones of this type include steroids (e.g., estrogen, progesterone, glucocorticoids), retinoids (vitamin A), and thyroxine.
Endocrine diseases generally are caused by: (1) underproduction or overproduction of hormones, with associated biochemical and clinical consequences; (2) end-organ resistance to the effects of a hormone; or (3) neoplasms, which may be nonfunctional or may be associated with overproduction or underproduction of hormones. In many settings, the study of endocrine diseases relies heavily on biochemical measurements of the levels of hormones, their regulators, and other metabolites.
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The pituitary gland is a small, bean-shaped structure that lies at the base of the brain within the confines of the sella turcica. It is intimately related to the hypothalamus, with which it is connected by a stalk, composed of axons extending from the hypothalamus, and a rich venous plexus constituting a portal circulation. Along with the hypothalamus, the pituitary has a central role in the regulation of most of the other endocrine glands. The pituitary is composed of two morphologically and functionally distinct components: the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis). Diseases of the pituitary, accordingly, can be divided into those that primarily affect the anterior lobe and those that primarily affect the posterior lobe.
The anterior pituitary, or adenohypophysis, produces trophic hormones that stimulate the production of hormones from the thyroid, adrenal, and other glands. The anterior pituitary is composed of epithelial cells derived embryologically from the developing oral cavity. In routine histologic sections, a colorful array of cells containing basophilic cytoplasm, eosinophilic cytoplasm, or poorly staining (chromophobic) cytoplasm is present (
Fig. 20.1 ). Detailed studies using electron microscopy and immunohistochemical techniques have demonstrated that the staining properties of these cells are related to the presence of different polypeptide hormones within their cytoplasm that control the activity of other endocrine glands. The release of these pituitary hormones is under the control of factors produced in the hypothalamus; while most hypothalamic factors are stimulatory and promote pituitary hormone release, others (e.g., somatostatin and dopamine) are inhibitory (
Fig. 20.2 ). Rarely, signs and symptoms of pituitary disease may be caused by overproduction or underproduction of hypothalamic factors, rather than a primary pituitary abnormality.
Symptoms and signs of pituitary disease fall into the following categories:
Fig.20.1Normalanteriorpituitarygland.Theglandispopulatedbyseveraldistinctcelltypesthatexpressdifferentpeptidehormones.Thesehormonesarebasophilic(blue),eosinophilic(red),ornonstaininginroutinesectionsstainedwithhematoxylinandeosin,whichallowsthevariouscelltypestobeidentified.Notealsothepresenceofafinereticulinnetworkbetweenthecells.
Hyperpituitarism related effects: Hyperpituitarism arises from excessive secretion of trophic hormones. It most often results from an anterior pituitary adenoma but also may be caused by other pituitary and extrapituitary lesions, as discussed later. The symptoms and signs of hyperpituitarism are discussed in the context of individual tumors later in the chapter (see
Table 20.1