++
++
The hypothalamus and pituitary gland form a unit that exerts control over the function of several endocrine glands—thyroid, adrenals, and gonads—as well as a wide range of physiologic activities. This unit is highly conserved across vertebrate species and constitutes a paradigm of neuroendocrinology—brain–endocrine interactions. The actions and interactions of the endocrine and nervous systems, whereby the nervous system regulates the endocrine system and endocrine activity modulates the activity of the central nervous system, constitute the major regulatory mechanisms for virtually all physiologic activities. These neuroendocrine interactions are also important in pathogenesis. This chapter reviews the normal functions of the pituitary gland, the neuroendocrine control mechanisms of the hypothalamus, and the disorders of those mechanisms.
++
Nerve cells and endocrine cells, which are both involved in cell-to-cell communication, share certain characteristic features—secretion of chemical messengers (neurotransmitters or hormones) and electrical activity. A single chemical messenger—peptide or amine—can be secreted by neurons as a neurotransmitter or neural hormone and by endocrine cells as a classic hormone. Examples of such multifunctional chemical messengers are shown in Table 4–1. The cell-to-cell communication may occur by four mechanisms: (1) autocrine communication via messengers that diffuse in the interstitial fluid and act on the cells that secreted them, (2) neural communication via synaptic junctions, (3) paracrine communication via messengers that diffuse in the interstitial fluid to adjacent target cells (without entering the bloodstream), and (4) endocrine communication via circulating hormones (Figure 4–1). The two major mechanisms of neural regulation of endocrine function are direct innervation and neurosecretion (neural secretion of hormones). The adrenal medulla, kidney, parathyroid gland, and pancreatic islets are endocrine tissues that receive direct autonomic innervation (see Chapters 9, 10, and 11). An example of neurosecretory regulation is the hormonal secretion of certain hypothalamic nuclei into the portal hypophysial vessels, which regulate the hormone-secreting cells of the anterior lobe of the pituitary. Another example of neurosecretory regulation is the posterior ...