ABSTRACT
Study objectives Differentiate between the primary functions of the nervous system and the endocrine system Describe the biochemical and functional distinctions between steroid hormones, protein/peptide hormones, and amine hormones Explain the benecial effects of the binding of hormones to plasma proteins Explain how hormones are eliminated Distinguish between a trophic and a nontrophic hormone Describe the three types of hormone interactions Explain the two primary mechanisms by which hormones carry out their effects Describe how the effects of hormones are amplied Describe how the pituitary gland is formed during embryonic development Describe the anatomical and functional relationships between the hypothalamus and the pituitary gland Explain how negative feedback mechanisms limit the release of hormones from the adenohypophysis List the functions and describe the mechanisms that regulate the release of hormones from the neurohypophysis List the functions and describe the mechanisms that regulate the release of hormones from the adenohypophysis Discuss the functions and the factors that regulate the release of the following hormones: thyroid hormones, calcitonin, parathyroid hormone, aldosterone, cortisol, adrenal androgens, insulin, and glucagon
0. Introduction There are two major regulatory systems that contribute importantly to homeostasis: the nervous system and the endocrine system. In order to maintain relatively constant conditions in the internal environment of the body, each of these systems inuences the activity of all of the other organ systems. The nervous system coordinates fast, precise responses, such as muscle contraction. As such, the electrical impulses generated by this system are very rapid and of short duration (msec). The endocrine system regulates
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metabolic activity within the cells of the organs and tissues. In contrast to the nervous system, the endocrine system coordinates activities that require longer duration (hours, days) rather than speed. Examples of such activities include growth, the long-term regulation of plasma volume and blood pressure, and the coordination of menstrual cycles in females. The endocrine system carries out its effects through the production of hormones, chemical messengers that exert a regulatory effect on the cells of the body. Secreted from endocrine glands, which are ductless structures, hormones are released directly into the blood. They are then transported by the circulation to the tissues upon which they exert their effects. Because they travel in the blood, the serum concentrations of hormones are very low (10-11 to 10-9 M); therefore, these molecules must be very potent.
