15.01 Introduction to the Endocrine System

Hormones, produced by endocrine glands, are important in regulating and integrating the bodies functions. They have roles in metabolism, fluid balance, growth, development and reproduction. Hormones are chemical messengers released by glands. Hormones act specifically and at low concentrations on their target receptors, which are distant from the releasing organ. Hormones can be subdivided into classes based on their chemical structure; steroid hormones, amino-acid derived hormones and peptide hormones. There are differences in the release and activity of hormones depending on their chemical type (Table 15.1).

The endocrine glands produce and release hormones into the bloodstream. They are usually transported by specialised hormone binding proteins. This increases the transport of the protein, decreases membrane transport (e.g. excretion in kidney, metabolism in liver, crossing of the blood brain barrier) and acts as a reservoir of the hormone in the blood. Only the unbound hormone can cross into cells and act at receptors.

The hormone insulin and the treatment of diabetes and obesity are covered in Chapter 14. This chapter considers drugs used to treat thyroid disorders, osteoporosis and other bone disorders, hyperparathyroidism, adrenal cortex disorders, infertility, and drugs that affect the hormones of reproduction