Principles of Endocrinology

Cells in multicellular organisms must adopt specialized functions. By forming organs, cells can take on specialist functions, which would not be possible in individual cells; functions such as the conversion of food sources to energy (digestion), locomotion (running, jumping, flying), and the processing of more complex information signals (sight, hearing, touch, thought), as well as their storage (learning, memory). The coordination of all of these specialized functions within an organism is essential, as is the exchange of information between all of the different organs and their regulation by the brain. The brain transmits messages by two efferent pathways, through the nervous and the endocrine systems. These two are closely linked, and some “glands” (the hypothalamus, posterior pituitary, and adrenal medulla) histologically are derived from the nervous system. The transmission of impulses through the nervous system proceeds by way of “neurotransmitters” that are in themselves classical hormones (e.g., noradrenaline). For further reading, see, for example, Bentley (1980), Brown (1994), and Williams (1996).