It functions in maintaining the basic processes of the body ranging from metabolism to growth. The endocrine system also functions in long-term behavior and works in conjunction with the nervous system in regulating internal functions and maintaining homeostasis (Mani et al., 1997).
Hormones.
Hormones are the chemical messengers released by specialized endocrine cells or specialized nerve cells called neurosecretory cells (Leshner, 1978). Hormones are released (chemically secreted) by the endocrine system glands into the body's fluids: most often into the blood or lymphatic system and transported throughout the body (Leshner, 1978). Hormones are specified by their different chemical structures, which can be classified into four categories: amines, small molecules originating from amino acids; prostaglandins, cyclic unsaturated hydroxyl fatty acids synthesized in membranes from 20 carbon fatty acid chains; steroid hormones, cyclic hydrocarbon derivatives synthesized in all instances from the precursor steroid cholesterol; and peptide and protein hormones, the largest and most complex hormones (Mani et al., 1997). Hormones communicate for the endocrine system and are responsible for maintaining and controlling cellular activity. Without hormones the body could not function (Leshner, 1997). There are five main categories of hormone effects on the central nervous system: feedback, through positive and negative feedback loops; activation, the activating effect on a specific pattern of behavior; organization, the organizing effect on the brain typically at a specific stage during development; neuromodulation, the inhibition and/or facilitation of neural activity; and general metabolic effects (Leshner, 1997).
Hormones regulate bodily functions and are specific in what responses they elicit. As hormones are released into the bloodstream they can only initiate responses in target cells, which are specifically equipped to respond (Morin & Dark, 1994).
