Hormones are chemical messengers released by endocrine cells or neurosecretory cells which regulate bodily functions and are highly specific in which tissues they react with and the response they elicit from those tissues (The Endocrine, 2005). There are four categories of hormones: amines, small molecules originating from amino acids, such as epinephrine and thyroid hormone; prostaglandins, cyclic unsaturated hydroxy fatty acids synthesized in membranes from 20-carbon fatty acid chains; steroids, cyclic hydrocarbon derivatives produced from the precursor steroid cholesterol, e.g. testosterone and estrogen; and peptide and protein hormones, the largest and most complex hormones, e.g. insulin.
There are many hormones that can influence behavior, the most significant being the gonadal, placental. thyroid, and adrenal hormones (Depression, 2003; The Endocrine, 2005). The gonads and placenta produce a number of hormones. Androgens such as testosterone influence the development and maintenance of the male reproductive tract, secondary sex characteristics, and behavior. In the female, estrogens such as estradiol function in the development and maintenance of the reproductive tract, stimulation of the mammary glands, development of secondary sex characteristics, and the regulation of behavior.
A lot of research has been carried out on the effects of hormones on behavior and it has been determined that even normal fluctuations in hormone levels affects behavior (The Endocri