In at least 500 words: Discuss hormones in the body. You may choose to discuss

In at least 500 words:
Discuss hormones in the body. You may choose to discuss circulating hormones (those produced by the endocrine system), local hormones (ie paracrines), hormones produced by the gut, or recently discovered hormones such as ghrelin, obestatin and leptin. You could discuss their structure, their effects and/or how they exert their effects on their target organs and tissues. You could concentrate on one (or a few) hormones or organs, or you could be more exhaustive in your coverage.