Short answers, pulled from the story.
A hormone is a class of signaling molecules in multicellular organisms that are sent to distant organs or tissues to regulate physiology and behavior. Hormones are defined by their function rather than their structure, and they are required for the normal development of animals, plants, and fungi.
George Oliver and Edward Albert Schäfer discovered the first hormone, adrenaline, in adrenal extracts, publishing their findings in two reports in 1894. The word hormone was later coined by Ernest Starling in 1905, from the Greek meaning to arouse or excite.
In 1849 Arnold Adolph Berthold found that castrated roosters lost their normal sexual and aggressive behaviors, while transplanting a testis into the abdominal cavity restored normal behavior. He concluded that a chemical secreted by the testes, later identified as testosterone, caused these effects regardless of the organ's location.
Hormones include proteins and peptides such as insulin and oxytocin, amino acid derivatives such as melatonin and thyroxine, steroids such as estradiol, testosterone, and cortisol, eicosanoids such as prostaglandin and thromboxane, and gases such as ethylene and nitric oxide. They have diverse chemical structures because hormones are defined functionally, not structurally.
Hormones affect distant cells by binding to specific receptor proteins, which activates a signal transduction pathway that typically increases gene transcription. Water-soluble hormones act on the cell surface via second messengers, while lipid-soluble hormones such as steroids cross the membrane to bind intracellular nuclear receptors.
A hormone acts over a larger spatial and temporal scale and travels through the circulatory system in seconds, minutes, or hours, while a neurotransmitter usually acts across micrometer-scale distances in milliseconds. Neural signaling is all-or-nothing and digital, whereas hormonal signaling is continuously variable based on hormone concentration.
Commonly prescribed hormones include estrogens and progestogens for contraception and hormone replacement therapy, thyroxine as levothyroxine for hypothyroidism, and steroids for autoimmune and respiratory disorders. Insulin is used by many diabetics, and pharmacologic doses of glucocorticoids can suppress inflammation.