Short answers, pulled from the story.
Arnold Adolph Berthold proved the existence of the first hormone in 1849 through experiments on roosters. He demonstrated that testes secreted a chemical substance into the bloodstream to control behavior and physical traits without direct physical contact. This discovery laid the groundwork for the field of endocrinology.
Ernest Starling coined the term hormone in 1905. He derived the word from the Greek meaning to arouse or excite to describe chemical messengers that travel along the bloodstream to coordinate body activities. This definition expanded biology to include a complex network of communication beyond the nervous system.
Auxin is the first plant hormone and was isolated in 1933 by Kögl, Haagen-Smit, and Erxleben. Dutch scientist Frits Warmolt Went and Russian scientist Nikolai Cholodny showed in the 1920s that asymmetric accumulation of this growth hormone caused plant bending. Auxin is produced mainly at the tips of young leaves and in the shoot apical meristem.
Lipid-soluble hormones such as steroids pass through the plasma membrane to act within the cell's nucleus. These hormones contain four fused rings derived from cholesterol and bind to intracellular nuclear receptors. The receptors then move into the nucleus to regulate gene expression and activate gene transcription.
The body maintains a delicate balance through a homeostatic negative feedback control mechanism. When blood glucose levels rise, the pancreas secretes insulin to reduce glucose levels and then reduces secretion as levels drop. This cycle depends on factors that influence the metabolism and excretion of hormones.
The most commonly prescribed hormones include estrogens and progestogens for hormonal contraception and hormone replacement therapy. Thyroxine is used for hypothyroidism and steroids treat autoimmune diseases and respiratory disorders. Insulin is used by many diabetics to regulate blood sugar levels.