The three categories are non-peptide amino acid derivatives and peptide hormones, steroid hormones and monoamines. Peptide hormones are made of chains of amino acids and are secreted into the blood stream and have endocrine functions. One example is prolactin, a peptide hormone that acts on the mammary gland and causes milk to be secreted. Another one is growth hormone that acts on the bones and muscles. These are produced in the anterior pituitary gland. Other organs produce peptide hormones like the heart, the posterior pituitary, the pancreas, the gastrointestinal tract and fat tissue. Non-peptide amino acid derivatives are another type of hormone without peptide connections.Steroid hormones are grouped by the receptors they bind to. Some examples are androgens and estrogens. Steroids control metabolism, inflammation, salt and water balance and sexual development. They are known as lipid and phospholipid hormones. Monoamines are neurotransmitters and neuromodulators and are derived from aromatic amino acids along with thyroid hormones.
Hormones are substances produced by a set of glands in the human body known as endocrine glands. Together, these glands make up the endocrine system. Hormones work as chemical messengers; they are manufactured by various endocrine glands within the body, then dumped into the bloodstream, where they elicit a response from a target tissue somewhere else in the body. The study of hormones and the glands that produce them is known as endocrinology.
There is no one separate category that hormones fit into, but most are protein molecules or steroid molecules. Proteins, of course are made up of various combinations of amino acids. A good example of glands that produce a specific hormone would be the adrenal glands which produce the hormone epinephrine, or adrenaline. Adrenaline is the hormone that produces the "fight or flight" syndrome, which is vital for survival in the wild. A person experiencing a surge of adrenaline is getting ready for the fight of their life, or preparing to run for their life, faster than they ever ran before.