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Produced by one tissue and conveyed by the bloodstream to another, hormones effect physiological activity, such as growth or metabolism.
Hormones are one of the messengers of the body that are produced by endocrine glands.
Hormone actions vary widely, but can include stimulation or inhibition of growth, phase of life (ex. puberty, pregnancy), induction or suppression of apoptosis (programmed cell death), activation or inhibition of the immune system, and preparation for a new activity (ex . fighting, mating).
Hormones are classified into four groups according to their chemical composition: - Proteins, such as human chorionic gonadotropin and thyroglobulin
- Phenol derivatives, such as epinephrine and norepinephrine,
- Steroids, such as estrogens and androgens
- Peptides, such as insulin and glucagons
As lack of any one of them may cause serious disorders, many of these components are now produced synthetically and used in treatment where there is a deficiency. The most commonly-prescribed are estrogens and progestagens (in the contraceptive pill and as HRT), thyroxine (as levothyroxine, for hypothyroidism) and steroids (for autoimmune diseases and several respiratory disorders). Insulin is used by many diabetics.
A "pharmacologic dose" is a medical usage referring to an amount far greater than naturally occurs in a healthy body. The effects of pharmacologic doses may be different from responses to naturally-occurring amounts and may be therapeutically useful.
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