A hormone is a substance that is produced in tiny amounts in one part of an organism and is transported to other parts where it has a definite physiological effect. Hormones also often affect the functioning of other hormone-producing tissues so that the effects can be complex and integrated. They influence the rate at which reactions proceed. They are important in both animals and plants, affecting growth, differentiation, metabolism, digestive function, mineral and fluid balance.


The rate of secretion, efficacy on target organs, and rate of removal are all affected by numerous factors include feedback from their metabolic effects, mineral or sugar concentration in the blood, and the action of controlling hormones. The latter usually originate in the pituitary gland and those controlling the pituitary in the hypothalamus.


Hormones do not fall into any one particular chemical class. They may be steroids, peptides, or relatively simple compounds such as adrenaline.


In animals, hormones are usually secreted by endocrine glands directly from gland cells into the bloodstream, where they often circulate in combination with serum proteins. They occur copiously in vertebrates but are also known in some invertebrates.


Plant hormones, called phytohormones (e.g., auxins and gibberllins), play a prominent role in plant growth.


Principal hormones in the human body
hormone chemical type secreting gland target
adrenaline modified amino acid adrenal medulla heart
adrenocorticotropic hormone polypeptide anterior pituitary adrenal cortex
androgen steroid testes many tissues
antidiuretic hormone peptide hypothalamus kidneys
atrial natriuretic peptide peptide heart kidneys
calcitonin peptide thyroid peptide
cholecystokinin peptide lining of small intestine pancreas
corticotropin-releasing hormone peptide hypothalamus anterior pituitary
dopamine peptide hypothalamus anterior pituitary
enterogastrone polypeptide lining of small intestine stomach
estrogen steroid ovaries uterus
follicle-stimulating hormone glycoprotein anterior pituitary gonads
gastrin peptide stomach lining stomach
glucagon protein pancreas liver
glucocorticoid steroid adrenal cortex muscles
gonaotrophin-releasing hormone peptide hypothalamus anterior pituitary
growth hormone protein anterior pituitary bones
growth hormone-releasing hormone peptide hypothalamus anterior pituitary
insulin protein pancreas muscles
luteinizing hormone glycoprotein anterior pituitary gonads
melanocyte-stimulating hormone peptide anterior pituitary melanocytes
melatonin modified amino acid pineal gland hypothalamus
mineralocorticoid steroid adrenal cortex kidneys
noradrenaline modified amino acid adrenal medulla heart
oxytocin peptide hypothalamus uterus
parathyroid hormone protein parathyroid bones
progesterone steroid ovaries uterus
prolactin protein anterior pituitary mammary glands
prostaglandin modified fatty acid many tissues many tissues
secretin peptide lining of small intestine pancreas
somatostain peptide pancreas gastrointestinal tract
thymosin peptide thymus white blood cells
thyroid-stimulating hormone glycoprotein anterior pituitary thyroid
thyrotropin-releasing hormone peptide hypothalamus anterior pituitary
thyroxine iodinated amino acid derivative thyroid many tissues
vitamin D sterol skin bones