Tropic hormones are hormones that have other endocrine glands as their target. Most tropic hormones are produced and secreted by the anterior pituitary.[1] The hypothalamus secretes tropic hormones that target the anterior pituitary, and the thyroid gland secretes thyroxine, which targets the hypothalamus and therefore can be considered a tropic hormone.[2]
The term tropic is from Ancient Greek τροπικός (tropikós), in the sense "of or pertaining to a turn or change", meaning "causing a change, affecting"; this is the same origin as tropic and trope. This should not be confused with trophic, as in similar-sounding trophic hormone – the words and concepts are both unrelated.[3] Tropic hormones are contrasted with non-tropic hormones, which directly stimulate target cells.
Tropic hormones from the anterior pituitary include:
In turn, the hypothalamus controls the release of hormones from the anterior pituitary by secreting a class of hypothalamic neurohormones called releasing and release-inhibiting hormones - which are released to the hypothalamo-hypophyseal portal system and act on the anterior pituitary.[1]