tropic hormone

Some hormones do the work themselves; others are middle managers whose only job is to tell another department to get to work. A tropic hormone is one of those managers — its target is not a muscle or a liver cell but another endocrine gland, which it prods into making and releasing its own hormone.

A tropic hormone is a hormone whose principal target is another endocrine gland, stimulating that gland to grow and to secrete its hormones. Most of the classic tropic hormones come from the anterior pituitary: TSH drives the thyroid, ACTH drives the adrenal cortex, and LH and FSH drive the gonads. Over time, sustained stimulation also enlarges the target gland (a trophic, growth-promoting effect).

Tropic hormones are the middle links in endocrine axes, sitting between a hypothalamic command and a peripheral gland's final output, and they are kept in check by negative feedback from the hormones they elicit. A caveat: the spellings tropic and trophic are often used interchangeably, but they emphasize slightly different ideas — turning a gland on versus making it grow.